LIGO/Virgo S190426c

The IceCube Collaboration (http://icecube.wisc.edu/) reports:

IceCube has performed a search for track-like muon neutrino events
consistent with the sky localization of S190426c in a time range of 1000
seconds centered on the alert event time (2019-04-26 15:13:35.337 UTC to 2019-04-26 15:30:15.337 UTC)
during which IceCube was collecting good quality data.
No track-like events are found in spatial coincidence with the 90% spatial containment of S190426c calculated from the map
circulated in the preliminary notice. 

IceCube's sensitivity to point sources within the location spanned by the 90% spatial containment of S190426c ranges from
0.029 to 0.644 GeV cm^-2 in a 1000 second time window.

The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica.
The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu

The HAWC Collaboration (https://www.hawc-observatory.org) reports:

The HAWC Collaboration performed a follow-up of the gravitational wave
trigger S190426c. At the time of the trigger, the HAWC
local zenith was oriented towards (RA, Dec) = (347.3 deg, 18.9 deg).
28% of the GW candidate sky location probability fell within our
observable field of view (0-45 deg zenith angle).

We performed a search for a short timescale emission using 6 sliding
time windows (dt = 0.3s, 1s, 3s, 10s, 30s and  100s), shifted forward
in time by 20% of their width. We searched the 95% probability
containment area in a timescale-dependent time period, from t0-5dt to
t0+10dt, where t0 is the time of the GW trigger.

No significant gamma-ray detection above the background was observed.

The sensitivity of this analysis is greatly dependent on zenith angle,
ranging from 33.8 deg to 45.0 deg for the area searched in this
analysis. The 5sigma detection sensitivity to a 1s (100s) burst in the
80-800GeV energy range goes from 1.2e-05 erg/cm^2 to 1.1e-04 erg/cm^2
(5.7e-05 erg/cm^2 to 5.0e-04 erg/cm^2), depending on the zenith
angle.

HAWC is a TeV gamma-ray water Cherenkov array located in the state of
Puebla, Mexico. It is sensitive to the energy range ~0.1-100TeV, and
monitors 2/3 of the sky every day with an instantaneous field-of-view
of ~2 sr.

V. Lipunov, E. Gorbovskoy, V.Kornilov, D.Kuvshinov, N.Tyurina, P.Balanutsa,
A.Kuznetsov, V.V.Chazov, D. Vlasenko
Lomonosov Moscow State University,
Sternberg Astronomical Institute, Moscow State University

A. Tlatov, V.Senik, A.V. Parhomenko, D. Dormidontov
Kislovodsk Solar Station of the Pulkovo Observatory

K. Ivanov, O. Gres, N.M. Budnev, S. Yazev, O. Chuvalaev, V. Poleshchuk
Irkutsk State University

V. Yurkov, A. Gabovich, Yu. Sergienko
Blagoveschensk Educational State University, Blagoveschensk

R. Podesta, Carlos Lopez and F. Podesta
Observatorio Astronomico Felix Aguilar (OAFA)

Hugo Levato and Carlos Saffe
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
The Instituto de Astrofisica de Canarias

D. Buckley, S. Potter, A. Kniazev, M. Kotze
South African Astronomical Observatory



MASTER-Amur robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Russia (Blagoveshchensk State Pedagogical University) started inspect of the LIGO/Virgo S190426c errorbox  3232 sec after trigger time at 2019-04-26 16:15:47 UT, with upper limit up to  18.4 mag. The observations began at zenit distance = 117 deg. The sun  altitude  is -25.7 deg. 

MASTER-Tunka robotic telescope  located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the LIGO/Virgo S190426c errorbox  3803 sec after trigger time at 2019-04-26 16:25:18 UT, with upper limit up to  19.5 mag. The observations began at zenit distance = 125 deg. The sun  altitude  is -24.9 deg. 

The galactic latitude b = -60 deg., longitude l = 98 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/ligo_1.php?id=10199

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

    3323 | 2019-04-26 16:15:47 |         MASTER-Amur | (  2h 50m 29.91s , +85d 53m 31.28s) |   C |   180 | 18.3 |        
    3556 | 2019-04-26 16:19:40 |         MASTER-Amur | ( 14h 14m 37.41s , +85d 56m 38.95s) |   C |   180 | 18.1 |        
    3768 | 2019-04-26 16:23:13 |         MASTER-Amur | (  0h 25m 31.78s , +85d 27m 16.37s) |   C |   180 | 18.4 |        
    3893 | 2019-04-26 16:25:18 |        MASTER-Tunka | ( 22h 27m 30.53s , +83d 55m 49.49s) |   C |   180 | 19.5 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.

The LIGO Scientific Collaboration and the Virgo Collaboration report:

We identified the compact binary merger candidate S190426c during
real-time processing of data from LIGO Hanford Observatory (H1), LIGO
Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-04-26
15:21:55.337 UTC (GPS time: 1240327333.337). The candidate was found
by the GstLAL [1], MBTAOnline [2], PyCBC Live [3], and SPIIR [4]
analysis pipelines.

S190426c is an event of interest because its false alarm rate, as
estimated by the online analysis, is 1.9e-08 Hz, or about one in 1
year, 7 months. The event's properties can be found at this URL:

https://gracedb.ligo.org/superevents/S190426c

The classification of the GW signal, in order of descending
probability, is BNS (49%), MassGap (24%), Terrestrial (14%), NSBH
(13%), or BBH (<1%).

Assuming the candidate is astrophysical in origin, there is strong
evidence for the lighter compact object having a mass < 3 solar
masses (HasNS: >99%). Using the masses and spins inferred from the
signal, there is strong evidence for matter outside the final compact
object (HasRemnant: >99%).

Two skymaps are available at this time and can be retrieved from the
GraceDB event page:
* bayestar.fits.gz, the preliminary sky localization generated by
  BAYESTAR [5], distributed via GCN notice about 25 minutes after
  the candidate,
* bayestar1.fits.gz, an updated localization distributed via GCN
  notice about an hour after the candidate. This is the preferred
  skymap at this time.

For the bayestar1.fits.gz skymap, the 90% credible region is 1262
deg2. Marginalized over the whole sky, the a posteriori luminosity
distance estimate is 375 +/- 108 Mpc (a posteriori mean +/- standard
deviation).

For further information about analysis methodology and the contents of
this alert, refer to the LIGO/Virgo Public Alerts User Guide
<https://emfollow.docs.ligo.org/userguide/><https://emfollow.docs.ligo.org/userguide/>.

[1] Messick et al. PRD 95, 042001 (2017)
[2] Adams et al. CQG 33, 175012 (2016)
[3] Nitz et al. PRD 98, 024050 (2018)
[4] Qi Chu, PhD Thesis, The University of Western Australia (2017)
[5] Singer & Price PRD 93, 024013 (2016)

[GCN OPS NOTE(30apr19): Per author's request, the double spacing was removed.]

Antonio Martin-Carrillo (UCD, Dublin)
V. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland)
J. Rodi (IAPS-Roma, Italy)
A. Coleiro (APC, France)
S. Mereghetti (INAF IASF-Milano, Italy)

on behalf of the INTEGRAL multi-messenger collaboration:
https://www.astro.unige.ch/cdci/integral-multimessenger-collaboration

Using combination of INTEGRAL all-sky detectors (following Savchenko
et al. 2017, A&A 603, A46): SPI/ACS, IBIS/Veto, and IBIS we have
performed a search for a prompt gamma-ray counterpart of S190426c (GCN
24237
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 ).

At the time of the event (2019-04-26 15:21:55 UTC, hereafter T0),
INTEGRAL was operating in nominal mode. The peak of the event
localization probability was at an angle of 59 deg with respect to the
spacecraft pointing axis. This orientation implies strongly suppressed
(14% of optimal) response of ISGRI, strongly suppressed (29% of
optimal) response of IBIS/Veto, and somewhat suppressed (60% of
optimal) response of SPI-ACS.

The background within +/-300 seconds around the event was very stable
(excess variance 1.2).

We have performed a search for any impulsive events in INTEGRAL SPI-
ACS (as described in Savchenko et al. 2012, A&A 541A, 122S), IBIS, and
IBIS/Veto data.

We do not detect any significant counterparts and estimate a 3-sigma
upper limit on the 75-2000 keV fluence of 1.7e-07 erg/cm^2 for a burst
lasting less than 1 s with a characteristic short GRB spectrum (an
exponentially cut off power law with alpha=-0.5 and Ep=600 keV)
occurring at any time in the interval within 300 s around T0. For a
typical long GRB spectrum (Band function with alpha=-1, beta=-2.5, and
Ep=300 keV), the derived peak flux upper limit is ~1.4e-07 (4.9e-08)
erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.

Gergely D��lya and Peter Raffai (Eotvos Univ.) reports on behalf of the GLADE
team:

We have found 13,960 galaxies in the GLADE catalog [1,2], within the
updated 90% GW
localization area (bayestar1.fits.gz, the preferred skymap) reported by the
LVC in GCN 24237
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 , and within 423 +/- 128 Mpc distance limits.

The galaxies found can be accessed on the GLADE website (4 MB txt file;
please note that the order of galaxies in the list only follow the ordering
as the appear in GLADE):
http://glade.elte.hu/O3/S190426c_GLADE_90_1sigma.txt

There are 935 galaxies within the 50% GW localization area and within
the same distance limits (253 kB txt file; please note that the order of
galaxies in the list only follow the ordering as the appear in GLADE):
http://glade.elte.hu/O3/S190426c_GLADE_50_1sigma.txt

[1] D��lya, G., Galg��czi G., Dobos, L. et al., 2018 MNRAS, 479, 2374
[2] http://glade.elte.hu

G. Piano, M. Cardillo (INAF/IAPS), M. Tavani (INAF/IAPS, and Univ. Roma Tor
Vergata), F. Verrecchia (SSDC, and INAF/OAR), A. Ursi, C. Casentini
(INAF/IAPS), F. Lucarelli, C. Pittori (SSDC, and INAF/OAR), A. Bulgarelli,
N. Parmiggiani (INAF/OAS-Bologna), M. Pilia (INAF/OA-Cagliari), F. Longo
(Univ. Trieste, and INFN Trieste),

report on behalf of the AGILE Team:

In response to the LIGO-Virgo GW event S190426c at T0 = 2019-04-26
15:21:55.337 (UT), we performed a preliminary analysis of the AGILE
Gamma-Ray Imaging Detector (GRID) at different timescales in the energy
range 50 MeV - 10 GeV.

At T0 the accessible LIGO/Virgo 90% c.l. localization region (LR), which
includes the Celestial North Pole, was observed at off-axis angles between
10 and 70 deg. Preliminary values of 3-sigma upper limits (UL) obtained at
LIGO/Virgo trigger time (T0) are:

(1) from 5.5e-7 to 3.2e-6 erg cm^-2 s^-1 for an integration time of 5s
starting from T0, with the GRID exposure covered nearly 75% of this part of
the LR.

(2) from 2.8e-7 to 1.6e-6  erg cm^-2 s^-1 for an integration time of 10s
starting from T0, with the GRID exposure covered nearly 80% of this part of
the LR.

(3) from 3.9e-8 to 1.6e-7  erg cm^-2 s^-1 for an integration time of 100s
starting from T0, with the GRID exposure covered 100% of this part of the
LR.

The other part of the LR (R.A. in the approximate range between 10 - 16 hr)
was partly occulted by the Earth at T0, and is currently in the region not
accessible by the GRID because of solar panel constraints.

These measurements were obtained with AGILE observing a large portion of
the sky in spinning mode. Additional analysis of AGILE data is in progress.

Gu Lim (SNU), Myungshin Im (SNU), Gregory S.H. Paek (SNU), Joonho Kim
(SNU), Sungyong Hwang (SNU), Bomi Park (SNU), Sophia Kim (SNU), Changsu
Choi (SNU),  Hyung Mok Lee (KASI), on behalf of a larger collaboration

We observed host galaxy candidates in the 90% localization area of S190426c
using SNU Astronomical Observatory (SAO) 1m telescope, starting at
2019-04-26 16:27:00 UT. We covered 19 candidate hosts as listed below. No
apparently bright transient has been spotted in these galaxies.

NAME                                             RA            DEC
2MASS+20242545+4854496  20:24:25.452 48:54:49.662
2MASS+20382080+5932155  20:38:20.808 59:32:15.504
2MASS+20435949+5314323  20:43:59.495 53:14:32.302
2MASS+20282997+5119418  20:28:29.978 51:19:41.855
2MASS+20250165+5251250  20:25:1.655 52:51:25.099
2MASS+01300015+8211097  01:30:0.151 82:11:9.780
2MASS+20252061+6132513  20:25:20.618 61:32:51.385
2MASS+01111091+8130123  01:11:10.914 81:30:12.305
2MASS+20461177+5629408  20:46:11.770 56:29:40.830
2MASS+20210572+4858452  20:21:5.728 48:58:45.224
2MASS+20255146+5356137  20:25:51.467 53:56:13.765
2MASS+20225227+4905194  20:22:52.273 49:05:19.468
PGC2352175                              20:18:7.244 49:44:43.465
2MASS+20201548+4720364  20:20:15.483 47:20:36.402
2MASS+20203838+4734038  20:20:38.386 47:34:3.882
2MASS+20532613+6326079  20:53:26.133 63:26:7.915
2MASS+20343526+5423228  20:34:35.266 54:23:22.859
2MASS+20260256+5552523  20:26:2.563 55:52:52.399
2MASS+20254165+5323347  20:25:41.653 53:23:34.778

���

C. Fletcher (USRA) reports on behalf of the Fermi-GBM Team and the
GBM-LIGO/Virgo group:

For S190426c, and using the updated BAYESTAR skymap, Fermi-GBM was
observing 100% of the localization probability at event time.

There was no Fermi-GBM onboard trigger around the event time of the
LIGO/Virgo detection of GW trigger S190426c (GCN 24237
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 ). An automated,
blind search for short gamma-ray bursts below the onboard triggering
threshold in Fermi-GBM also identified no counterpart candidates. The GBM
targeted search, the most sensitive, coherent search for GRB-like signals,
was run from +/-30 s around merger time, and also identified no counterpart
candidates.

We therefore set upper limits on impulsive gamma-ray emission.  Using the
representative soft, normal, and hard GRB-like spectral templates described
in arXiv:1612.02395
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 , we set the following 3 sigma flux upper limits over
10-1000 keV (in units of 10^-7 erg/s/cm^2):

Timescale  Soft     Normal   Hard
------------------------------------
0.1 s:     3.9-7.0  8.3-12.  26.-30.
1.0 s:     1.2-2.2  2.6-3.7  7.7-8.8
10  s:     0.4-0.7  0.8-1.1  2.4-2.7

Assuming the mean luminosity distance of ~375 Mpc from the GW detection, we
estimate intrinsic luminosity upper limits of (0.09-1.6)E49 erg/s for the
soft template, (0.2-2.6)E49 erg/s
for the normal template, and (0.9-10.6)E49 erg/s for the hard template over
the 1 keV-10 MeV energy range.

Iair Arcavi (Tel Aviv University), Curtis McCully (LCO), Daichi Hiramatsu
(LCO/UCSB), D. Andrew Howell (LCO/UCSB), Jamison Burke (LCO/UCSB), Craig
Pellegrino (LCO/UCSB) on behalf of the Las Cumbres GW Follow-up
Collaboration

We detect a possible transient at RA Dec 217.28296 -38.190458,

which we tentatively name ���Nemo���, on the outskirts of the galaxy 2MASX
J14290828-3811214 (redshift 0.07478 / distance 338 Mpc; Jones et al. 2009,
���The 6dF Galaxy Survey Data Release 3,��� via NED).


We measure a preliminary aperture magnitude of 19.74 +- 0.12 in the i-band
(but host contamination is likely) in a 300s image taken on 2019-04-26
18:19:33 UT at a Las Cumbres SAAO 1m telescope. This corresponds to an
absolute magnitude of -17.9 at this distance. These values are corrected
for MW extinction (E(B-V) = 0.0874; Schlafly, E.F. & Finkbeiner, D.P.
 2011, ApJ 737, 103).

���Nemo��� is not visible in g-band images taken at the same time (2019-04-26
18:13:52 UT) using a Las Cumbres SAAO 1m. The source does not appear in DSS
red or blue images, though they are not as deep as our discovery image. The
transient is also not visible in images taken from the Las Cumbres
Observatory 2m Faulkes telescope in the i band at 16:27:54, the r band at
16:33:39 , and the g band at 16:39:24 (all on 2019-04-26; all times UT) but
these images are also shallower than the discovery image. Therefore the
transient nature of ���Nemo��� is not yet confirmed.

G. P. Smith (Birmingham), M. Bianconi (Birmingham), R. Massey (Durham), 
and A. Robertson (Durham) report on behalf of the Gravitationally Lensed 
Gravitational Wave Hunters

The non-zero value of Prob_MassGap identifies S190426c (GCN24237
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 ) as a 
possible strongly-lensed NS-NS merger - i.e. its true redshift and 
luminosity distance may be larger, and true mass may be smaller than 
inferred by LIGO/Virgo.  The rate of such detections is predicted to be 
~0.01 per Earth year during O3.

The putative lens could be an individual galaxy, or a group/cluster of 
galaxies.  None of the 130 known strong-lensing clusters in the sample 
discussed by Smith et al. (2018) are located in the updated 90% credible 
sky localization released an hour after detection and stated as the 
currently preferred skymap in GCN24237
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 .

At the estimated luminosity distance to the source (D_L~375Mpc; 
GCN24237
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 ) an AT2017gfo
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 -like counterpart would have an apparent B/V-band 
magnitude of AB<~24.5 within ~2 days of the LIGO/Virgo detection.  This 
estimate (albeit redshifted in to the i-band, and time-dilated to ~4 
days post-detection) is also valid if the source is strongly-lensed and 
actually at a redshift of z~1.

We encourage colleagues to observe the sky localization of this source 
down to AB~25, to search for a kilonova-like counterpart, and thus 
explore the possibility that this source is strongly-lensed, for example 
by a massive galaxy or group of galaxies.

Background information on the details of this circular can be found in 
these publications:

Smith, Jauzac, Veitch, et al., 2018, MNRAS, 475, 3823
Smith, Robertson, Bianconi, Jauzac, arXiv:1902.05140
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Smith, Bianconi, Jauzac, et al., 2019, MNRAS, 485, 5180

Iair Arcavi (Tel Aviv University), Curtis McCully (LCO), Daichi Hiramatsu
(LCO/UCSB), D. Andrew Howell (LCO/UCSB), Jamison Burke (LCO/UCSB), Craig
Pellegrino (LCO/UCSB) on behalf of the Las Cumbres GW Follow-up
Collaboration


The potential transient we reported in Arcavi et al. (Nemo; GCN 24249
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 ) is
visible in i-band DECam images taken on 2017-05-03 03:08:06 UT (retrieved
through the NOAO Data Lab). It is therefore unrelated to the LIGO/Virgo
S190426c event.

C. D. Bochenek (Caltech), S. R. Kulkarni (Caltech), D. McKenna (Caltech), K. Belov (JPL), V. Ravi (Harvard, Caltech), T. Callister (Caltech)

STARE2 is an all-sky instrument located at the Owens Valley Radio Observatory (OVRO) and the Goldstone Deep Space Communications Complex designed to search for fast radio transients. STARE2 is sensitive to millisecond duration bursts of radio emission above 157 kJy, for a burst at zenith. STARE2 regularly sees type IIIdm bursts from the Sun.

No candidate events were found within 3 hours of the LIGO/Virgo S190426c.

Observing frequency: 1280-1530 MHz
Time resolution: 65.536 microseconds
Maximum timescale STARE2 is sensitive to: 34 ms
Frequency resolution: 122.07 kHz
Dispersion measure search range: 5 pc cm^-3 - 3000 pc cm^-3

A map of our upper limit as a function of RA and DEC can be found at: http://www.astro.caltech.edu/~cbochenek/LIGO_VIRGO_S190426c_limits.png


The sky at OVRO at the time of the event contains 76% of the LIGO localization region.

S. D. Barthelmy (NASA/GSFC), A. Y. Lien (GSFC/UMBC),
D. M. Palmer (LANL), T. Sakamoto (AGU),
A. A. Breeveld (MSSL-UCL), A. P. Beardmore (U. Leicester),
D. N. Burrows (PSU), S. Campana (INAF-OAB), S. B. Cenko (NASA/GSFC),
G. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA),
P. D'Avanzo (INAF-OAB), V. D'Elia(ASDC), S. Emery (UCL-MSSL),
P. A. Evans (U. Leicester), P. Giommi (ASI), C. Gronwall (PSU),
D. Hartmann (Clemson U.), J. A. Kennea (PSU), H. A. Krimm (NSF),
N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC),
A. Melandri (INAF-OAB), B. Mingo (U. Leicester), J. A. Nousek (PSU),
S. R. Oates (Uni. of Warwick), P. T. O'Brien (U. Leicester),
J. P. Osborne (U. Leicester), C. Pagani (U. Leicester),
K. L. Page (U.Leicester), M. Perri (ASDC),
J. L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU),
M. H. Siegel (PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu (PSU),
E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift team:

We report the search results in the BAT data within T0 +/- 100 s of the
LVC event S190426c (LIGO/VIRGO Collaboration GCN Circ. 24237
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 ),
where T0 is the LVC trigger time (2019-04-26T15:21:55.337 UTC).

The center of the BAT field of view (FOV) at T0 is
RA = 255.327 deg,
DEC = -7.000 deg,
ROLL = 77.470 deg.
The BAT FOV (>10% partial coding) covers 5.22% of the integrated
LVC localization probability, and 6.39% of the galaxy convolved
probability (Evans et al. 2016).

Within T0 +/- 100 s, no significant detections (signal-to-noise ratio
>~ 5 sigma) are found in the BAT raw light curves with time bins of
64 ms, 1 s, and 1.6 s. Assuming an on-axis (100% coded) short GRB with a
typical spectrum in the BAT energy range (i.e., a simple power-law model
with a power-law index of -1.32, Lien & Sakamoto et al. 2016), the 5-sigma
upper limit in the 1-s binned light curve corresponds to a flux upper
limit (15-350 keV) of ~ 8.10 x 10^-8 erg/s/cm^2.

No event data are available at this point.

BAT retains decreased, but significant, sensitivity to rate increases for
gamma-ray events outside of its FOV. About 94.56% of the integrated LVC
localization probability was outside of the BAT FOV but above the
Earth's limb from Swift's location, and the corresponding flux upper limits
for this region are within roughly an order of magnitude higher than those
within the FOV.

The results of the BAT analysis are available at
https://swift.gsfc.nasa.gov/results/BATbursts/team_web/S190426c/web/source.html

Daniel A. Goldstein (Caltech), Igor Andreoni (Caltech), Michael
Coughlin (Caltech), Mansi M. Kasliwal (Caltech), Peter E. Nugent
(LBNL), Joshua S. Bloom (UC Berkeley), Keming Zhang (UC Berkeley),
Shreya Anand (Caltech), Jennifer Barnes (Columbia), S. Bradley Cenko
(NASA GSFC), Jeffrey Cooke (Swinburne), Jorge Mart��nez Palomera (UC
Berkeley), Leo P. Singer (NASA GSFC), on behalf of the Global Relay of
Observatories Watching Transients Happen (GROWTH) and ZTF
collaborations:

We are observing the ecliptic lobe and southern regions of the
northern lobe of the localization region of the gravitational wave
trigger S190426c (LIGO Scientific Collaboration and the Virgo
Collaboration, GCN #24237
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 ) with the Victor M. Blanco 4m Telescope at
Cerro Tololo Inter-American Observatory, equipped with the Dark Energy
Camera (DECam). An observational tiling for the event was
automatically and optimally determined and triggered using the GROWTH
Target of Opportunity marshal (Coughlin et al. 2019a, Kasliwal et al.
2019b). We plan to observe 35% of the integrated probability and more
than 800 square degrees with 30 second visits in r and 50 in z. Our
limiting magnitudes are expected to be ~22.9 in r and ~22.4 in z,
based on the DECam exposure time calculator
(http://www.ctio.noao.edu/noao/sites/default/files/DECam/DECam_ETC-ARW-RCS7.xls).

The data from this program are immediately public and we invite anyone
interested to search the images for optical counterparts. We are
searching the images in real time for optical counterpart candidates
using an image subtraction pipeline written for this program. We
invite anyone interested to download the images. The images are
available under proposal ID 2019A-0205 from the NOAO archive
(archive.noao.edu). For any questions on the data or the observations,
please contact the PIs of this program, Danny Goldstein and Igor
Andreoni (danny@caltech.edu, andreoni@caltech.edu).

GROWTH and ZTF are worldwide collaborations comprising Caltech, USA;
IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA;
DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; TTU, USA; LANL USA;
Tokyo Tech, Japan; IIT-B, India; IIA, India; LJMU, UK and USyd,
Australia. ZTF acknowledges the generous support of the NSF under AST
MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF
under PIRE Grant No 1545949. Alert distribution service provided by
DIRAC@UW (Patterson et al. 2019). Alert filtering and follow-up
co-ordination is being undertaken by the GROWTH marshal system
(Kasliwal et al. 2019).

V. Bhalerao, H. Kumar, V. Karambelkar, K. Deshmukh, D. Saraogi (IITB), G. C. Anupama, T. Stanzin, J. Stanzin (IIA) report on behalf of the GROWTH collaboration:

We followed up the localisation region of the GW candidate event S190426c with the GROWTH-India telescope. We obtained 31 r-band overlapping images covering a total area of 7.5 square degrees, with 3.9% probability of containing the GW counterpart. Exposures were 600 seconds long, and reached a typical depth of 20.5 magnitude. The field centres (given below) were chosen in coordination with ZTF and DECAM (GCN 24257
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 ) to cover the northernmost part of the sky not accessible to them. These fields contain 56 galaxies from the GLADE catalog and 5 galaxies from NED. Names and coordinates of the galaxies are also given below.

We do not find any new candidate counterparts in these fields.

List of observed fields:
ra dec
339.545 85.979
342.692 85.247
346.500 86.345
337.500 84.882
337.500 86.345
331.364 85.979
348.750 85.613
352.059 83.784
356.250 85.613
356.786 84.882
345.000 84.516
356.538 85.247
358.336 86.028
357.188 84.150
333.750 85.613
313.533 84.081
335.769 85.247
003.214 84.882
003.000 84.516
349.615 85.247
002.812 84.150
355.909 85.979
351.562 84.150
341.250 85.613
351.000 84.516
347.727 85.979
345.938 84.150
350.357 84.882
357.000 84.516
357.353 83.784
343.929 84.882

List of galaxies from NED:
351.959 85.591 VII Zw 941
352.416 85.861 2MASX J23293953+8551387
358.336 86.028 MCG +14-01-004
313.533 84.081 UGC 11664 NED01
349.941 85.373 kkh 095

List of galaxies from GLADE:
ra dec name
356.005 83.640 2MASSJ23440128+8338231
355.713 83.626 2MASSJ23425102+8337319
358.775 83.909 2MASSJ23550596+8354321
359.847 83.786 2MASSJ23592318+8347099
000.843 83.890 2MASSJ00032224+8353232
350.471 83.798 2MASSJ23215295+8347536
333.012 85.867 2MASSJ22120284+8552027
335.994 86.574 2MASSJ22235866+8634273
337.236 84.779 2MASSJ22285658+8446453
336.437 85.302 2MASSJ22254483+8518062
339.315 84.712 2MASSJ22371570+8442429
339.330 86.568 2MASSJ22371927+8634059
341.079 84.767 2MASSJ22441891+8445595
343.365 85.671 2MASSJ22532770+8540144
343.507 84.754 2MASSJ22540162+8445139
343.191 86.590 2MASSJ22524594+8635254
344.556 83.900 2MASSJ22581350+8354006
345.426 84.612 2MASSJ23014222+8436430
347.221 84.347 2MASSJ23085305+8420475
347.491 84.232 2MASSJ23095774+8413568
347.547 84.580 2MASSJ23101130+8434478
347.305 85.200 2MASSJ23091312+8512017
346.687 86.588 2MASSJ23064494+8635164
348.821 84.565 2MASSJ23151704+8433526
348.365 85.910 2MASSJ23132761+8554374
348.279 85.913 2MASSJ23130697+8554472
349.952 85.246 2MASSJ23194838+8514443
349.426 85.675 2MASSJ23174216+8540308
351.498 84.983 2MASSJ23255954+8458585
352.401 85.455 2MASSJ23293632+8527167
352.092 85.487 2MASSJ23282212+8529128
353.146 84.606 2MASSJ23323509+8436200
353.222 85.505 2MASSJ23325329+8530171
353.717 85.459 2MASSJ23345217+8527335
354.043 86.052 2MASSJ23361042+8603066
356.314 84.982 2MASSJ23451539+8458560
356.520 85.413 2MASSJ23460476+8524454
356.634 86.255 2MASSJ23463222+8615196
357.738 85.186 2MASSJ23505702+8511090
357.681 85.643 2MASSJ23504338+8538359
358.058 86.274 2MASSJ23521403+8616272
358.615 84.161 2MASSJ23542759+8409392
358.618 84.422 2MASSJ23542829+8425182
358.486 84.423 2MASSJ23535669+8425237
359.447 85.001 2MASSJ23574733+8500029
000.425 84.862 2MASSJ00014210+8451427
000.209 85.273 2MASSJ00005020+8516227
001.538 84.444 2MASSJ00060903+8426372
001.427 85.020 2MASSJ00054249+8501112
002.342 85.111 2MASSJ00092210+8506409
002.206 85.919 2MASSJ00084951+8555097
002.022 85.871 2MASSJ00080534+8552153
003.587 84.672 2MASSJ00142097+8440183
004.330 84.212 2MASSJ00171922+8412432
345.896 83.870 2MASSJ23033508+8352127
353.130 83.854 2MASSJ23323111+8351147

S. Sugita, M. Serino (AGU), M. Sugizaki, N. Kawai (Tokyo Tech),  H.
Negoro (Nihon U.),
M. Nakajima, W. Maruyama, M. Aoki, K. Kobayashi (Nihon U.),
S. Nakahira, T. Mihara, T. Tamagawa, M. Matsuoka (RIKEN),
T. Sakamoto, H. Nishida, A. Yoshida (AGU),
Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.),
M. Shidatsu (Ehime U.),
M. Oeda, K. Shiraishi (Tokyo Tech),
S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai,
M. Tominaga (JAXA),
Y. Ueda, A. Tanimoto, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake
(Kyoto U.),
H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.),
M. Yamauchi, S. Iwahori, Y. Kurihara (Miyazaki U.),
T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU)
report on behalf of the MAXI team:

We examined the MAXI/GSC all-sky X-ray images (2-20 keV) obtained
in the orbit after the LVC trigger
S190426c at 2019-04-26 15:21:55.337 UTC (GCN 24237
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 ).

At the trigger time of S190426c, the high-voltage of MAXI/GSC was off,
and it was turned on at T0+750 sec (=T0+12.5 min).
The one-orbit (92 min) scan of GSC covered 84% of the 90% credible region
of the bayestar1 skymap from 15:34:25 to 16:36:43���UTC (T0+750 to T0+4488 sec).

No significant new source was found in the region at the one-orbit scan.
The 1-sigma averaged upper limit obtained
from the scan was 18 mCrab at 4-10 keV.

If you require information of X-ray flux by MAXI/GSC at specific coordinates,
please contact the submitter of this circular by email.

Igor Andreoni (Caltech), Daniel A. Goldstein (Caltech), Michael Coughlin (Caltech), Mansi M. Kasliwal (Caltech), Peter E. Nugent (LBNL), Keming Zhang (UC Berkeley), Jorge Mart��nez Palomera (UC Berkeley), Shreya Anand (Caltech), Joshua S. Bloom (UC Berkeley), S. Bradley Cenko (NASA GSFC), Jeffrey Cooke (Swinburne/OzGrav), Leo P. Singer (NASA GSFC), on behalf of the Global Relay of Observatories Watching Transients Happen (GROWTH) and ZTF collaborations:


We report transients identified during the imaging of the localization region of the gravitational wave trigger S190426c (LIGO Scientific Collaboration and the Virgo Collaboration, GCN #24237
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 ) with the Victor M. Blanco 4m Telescope at Cerro Tololo Inter-American Observatory, equipped with the Dark Energy Camera (DECam).

The observational tiling for the event was automatically and optimally determined and triggered using the GROWTH Target of Opportunity marshal (Coughlin et al. 2019a, Kasliwal et al. 2019b). Observations were performed under NOAO proposal ID 2019A-0205 (PIs Andreoni & Goldstein) and are publicly accessible (Goldstein et al., GCN 24257
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 ).

Data are being processed in real time with an image-subtraction pipeline developed specifically for this program. References are taken from the Dark Energy Survey DR1 (https://www.darkenergysurvey.org/the-des-project/data-access/) and DECaLS DR6 & DR7 (http://legacysurvey.org/). The pipeline uses ���autoscan��� (Goldstein et al. 2015) to aid the rejection of spurious sources. 

The following criteria were adopted to select the candidates reported here. The candidates were detected at least twice and were automatically identified in images taken in both r and z filters.  Photometric data points were separated at least by 30 minutes to reject moving objects.  

In a first table we report red sources, with  r-z > 0.5 magnitude.  The photometry measurements are preliminary.

     name |   ra  | dec  | filter | magpsf  | sigmamagpsf | filter | magpsf | sigmamagpsf
 DG19ftnb | 167.595543634942 | -4.35881059496403 | z | 20.39 | 0.08 | r | 20.65| 0.05
 DG19kqxe | 163.781652700717 | -0.23762887433652 | z | 21.05 | 0.11 | r | 22.07| 0.12
 DG19nmaf | 163.752330220064 | -1.4870117224704 | z | 21.60 | 0.10 | r | 22.89| 0.20
 DG19ouub | 171.473293011207 | -9.488486251543 | z | 21.61 | 0.11 | r | 22.12| 0.10
 DG19vkgf | 165.844308606225 | -7.91746108580108 | r | 19.88 | 0.01 | z | 19.57| 0.03
 DG19zdwb | 167.296767466399 | -2.26827548599056 | z | 22.00 | 0.09 | r | 22.80| 0.11
 DG19zyaf | 163.471809253725 | -1.15111319177025 | z | 21.55 | 0.09 | r | 22.66| 0.12

In a second table we report blue sources, with r-z < -0.4 magnitude.
     name |   ra  | dec  | filter | magpsf  | sigmamagpsf | filter | magpsf | sigmamagpsf
 DG19pklb | 168.658599720568 |  -6.9754468556027 | z | 21.27 | 0.14 | r | 20.66 | 0.08
 DG19ytre | 167.760353542608 | 0.527178183535021 | r | 20.69 | 0.03 | z | 21.29 | 0.07

The sources are not coincident with minor planets present in the Minor Planet Center or transients already reported in the Transient Name Server. 

The contact people for this circular are Igor Andreoni (andreoni@caltech.edu) and Danny Goldstein (danny@caltech.edu)

GROWTH and ZTF are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; TTU, USA; LANL USA; Tokyo Tech, Japan; IIT-B, India; IIA, India; LJMU, UK and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert filtering and follow-up coordination is being undertaken by the GROWTH marshal system (Kasliwal et al. 2019).

This research draws upon DECam data as distributed by the Science Data Archive at NOAO. NOAO is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation.
This project used data obtained with the Dark Energy Camera (DECam), which was constructed by the Dark Energy Survey (DES) collaboration.

P.A. Evans (U. Leicester), J.A. Kennea (PSU), A. Tohuvavohu (PSU), S.D.
Barthelmy (NASA/GSFC), A.P. Beardmore (U. Leicester), A.A. Breeveld
(UCL-MSSL), D.N. Burrows (PSU), S. Campana (INAF-OAB), S.B. Cenko
(NASA/GSFC), G. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P.
D'Avanzo (INAF-OAB), V.D'Elia(ASDC), S.W.K. Emery (UCL-MSSL), P. Giommi
(ASI), C. Gronwall (PSU), H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin
(UCL-MSSL), A.Y. Lien (GSFC/UMBC), F.E. Marshall (NASA/GSFC), A.
Melandri (INAF-OAB), J.A. Nousek (PSU), S.R. Oates (U. Warwick), P.T.
O'Brien (U. Leicester), J.P. Osborne (U. Leicester), C. Pagani (U.
Leicester), K.L. Page (U.Leicester), D.M. Palmer (LANL), M. Perri
(ASDC), J.L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU), M.H.
Siegel (PSU), G. Tagliaferri (INAF-OAB), E. Troja (NASA/GSFC/UMCP)
report on behalf of the Swift team:

Swift has performed a series of 197 observations, covering 197 separate
locations within the LVC error region for the GW trigger S190426c
convolved with the 2MPZ catalogue (Bilicki et al. 2014, ApJS, 210, 9),
using the 'bayestar1' GW localisation map. As this is a 3D skymap,
galaxy distances were taken into account in selecting which ones to
observe. The observations currently span from 8.6 ks to 43 ks after the
LVC trigger, and cover 21.5 sq degrees on the sky (corrected for
overlaps). 


We have detected 3 X-ray sources, described below. Other sources that
have been distributed as counterpart notices have been identified as
artifacts or diffuse emission and are not described below.

Source 5 is potentially interesting, as its flux is higher (at
2.1-sigma singificance) than in previous XRT observations (see
http://www.swift.ac.uk/1SXPS/1SXPS%20J144850.8-400845 for the
historical dataset in the 1SXPS catalogue). However, it is only 2.2"
away from a know Seyfert 1 at z=0.123 (from SIMBAD), and therefore it
is more likely that this is simply an unrelated flare from that source.
Observations are, nonetheless encouraged.


Each source is assigned a rank of 1-4 which describes how likely it is
to be related to the GW trigger, with 1 being the most likely and 4
being the least likely. The ranks are described at
http://www.swift.ac.uk/ranks.php.

We have found:

  * 0 sources of rank 1
  * 0 sources of rank 2
  * 0 sources of rank 3
  * 3 sources of rank 4

For all flux conversions and comparisons with catalogues and upper
limits from other missions, we assumed a power-law spectrum with
NH=3e20 cm^2, and photon index (Gamma)=1.7


RANK 4 sources
==============

These are catalogued X-ray sources, showing no signs of outburst
compared to previous observations, so they are not likely to be related
to the GW trigger.
  
  Source 3:
  =============
    RA: 	 346.9414 ( = 23h 07m 45.94s) J2000
    Dec:	 +83.1619 ( = +83d 09' 42.8") J2000
    Error:	 +24.9 (arcsec, radius, 90% confidence).
    Peak Rate:	 7.1e-02 +/- 3.7e-02 ct/sec (0.3-10 keV)
    Peak Flux:	 3.1e-12 +/- 1.6e-12 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  1RXS J230740.9+830945 in the ROSAT/RASSFSC catalogue
    Separation:  9.4" from the XRT source
    Cat Rate:	 3.4e-02 +/- 8.3e-03 ct/sec 
    Cat Flux:	 9.5e-13 +/- 2.3e-13 erg cm^-2 s^-1 (0.3-10 keV)
       so the source  is 1.3-sigma above the catalogued flux.
    There is no evidence for fading.
    NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy
      which is consistent (within 3-sigma) with the distance to the GW
object.
    A SIMBAD object `1RXS J230740.9+830945' is 9.4" away.
    There are 2 2MASS objects within the source's 3-sigma error radius.

  
  Source 5:
  =============
    RA: 	 222.2116 ( = 14h 48m 50.78s) J2000
    Dec:	 -40.1461 ( = -40d 08' 46.0") J2000
    Error:	 +11.5 (arcsec, radius, 90% confidence).
    Peak Rate:	 1.6e-01 +/- 6.3e-02 ct/sec (0.3-10 keV)
    Peak Flux:	 7.0e-12 +/- 2.7e-12 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  1SXPS J144850.8-400845 in the 1SXPS catalogue
    Separation:  0.8" from the XRT source
    Cat Rate:	 3.0e-02 +/- 2.1e-03 ct/sec 
    Cat Flux:	 1.3e-12 +/- 9.0e-14 erg cm^-2 s^-1 (0.3-10 keV)
       so the source  is 2.1-sigma above the catalogued flux.
    There is no evidence for fading.
    NOTE: this source is NOT within 200 kpc of a GWGC or 2MPZ galaxy
      which is consistent (within 3-sigma) with the distance to the GW
object.
    A SIMBAD object `2MASS J14485097-4008456' is 2.2" away.
    There are 3 2MASS objects within the source's 3-sigma error radius.

  
  Source 6:
  =============
    RA: 	 220.9883 ( = 14h 43m 57.19s) J2000
    Dec:	 -39.1433 ( = -39d 08' 35.9") J2000
    Error:	 +5.3 (arcsec, radius, 90% confidence).
    Peak Rate:	 2.1e-01 +/- 5.8e-02 ct/sec (0.3-10 keV)
    Peak Flux:	 8.9e-12 +/- 2.5e-12 erg cm^-2 s^-1 (0.3-10 keV)
    Cat Source:  1SXPS J144357.1-390839 in the 1SXPS catalogue
    Separation:  3.4" from the XRT source
    Cat Rate:	 4.3e-01 +/- 5.5e-03 ct/sec 
    Cat Flux:	 1.9e-11 +/- 2.4e-13 erg cm^-2 s^-1 (0.3-10 keV)
       so the source is not above the catalogued flux.
    There is no evidence for fading.
    There is 1 GWGC or 2MPZ galaxy within 200 kpc of the source.

      and consistent (within 3-sigma) with the distance to the GW
object.
    A SIMBAD object `NAME WISEA J144357.20-390840.0' is 4.3" away.
    There is 1 2MASS object within the source's 3-sigma error radius.

This circular is an official product of the Swift team.

K. De (Caltech), L. Yan (Caltech), C. Fremling (Caltech), I. Andreoni
(Caltech), D. Goldstein (Caltech) report on behalf of the ZTF and
GROWTH collaborations

We report on Target of Opportunity follow-up imaging and spectroscopy
of the red transient DG19vkgf found in DECam imaging (Goldstein et
al., GCN #24257
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 ; Andreoni et al., GCN #24268
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 ) of the localization
region of S190426c (LIGO Scientific Collaboration and the Virgo
Collaboration, GCN #24237
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 ). Spectra were obtained using the Double
Beam Spectrograph (DBSP; Oke & Gunn 1982) on the Hale 200-inch
telescope (P200) at Palomar observatory. We also obtained follow-up
imaging of the source with the Wafer Scale Imager for Prime (WASP) on
P200.

Due to the high airmass of the observation and poor seeing, the
transient is not clearly identified in the trace, but we confirm a
host redshift of z = 0.04 from the host emission lines. However, the
source is clearly detected in the images taken in i-band with WASP.

We thank the staff of the Palomar observatory for facilitating these
observations.

T. Tamura (Kanagawa U),
A. Yoshida, T. Sakamoto, V. Pal'shin, S. Sugita (AGU),
Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN),
Y. Asaoka, S. Ozawa, S. Torii (Waseda U),
Y. Shimizu (Kanagawa U), N. Cannady, M. L. Cherry (LSU),
S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena)
and the CALET collaboration:

At the trigger time of the compact binary merger candidate S190426c,
T0=2019-04-26 15:21:55.337 UTC (The LIGO Scientific Collaboration and
Virgo Collaboration, GCN Circ. 24237
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 ), the high-voltage of the CALET
Gamma-ray Burst Monitor (CGBM) detectors were off
(from T0-19 min to T0+10 min).

The CALET Calorimeter (CAL) was operating in high energy trigger mode
at the trigger time of S190426c. Using the CAL data, we have searched for
gamma-ray events in the 10-100 GeV band within the time interval
T0 +/- 60 sec and found no candidates.
The 90% upper limit of CAL is 2.5x10^-5 erg/cm2/s (10-100 GeV) when
the summed LIGO-Virgo probability reaches 10%.
The CAL FOV was centered at RA=183.0 deg, Dec=-50.9 deg at T0.

The LIGO Scientific Collaboration and the Virgo Collaboration report:


We have re-analyzed LIGO and Virgo data around the time of the compact
binary coalescence (CBC) candidate S190426c (GCN 24237
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 ). Parameter
estimation has been performed using LALInference [1] and a new sky
map, lalinference.fits.gz, is available for retrieval from the
GraceDB event page:

https://gracedb.ligo.org/superevents/S190426c/

For the lalinference.fits.gz skymap, the 90% credible region is 1131
deg2. Marginalized over the whole sky, the a posteriori luminosity
distance estimate is 377 +/- 100 Mpc (a posteriori mean +/- standard
deviation). This is the preferred sky map at this time.

For further information about analysis methodology and the contents
of this alert, refer to the LIGO/Virgo Public Alerts User Guide
<https://emfollow.docs.ligo.org/userguide/>.


[1] Veitch et al. PRD 91, 042003 (2015)

M. J. B. Rosell, Steven Janowiecki, Karl Gebhardt, and J. Craig Wheeler, 
on behalf of the LIGO Hobby-Eberly Telescope Response (LIGHETR) team, 
report the spectroscopic observation of the field of S190426c (GCN 
#24208
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 ) with the VIRUS IFU array. We sampled a prioritized list of 5 
galaxies from the GLADE catalog that overlapped with the LIGO 
probability map and the observable pupil of the HET. The resulting data 
cube covers the wavelength 350 to 550 nm with a resolving power of 750. 
The effective limiting magnitude in the B band was 22 magnitudes. Each 
field is 50x50 arc seconds. We observed, in order, galaxies:
305.064514+47.343445
306.223328+56.174004
310.997894+53.242306
306.510681+55.881222
309.586700+59.537640
We note that 310.997894+53.242306 is a known AGN. We find no obvious 
evidence of an optical transient. A more detailed report of the results 
will be submitted later.

The LIGO Scientific Collaboration and the Virgo Collaboration report:

The updated localization for S190426c (GCN 24277
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 ), lalinference.fits, may
have been unreadable due to a data format issue. We have re-uploaded the
FITS file as LALInference1.fits.gz. This is the preferred sky map at this
time.

Zi-Pei Zhu, Dong Xu, Bang-Yao Yu, Tian-Meng Zhang, Xu Zhou, Xiao-Ming 
Teng, Peng-Fei Liu, Xiang-Nan Guan, Yun-Fei Xu, Dong-Wei Fan, Chen-Zhou 
Cui, Hui-Juan Wang (NAOC), Sheng Yang (INAF-OAPd), Hai-Bin Zhao, Bin Li 
(PMO), Jin-Zhong Liu, Hu-Biao Niu, Jun-Hui Liu, Xuan Zhang (XAO), 
Ji-Rong Mao, Jin-Ming Bai (YNAO), Xing Gao (Urumqi No.1 Senior High 
School) report on behalf of the GWFUNC collaboration:

We selected a bunch of galaxies from the GLADE catalog, which overlap 
with the high probability map of the LIGO GW event S190426c (GCN 24237
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 ) 
and are accessible to the NEXT-0.6m telescope located at Nanshan, 
Xinjiang, China. Due to weather constraint, we obtained ten field images 
with reasonable depth. Observations started at 17:19:27 UT on 2019-04-26 
and ended at 18:40:06 UT on 2019-04-26, with each unfiltered exposure of 
120 sec. Typical limiting depth is of ~18.5 mag.

Below listed are the observed galaxies:

         Galaxy_name  		    R.A.      Dec.
2MASS+00304776+8259011 7.69904 +82.9837
2MASS+20242781+4900526 306.116 +49.0146
2MASS+20334424+5403120 308.434 +54.0533
2MASS+20370886+5756538 309.287 +57.9483
2MASS+20441724+8654219 311.072 +86.9061
2MASS+21044313+8719037 316.18   +87.3177
2MASS+21185927+8522535 319.747 +85.3815
2MASS+23370966+8226215 354.29   +82.4393
2MASS+23440128+8338231 356.005 +83.6398
2MASS+23542829+8425182 358.618 +84.4217

No apparent optical transients are found in the above galaxies.

Michael W. Coughlin (Caltech), Mansi M. Kasliwal (Caltech), Daniel A.
Perley (LJMU), Ariel Goobar (OKC), Leo P. Singer (NASA GSFC), Shreya Anand
(Caltech), Tomas Ahumada (UMD), Igor Andreoni (Caltech), Eric C. Bellm
(UW), K. De (Caltech), R. Biswas (OKC), S. Nissanke (UvA), Dmitry Duev
(Caltech), S. Bradley Cenko (NASA GSFC), D. Goldstein (Caltech), A. Ho
(Caltech), V. Bhalerao (IITB), H. Kumar (IITB), V. Karambelkar (IITB), K.
Deshmukh (IITB), D. Saraogi (IITB), G. C. Anupama (IIA), C. Copperwheat
(LJMU), Virginia Cunningham (UMD), Shaon Ghosh (UWM), David Kaplan (UWM),
Jesper Sollerman (OKC), Joshua S. Bloom (UCB), M. Bulla (OKC), Matthew
Graham (Caltech), L. Yan (Caltech), C. Fremling (Caltech), Pradip Gatkine
(UMD), A. Miller (Northwestern)

On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of
Observatories Watching Transients Happen (GROWTH) collaborations

We observed the localization region of the gravitational wave trigger
S190426c (GCN 24237
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 ) with the Palomar 48-inch telescope equipped with the
47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). A new
tiling was automatically optimally determined and triggered using the
GROWTH Target of Opportunity marshal (Coughlin et al. 2019a, Kasliwal et
al. 2019b). We started obtaining target-of-opportunity observations in the
g-band and r-band filters beginning at UT 2019-04-27 05:45. The projected
enclosed probability with the original sky map was 75%. However, with the
new sky map (GCN 24277
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 , GCN 24279
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 ) and taking account into chip gaps and
processing, a total of 4340 square degrees covering 55% of the enclosed
probability were observed before 12-deg twilight and analyzed in real-time.
Exposure length varied between 120s, 180s and 300s. We note that the area
around the north celestial pole covered by our partner GROWTH-India
telescope covers an additional 6% of the updated probability map,
complementary to ZTF (see GCN 24258
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 ).

The images were processed through the ZTF reduction and image subtraction
pipelines at IPAC to search for potential counterparts (Masci et al. 2019).
After rejecting stellar sources (Tachibana and Miller 2018) and moving
objects and applying machine learning algorithms (Mahabal et al. 2019),
several high-significance transient candidates were identified by our
pipeline in the area observed. Thanks to the overlap in sky maps between
the two GW triggers S190426c and S190425z, we have very good constraints on
past history of variability in the last few days.

The only candidate with the first detection after the merger time is:

-----------------------------------------------------------------------------------------------
 ZTF Name     | RA (deg)    | DEC (deg)   | Filter | Mag   |  Magerr |
Filter| Mag   | Magerr
--------------+-------------+-------------+--------+-------+---------+-------+-------+---------
ZTF19aaslzfk  | 308.968271  | 72.3536353  | r      | 20.91 |  0.17   | g
  | 21.38 |  0.18
-----------------------------------------------------------------------------------------------

We caution that our upper limits in the last few days for ZTF19aaslzfk are
shallower than the detection. So we cannot rule out an old, unrelated
transient. The line-of-sight extinction is Ar of 1.4 mag (Schlafly et al.
2011). We note that the source is detected in all four WISE filters in the
AllWISE catalog (Wright et al. 2010).  Its W1-W3 colors are intermediate
between galaxies and AGN relative to the color loci of Assef et al. (2018),
but the clear W4 detection suggests contribution from an active galactic
nucleus.

Additional analysis and continued follow-up is in progress.

ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC,
USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY,
Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan;
IIT-B, India; IIA, India; LJMU, UK; TTU, USA; and USyd, Australia. ZTF
acknowledges the generous support of the NSF under AST MSIP Grant No
1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant
No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et
al. 2019). Alert filtering and follow-up co-ordination is being undertaken
by the GROWTH marshal system (Kasliwal et al. 2019).

M. Hankins (Caltech), K. De (Caltech), M. Coughlin (Caltech), M. M.
Kasliwal (Caltech), S. M. Adams (Caltech), I. Andreoni (Caltech), S.
Anand (Caltech), L. Singer (NASA GSFC), T. Ahumada (UMD),  A. Moore
(ANU), J. Soon (ANU), M. Ashley (UNSW), T. Travouillon (ANU)

report on behalf of the Palomar Gattini-IR team and the larger GROWTH
(Global Relay of Observatories Watching Transients Happen)
collaboration

We report wide-field near-infrared follow-up observations of the
localization region of the gravitational wave event S190426c (GCN
#24237
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 ) by the Palomar Gattini-IR survey (Moore and Kasliwal 2019).
Gattini-IR is a newly commissioned near-IR camera with a field of view
of 25 square degrees mounted on a robotic 30 cm telescope at Palomar
observatory.

We started customized Target of Opportunity observations at UT
2019-04-27 03:31. The tiling was optimally determined and triggered
using the GROWTH Target of Opportunity marshal (Coughlin et al. 2019a,
Kasliwal et al. 2019b). We imaged a total of 2200 square degrees,
covering 92% of the probability region of the event for 1 to 4 epochs
until UT 2019-04-27 13:21. Each field visit consisted of a sequence of
8 dithers of 8 second exposures each on the field, which were
processed and stacked with the Palomar Gattini-IR data reduction
pipeline (De et al., in prep.). The typical limiting magnitude of each
stacked epoch (64 second exposure time) was between 14.5 and 15 AB mag
in J-band, and shallower than usual due to poor weather conditions.
Transient vetting is ongoing and any viable counterparts will be
announced.

Bin Li, Hai-bin Zhao (PMO), Dong Xu, Zi-pei Zhu, Bang-yao Yu, Tian-meng 
Zhang, Xu Zhou, Chen-zhou Cui, Hui-juan Wang (NAOC), Xue-feng Wu, 
Zhi-ping Jin, Tian-rui Sun, Hao Lu, Ge-tu Zhaori, Ren-quan Hong, 
Long-fei Hu (PMO), Xiao-feng Wang, Wen-xiong Li (THU), Li-fan Wang 
(PMO/TAMU), Jin-zhong Liu (XAO), Ji-rong Mao, Jin-ming Bai (YNAO) report 
on behalf of the CNEOST collaboration:

We conducted optical imaging observations for gravitational wave alert 
with Chinese Near Earth Object Survey Telescope (CNEOST) at Xuyi 
astronomical station in Jiangsu Province, China (32.75N, 118.47E). The 
information of observations and preliminary results are listed below.

Alert: LIGO/Virgo S190426c (GCN 24237
Loading...
 
 )
StartTime (UT):               2019-04-26T16:38:56.981
EndTime (UT):                 2019-04-26T20:07:36.183
Skycover (Square Degree):     774.0
Telescope FoV (Square Degree):9.0
#  id  FoV_CentRA(Deg)  FoV_CentDEC(Deg) LimiteMag3\sigma 5\sigma 
10\sigma  Filter
       1    280.820160     85.517708      20.667      19.595      18.319 
      VR
       2    315.430237     85.439629           -           -           - 
      VR
       3    349.655731     85.372475           -           -           - 
      VR
       4      0.272468     85.374985      20.421      19.412      18.049 
      VR
       5    348.235748     82.581619      20.467      19.409      18.071 
      VR
       6    326.778412     82.607399           -           -           - 
      VR
       7    305.197693     82.690369           -           -           - 
      VR
       8    283.561981     82.690361           -           -           - 
      VR
       9    280.820160     85.517708      20.667      19.595      18.319 
      VR
      10    315.430237     85.439629           -           -           - 
      VR
      11    349.655731     85.372475           -           -           - 
      VR
      12      0.272468     85.374985      20.421      19.412      18.049 
      VR
      13    348.235748     82.581619      20.467      19.409      18.071 
      VR
      14    326.778412     82.607399           -           -           - 
      VR
      15    305.197693     82.690369           -           -           - 
      VR
      16    283.561981     82.690361           -           -           - 
      VR
      17    280.820160     85.517708      20.667      19.595      18.319 
      VR
      18    315.430237     85.439629           -           -           - 
      VR
      19    349.655731     85.372475           -           -           - 
      VR
      20      0.272468     85.374985      20.421      19.412      18.049 
      VR
      21    348.235748     82.581619      20.467      19.409      18.071 
      VR
      22    326.778412     82.607399           -           -           - 
      VR
      23    305.197693     82.690369           -           -           - 
      VR
      24    283.561981     82.690361           -           -           - 
      VR
      25    319.178864     74.233849      20.685      19.654      18.534 
      VR
      26    324.038544     77.046799      20.603      19.549      18.370 
      VR
      27    311.633820     77.040756      20.651      19.597      18.336 
      VR
      28    316.798065     79.851402      20.538      19.540      18.278 
      VR
      29    332.518555     79.810440           -           -           - 
      VR
      30    348.177490     79.773155           -           -           - 
      VR
      31    348.773438     76.988274      20.251      19.286      18.005 
      VR
      32    336.383240     77.012527      20.530      19.461      18.209 
      VR
      33    339.602112     74.196800      20.347      19.336      18.174 
      VR
      34    329.386444     74.234039      20.458      19.428      18.281 
      VR
      35    319.178864     74.233849      20.685      19.654      18.534 
      VR
      36    324.038544     77.046799      20.603      19.549      18.370 
      VR
      37    311.633820     77.040756      20.651      19.597      18.336 
      VR
      38    316.798065     79.851402      20.538      19.540      18.278 
      VR
      39    332.518555     79.810440           -           -           - 
      VR
      40    348.177490     79.773155           -           -           - 
      VR
      41    348.773438     76.988274      20.251      19.286      18.005 
      VR
      42    336.383240     77.012527      20.530      19.461      18.209 
      VR
      43    339.602112     74.196800      20.347      19.336      18.174 
      VR
      44    329.386444     74.234039      20.458      19.428      18.281 
      VR
      45    319.178864     74.233849      20.685      19.654      18.534 
      VR
      46    324.038544     77.046799      20.603      19.549      18.370 
      VR
      47    311.633820     77.040756      20.651      19.597      18.336 
      VR
      48    316.798065     79.851402      20.538      19.540      18.278 
      VR
      49    332.518555     79.810440           -           -           - 
      VR
      50    336.383240     77.012527      20.530      19.461      18.209 
      VR
      51    299.525238     46.251789      20.401      19.480      18.006 
      VR
      52    311.657715     46.230133      20.250      19.320      17.684 
      VR
      53    304.592407     43.480080      20.410      19.500      18.255 
      VR
      54    302.534668     40.635784      20.422      19.507      17.783 
      VR
      55    311.936005     37.808170      20.186      19.251      17.812 
      VR
      56    301.344299     37.860779      20.372      19.498      17.506 
      VR
      57    300.906097     35.026001      20.290      19.387      17.618 
      VR
      58    307.813385     32.240044      20.193      19.273      18.032 
      VR
      59    297.888336     32.272041      20.199      19.359      17.442 
      VR
      60    302.225403     29.456776      20.353      19.436      18.201 
      VR
      61    306.943420     26.630651      20.129      19.248      17.940 
      VR
      62    297.592102     26.692783      20.381      19.452      17.974 
      VR
      63    303.023682     23.862503      20.257      19.336      17.940 
      VR
      64    297.782227     18.269867      20.261      19.334      17.345 
      VR
      65    299.220764     15.473767      20.075      19.172      17.501 
      VR
      66    298.443146     12.670787      19.969      19.078      17.526 
      VR
      67    296.242340      7.066733      19.988      19.091      17.686 
      VR
      68    314.732300     63.022617      20.353      19.402      18.339 
      VR
      69    311.992279     57.445961      20.423      19.495      18.441 
      VR
      70    309.506592     54.678425      20.287      19.374      18.141 
      VR
      71    311.713623     49.022232      20.455      19.516      18.160 
      VR
      72    303.515625     51.858234      20.357      19.434      17.994 
      VR
      73    306.784424     57.462719      20.414      19.480      18.313 
      VR
      74    308.590790     63.066647      20.359      19.407      18.222 
      VR
      75    310.045654     60.261044      20.435      19.493      18.319 
      VR
      76    314.339447     54.666424      20.478      19.538      18.500 
      VR
      77    312.579285     51.856945      20.420      19.500      18.288 
      VR
      78    303.160950     49.069408      20.422      19.490      18.076 
      VR
      79    301.595581     57.451702      20.377      19.413      18.106 
      VR
      80    302.417633     63.046188      20.313      19.381      18.075 
      VR
      81    315.717224     60.247940      20.431      19.481      18.476 
      VR
      82    317.155365     57.423546      20.405      19.476      18.382 
      VR
      83    308.046173     51.860016      20.336      19.460      18.051 
      VR
      84    307.452972     49.037590      20.331      19.418      18.011 
      VR
      85    304.680237     54.659714      20.349      19.443      18.070 
      VR
      86    304.424927     60.269768      20.302      19.374      18.127 
      VR

Detailed data analysis is still in progress and any interesting 
transients will be reported later.

WeiKang Zheng, Keto Zhang, Sergiy Vasylyev and Alexei V. Filippenko
(UC Berkeley) report on behalf of the Lick/KAIT GW follow-up team:

The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, observed the field of the gravitational-wave event
S190426c (GCN 24237
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 ) detected by LIGO/Virgo. More than one thousand
galaxies were selected from the Glade catalog V1.0 (Dalya et al.,
2018, MNRAS, 479, 2374; http://aquarius.elte.hu/glade/)
according to their priority score. KAIT observed 247 of them based on
their priority scores and elevation visibility, with each clear-filter
exposure time being 60 s. The first image was taken at 03:58:26, Apr. 27 UT,
about 12.6 hours after the trigger, and the last image at 11:38:50 UT.
Our typical limiting mag is 19.0. A transient was found in G1148595 (aka
NGC3362), which was known as SN 2019cda. No other viable counterparts
were identified and the analysis is ongoing. A full list of galaxies
observed by KAIT is given below.

GladeID  UT(Apr. 27)  RA (J2000)   Dec
-----------------------------------------------
G0183894  063314  11:11:53.490  -04:33:31.80
G0272256  060809  11:08:11.380  -01:37:58.30
G0395642  055233  12:11:00.490  -19:50:38.30
G0489265  040522  10:57:01.750  +02:24:28.60
G0548994  064600  11:12:59.190  -04:27:10.80
G0549630  084459  10:56:32.400  +08:44:36.20
G0553090  042510  11:03:11.040  -04:36:10.70
G0553090  080135  11:03:10.750  -04:36:10.60
G0553620  042031  11:02:58.740  +00:33:17.10
G0553620  075807  11:02:58.400  +00:33:17.00
G0553862  045632  10:49:11.720  +04:49:32.20
G0559959  090350  11:00:20.520  -07:05:55.70
G0562511  040631  10:58:31.320  +05:35:42.90
G0562677  045523  10:49:08.820  +04:51:46.80
G0565110  045414  10:48:48.930  +01:00:53.80
G0565949  090130  11:00:05.390  +01:04:42.00
G0566631  054903  11:55:27.330  -16:15:45.90
G0570385  072941  11:20:38.980  -08:36:52.50
G0572117  055741  11:07:17.360  -06:07:31.80
G0572117  080831  11:07:17.190  -06:07:32.20
G0572503  064451  11:12:47.450  -07:37:53.20
G0572760  052229  11:27:11.150  -11:15:14.60
G0573430  064341  11:12:47.060  -04:26:05.10
G0574754  044933  10:46:09.960  +04:50:34.20
G0575991  072611  11:19:32.690  -07:55:54.80
G0579510  045741  10:49:11.840  +04:53:44.80
G0580598  072022  11:18:54.000  -02:03:06.40
G0580886  085754  10:59:26.990  +04:06:52.60
G0585606  091828  11:36:28.050  -09:57:37.80
G0587735  035826  10:52:48.900  +03:40:35.60
G0587735  075328  10:52:48.950  +03:40:35.90
G0590130  062423  11:10:19.390  -00:57:29.70
G0590201  044006  10:40:04.890  +04:32:48.50
G0590201  051538  10:40:04.750  +04:32:48.60
G0590484  061357  11:08:36.810  -00:07:54.90
G0590484  082002  11:08:36.760  -00:07:54.30
G0590830  070000  11:15:38.320  -06:52:47.50
G0593995  044451  10:45:30.730  +02:15:52.80
G0594030  053141  11:40:29.620  -14:18:37.10
G0594729  052120  11:22:53.250  -10:35:01.20
G0596108  042950  11:05:19.920  -06:36:39.00
G0601147  053032  11:39:24.280  -13:11:22.80
G0606812  062314  11:10:19.570  -00:13:13.60
G0609002  052704  11:38:21.850  -13:16:55.90
G0609034  074336  11:24:39.240  -09:32:17.10
G0609179  085310  10:58:51.020  +07:56:26.20
G0609910  084938  10:57:46.520  +06:45:00.90
G0612118  052338  11:29:23.350  -11:28:41.20
G0612394  041222  11:00:13.940  -00:47:46.70
G0614729  041810  11:02:28.040  -04:22:26.50
G0614729  075546  11:02:27.830  -04:22:25.90
G0614900  063902  11:12:06.930  -06:42:07.50
G0616501  083537  10:52:57.090  -01:37:27.70
G0617323  060331  11:07:38.320  -01:35:59.60
G0617323  081306  11:07:38.250  -01:36:00.50
G0618318  041112  10:59:56.520  +01:20:00.40
G0623013  073859  11:23:26.420  -05:18:02.40
G0624899  040154  10:55:57.210  +00:20:57.30
G0626343  055850  11:07:28.740  -02:49:38.70
G0626343  080940  11:07:28.510  -02:49:38.50
G0626541  073531  11:22:03.470  -09:29:28.80
G0626921  074555  11:25:50.630  -08:54:09.50
G0628200  043526  10:34:54.430  +11:06:24.10
G0628200  051100  10:34:54.450  +11:06:24.50
G0628220  090615  11:01:12.890  -03:11:30.50
G0628851  083909  10:54:50.990  +00:14:02.00
G0632969  061725  11:08:45.040  -01:50:54.90
G0632969  082330  11:08:45.030  -01:50:54.00
G0634233  084129  10:55:43.340  +02:30:32.30
G0634535  074813  11:26:10.620  -09:08:49.70
G0635861  060113  11:07:37.230  -02:45:59.80
G0637766  060222  11:07:37.180  -02:49:25.80
G0637766  081159  11:07:37.280  -02:49:26.10
G0638543  052813  11:39:15.390  -13:31:53.00
G0638671  041442  11:01:32.170  +02:00:42.00
G0638963  073420  11:22:00.000  -04:39:50.60
G0639517  061248  11:08:31.140  +00:40:42.60
G0639517  081853  11:08:31.020  +00:40:41.70
G0640572  074445  11:24:47.290  -08:47:44.60
G0642533  060004  11:07:34.950  -00:48:14.60
G0642533  081050  11:07:35.010  -00:48:14.90
G0643033  064819  11:13:14.100  -05:51:32.60
G0643853  063423  11:11:57.340  -03:40:42.90
G0643892  045042  10:47:24.260  +07:28:55.80
G0644398  061139  11:08:28.370  +03:41:51.40
G0648171  040852  10:59:33.480  -04:26:35.90
G0648835  083316  10:52:30.000  +09:10:35.60
G0651799  073750  11:22:40.810  -04:38:37.00
G0652133  062904  11:10:55.840  -04:34:46.00
G0653686  070218  11:16:15.630  -05:25:05.10
G0655620  040303  10:56:03.430  -01:11:56.90
G0656169  090241  11:00:15.530  -03:38:13.20
G0656942  072243  11:19:28.640  -09:43:43.60
G0657266  085050  10:58:30.470  +00:41:51.90
G0657990  050915  10:52:14.890  +02:20:05.00
G0662103  042838  11:04:49.470  -00:42:22.80
G0662103  080503  11:04:49.340  -00:42:22.60
G0662104  070439  11:16:56.960  -02:16:34.90
G0662185  074227  11:24:02.990  -10:02:57.30
G0663137  085422  10:58:59.070  -03:11:54.10
G0663945  041001  10:59:38.490  -03:36:29.50
G0664356  084608  10:56:32.340  +04:21:00.90
G0666774  043855  10:39:38.940  +11:06:59.60
G0666774  051426  10:39:39.340  +11:07:00.80
G0668963  084239  10:55:58.800  +01:16:59.60
G0670041  084348  10:55:59.910  -00:52:07.50
G0670285  044340  10:44:31.400  +10:52:36.90
G0670531  050328  10:49:47.930  +04:12:16.50
G0671170  063530  11:11:59.740  -04:25:48.90
G0672325  060441  11:07:42.350  -04:50:51.60
G0672325  081416  11:07:42.330  -04:50:51.90
G0673700  050219  10:49:47.260  +04:12:49.20
G0675153  073640  11:22:37.580  -06:28:58.70
G0676039  050656  10:51:04.980  +01:41:47.50
G0676486  045151  10:47:34.530  +04:00:38.50
G0679815  040045  10:55:21.640  -00:28:06.50
G0681167  042140  11:03:02.320  +03:28:33.30
G0681402  063640  11:11:58.860  -08:08:07.40
G0681509  085644  10:59:12.510  +07:28:05.80
G0682016  061834  11:08:53.780  -05:06:34.60
G0682016  082439  11:08:53.790  -05:06:34.60
G0682408  072501  11:19:32.180  -04:30:05.20
G0682877  053251  11:40:46.570  -14:44:24.40
G0685235  062755  11:10:45.720  +00:42:30.90
G0685620  045851  10:49:24.330  +05:10:02.90
G0688162  052448  11:35:09.580  -10:50:21.50
G0688773  054207  11:43:16.740  -11:58:29.10
G0692183  055452  12:15:02.740  -18:39:13.00
G0697713  070548  11:17:12.200  -05:23:54.70
G0697935  040740  10:59:10.690  +01:30:04.50
G0698912  062532  11:10:19.430  -00:32:44.50
G0702659  053947  11:42:21.260  -17:40:25.50
G0704552  074923  11:27:34.250  -08:21:24.90
G0704844  043636  10:36:25.050  +07:26:46.50
G0704844  051209  10:36:25.120  +07:26:47.40
G0705327  054426  11:48:24.070  -16:44:03.50
G0707027  054058  11:42:30.220  -12:29:41.00
G0707360  063014  11:11:32.850  -00:41:17.40
G0711373  063751  11:11:59.750  -00:59:54.00
G0712402  071652  11:17:12.550  -06:35:08.10
G0714524  041331  11:01:19.740  -05:06:42.40
G0716604  054644  11:54:02.060  -16:29:25.20
G0716777  050109  10:49:44.020  +07:09:13.20
G0716998  044229  10:42:15.900  +04:47:08.40
G0717672  053619  11:41:58.330  -12:30:19.30
G0719909  043745  10:38:53.610  +10:39:26.70
G0719909  051319  10:38:53.630  +10:39:26.70
G0725542  035935  10:53:53.400  -00:47:07.90
G0729766  054535  11:52:35.920  -16:26:03.80
G0733916  084020  10:55:26.470  +07:02:24.10
G0734402  090724  11:01:25.540  -03:23:12.90
G0737008  042401  11:03:07.050  -03:46:44.70
G0737008  080026  11:03:06.880  -03:46:44.80
G0737866  085905  10:59:28.100  -05:47:35.20
G0738123  050547  10:51:00.990  +04:51:35.50
G0739133  075032  11:28:14.430  -06:19:19.30
G0739740  044714  10:45:50.130  +02:56:54.90
G0739801  064121  11:12:15.250  -06:22:20.70
G0740064  074704  11:26:07.180  -06:36:26.10
G0740915  064232  11:12:16.140  -00:55:46.90
G0741452  052923  11:39:21.050  -12:03:47.50
G0743465  090504  11:00:33.350  +07:34:48.40
G0743638  064012  11:12:13.590  -06:24:54.60
G0743790  083759  10:53:29.850  -00:46:10.00
G0747080  084720  10:56:59.340  -01:03:28.80
G0751074  040412  10:56:19.420  -01:02:49.80
G0754612  044603  10:45:36.770  +11:11:38.50
G0755412  043101  11:06:35.450  +00:46:22.40
G0755412  080612  11:06:35.560  +00:46:23.80
G0756145  053509  11:41:52.100  -10:49:50.90
G0756454  072133  11:19:22.100  -07:13:06.50
G0763402  084829  10:57:33.990  +03:17:43.60
G0764514  061027  11:08:16.820  -02:03:21.50
G0764514  081743  11:08:16.780  -02:03:21.30
G0765819  060550  11:07:44.430  -04:10:38.00
G0766381  052557  11:36:28.270  -12:27:08.60
G0769870  072829  11:20:25.560  -03:31:04.30
G0770090  061616  11:08:44.210  -02:20:19.00
G0770090  082221  11:08:44.150  -02:20:18.90
G0770692  042729  11:04:03.530  -04:14:39.50
G0770692  080354  11:04:03.500  -04:14:39.40
G0777282  044119  10:40:59.690  +03:00:39.80
G0777282  051647  10:40:59.810  +03:00:40.30
G0777485  060918  11:08:15.420  -02:04:25.90
G0777485  081634  11:08:15.440  -02:04:25.00
G0778169  065146  11:13:35.480  -03:19:01.10
G0779011  041552  11:01:48.900  +00:17:44.50
G0781665  054316  11:44:43.320  -13:24:11.40
G0782431  061506  11:08:41.020  -03:17:10.80
G0782431  082111  11:08:41.090  -03:17:10.50
G0782924  050805  10:51:32.370  +00:39:01.70
G0785186  074008  11:23:38.550  -10:20:51.70
G0786363  041701  11:02:21.410  -01:14:39.40
G0786363  075437  11:02:21.420  -01:14:38.70
G0786634  055124  12:10:47.060  -19:08:09.60
G0790178  062053  11:09:29.050  -03:44:26.80
G0790178  082658  11:09:28.860  -03:44:27.40
G0791742  073159  11:21:26.650  -07:28:36.70
G0792779  050437  10:50:02.100  +02:46:50.70
G0796085  065256  11:14:03.010  -03:23:20.70
G0796285  053728  11:42:06.470  -12:50:31.60
G0797419  060659  11:07:44.820  -01:13:49.00
G0797419  081525  11:07:45.030  -01:13:49.60
G0798730  053400  11:41:01.030  -12:46:37.60
G0798801  072720  11:19:35.450  -04:54:41.60
G0800890  083427  10:52:45.910  +02:48:19.50
G0804096  071802  11:17:47.010  -08:22:50.80
G0805699  071913  11:17:58.550  -01:20:35.20
G0806101  045302  10:47:39.970  +11:39:46.30
G0807574  083648  10:53:08.290  +04:57:22.10
G0810723  065850  11:15:38.120  -05:24:44.00
G0811304  053835  11:42:17.440  -12:49:54.30
G0815282  090018  10:59:59.410  +06:25:06.40
G0822175  055631  11:06:37.290  -03:30:16.00
G0822175  080722  11:06:37.450  -03:30:14.20
G0822865  085533  10:59:05.490  +02:17:08.60
G0823787  085201  10:58:31.270  +06:33:23.10
G0845933  065741  11:15:30.800  -05:33:26.30
G0867712  091938  11:38:50.060  -09:28:51.20
G0915032  055012  12:00:03.340  -17:08:02.60
G0932849  055342  12:14:16.220  -19:20:41.40
G0958433  073308  11:21:39.860  -09:57:45.50
G0965443  064709  11:12:59.870  -06:50:25.90
G0979304  041922  11:02:38.370  +01:18:33.20
G0979304  075658  11:02:38.200  +01:18:33.40
G1032288  061944  11:09:16.340  -05:14:13.40
G1032288  082549  11:09:16.330  -05:14:13.00
G1052029  065521  11:14:36.820  -02:03:39.60
G1070206  070109  11:15:41.100  -03:55:12.30
G1086865  065632  11:15:11.260  -07:00:17.20
G1126327  070328  11:16:55.520  -07:23:22.60
G1148595  044823  10:45:51.860  +06:29:41.60
G1276417  072352  11:19:29.230  -06:28:55.00
G1278481  073050  11:20:50.830  -04:36:27.80
G1279248  074118  11:23:52.390  -09:07:42.10
G1342028  054754  11:54:24.840  -16:03:20.80
G1377676  075141  11:28:44.080  -06:55:21.00
G1420214  062202  11:09:54.380  -06:17:49.50
G1437959  065037  11:13:29.430  -06:04:50.20
G1640464  042620  11:03:13.500  -01:12:28.10
G1640464  080244  11:03:13.420  -01:12:28.10
G1642067  050000  10:49:42.600  +04:11:20.10
G1642147  065411  11:14:19.640  +02:26:29.00
G1642887  042251  11:03:03.470  -02:33:25.10
G1642887  075917  11:03:03.390  -02:33:26.10
G1645440  064928  11:13:22.450  -03:18:12.90
G1667542  062642  11:10:34.290  -03:46:19.10

[GCN OPS NOTE(27apr19): Per author's request, the "observed XXX" was changed to "observed 247".]

D.Steeghs(1), J.Lyman(1), M.Dyer(3), D.Galloway(2), V.Dhillon(3),
P.O'Brien(4), G.Ramsay(5), D.Pollacco(1), E.Thrane(2),
S.Poshyachinda(6), E.Palle(7), K.Ulaczyk(1), R.Cutter(1),
A.Levan(1), T. Marsh(1), R.West(1), K.Wiersema(1), B.Gompertz(1),
E.Stanway(1), K.Ackley(2), A.Obradovic(2), Y-L.Mong(2), A.Casey(2),
M.Brown(2), E.Rol(2), J.Mullaney(3), S.Littlefair(3),
L.Makrygianni(3), E.Daw(3), J.Maund(3), R.Starling(4), R.Eyles(4),
U.Sawangwit(6), D.Mkrtichian(6), S.Awiphan(6),S.Aukkaravittayapun(6),
P.Irawati(6), M.Kennedy(8), R.Breton(8), D.Mata-Sanchez(8),
T.Heikkila(9), R.Kotak(9)
(1) Warwick University; (2) Monash University; (3) Univ. of Sheffield;
(4) University of Leicester; (5) Armagh Observatory;
(6) National Astronomical Research Institute of Thailand;
(7) Instituto de Astrofisica de Canarias; (8) Univ. of Manchester;
(9) University of Turku

report on behalf of the GOTO collaboration:

We report on optical observations with the Gravitational-wave Optical
Transient Observer in response to event S190426c (GCN #24237
Loading...
 
 ).

Targeted observations across 49 pointings containing 54.1% of the
source location probability across 755 sqr. degrees (based on the
updated LALInference skymap, GCN #24279
Loading...
 
 ) were performed between 20:38
UT Apr 26 and 05:32 UT Apr 27 2019.

A small number of fields were affected by having limited quality
survey reference frames available and the area includes dense low
galactic latitude fields. We recover a number of known/already reported
transients and many foreground variable objects, but no significant
detections of new candidates that could be credibly associated with
S190426c.

Each pointing spans 4.9x3.7 square degrees and consisted of 3x60s
exposures in our L-band filter (400-700nm passband) with typical
5-sigma photometric depth of g=19.9, based on a photometric
calibration against PS1 sources. A coverage map is available at
http://goto-observatory.warwick.ac.uk/S190426c.html

Images are processed immediately after acquisition using the GOTOphoto
pipeline. Difference imaging was performed on the median of each
triplet of exposures using recent survey observations of the same
pointings. Source candidates were initially filtered using a
classifier and cross-matched against a variety of catalogs, including
the MPC and  PS1. Human candidate vetting was performed during data
acquisition and processing in case of notable detections.


GOTO is operated at the La Palma observing facilities of the
University of Warwick on behalf of a consortium including the
University of Warwick, Monash University, Armagh Observatory, the
University of Leicester, the University of Sheffield, the National
Astronomical Research Institute of Thailand (NARIT) and the Instituto
de Astrofisica de Canarias (IAC) (https://goto-observatory.org/)

G. Hosseinzadeh, S. Gomez, L. Patton, E. Berger, P. K. Blanchard,
T. Eftekhari, J. Gill, V. A. Villar, P. K. G. Williams (Harvard U),
P. S. Cowperthwaite (Carnegie Obs), R. Chornock (Ohio U), W. Fong, 
R. Margutti (Northwestern U), and M. Nicholl (U Edinburgh) report:

We obtained 30 s i-band images of the following GLADE galaxies (Dalya
et al. 2018, MNRAS, 479, 2374) in the LIGO/Virgo localization region of
S190426c (GCN 24237
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 ) with the MMTCam instrument on the MMT 6.5-m telescope:

Name              R.A.        Dec.       Date        UT
18191810+8807285  274.825439  88.124603  2019-04-27  08:38:51.40
18215068+8642223  275.461182  86.706215  2019-04-27  08:40:44.16
18242867+8642139  276.119476  86.703888  2019-04-27  08:42:02.29
19301513+8540516  292.563049  85.681000  2019-04-27  08:44:01.04
20412914+8626330  310.371429  86.442513  2019-04-27  08:47:15.62
20441724+8654219  311.071838  86.906105  2019-04-27  08:48:44.73
3085923           313.123840  86.186646  2019-04-27  08:50:06.79
20452666+8620428  311.361084  86.345238  2019-04-27  08:53:22.23
20592695+8454369  314.862305  84.910271  2019-04-27  08:55:00.27
20110295+4637149  302.762329  46.620808  2019-04-27  09:00:55.59
20113931+4550035  302.913818  45.834320  2019-04-27  09:03:02.52
20114858+4657335  302.952423  46.959324  2019-04-27  09:04:39.00
20132761+4630313  303.365082  46.508705  2019-04-27  09:06:17.34
20134502+4726333  303.437622  47.442604  2019-04-27  09:07:51.07
20152058+4555282  303.835785  45.924526  2019-04-27  09:09:30.54
20201548+4720364  305.064514  47.343445  2019-04-27  09:12:40.37
20242781+4900526  306.115875  49.014629  2019-04-27  09:14:19.34
20354336+4953165  308.930695  49.887932  2019-04-27  09:15:46.70
20224302+5636145  305.679291  56.604050  2019-04-27  09:17:53.43
20244336+5245430  306.180695  52.761951  2019-04-27  09:19:32.34
20245359+5610264  306.223328  56.174004  2019-04-27  09:20:53.09
20260256+5552523  306.510681  55.881222  2019-04-27  09:22:19.39
20273404+5015483  306.891846  50.263424  2019-04-27  09:23:52.13
20273859+5353393  306.910797  53.894264  2019-04-27  09:25:23.97
20281516+5641284  307.063202  56.691227  2019-04-27  09:26:51.40
20290191+5817016  307.257996  58.283779  2019-04-27  09:28:13.83
20291160+5219510  307.298340  52.330837  2019-04-27  09:29:55.67
20300804+5415120  307.533508  54.253361  2019-04-27  09:31:48.43
20304675+6259395  307.694824  62.994316  2019-04-27  09:37:44.30
20322187+5812031  308.091156  58.200874  2019-04-27  09:39:26.33
20334424+5403120  308.434357  54.053345  2019-04-27  09:41:06.11
20334533+6254178  308.438904  62.904968  2019-04-27  09:42:45.02
20352447+5759548  308.851959  57.998581  2019-04-27  09:44:34.03
20354995+6208172  308.958160  62.138115  2019-04-27  09:47:16.72
20355212+5549587  308.967194  55.832996  2019-04-27  09:49:52.60
20370886+5756538  309.286957  57.948280  2019-04-27  09:51:23.64
20373532+5628217  309.397186  56.472702  2019-04-27  09:52:50.88
20384775+6128473  309.698975  61.479832  2019-04-27  09:54:43.33
20385946+5351220  309.747772  53.856125  2019-04-27  09:56:30.10
20391360+6454369  309.806671  64.910263  2019-04-27  09:58:12.37
20404068+6437003  310.169525  64.616753  2019-04-27  09:59:56.03
20431546+5424171  310.814453  54.404751  2019-04-27  10:02:35.77
20450027+6441410  311.251160  64.694733  2019-04-27  10:04:16.29
20452857+6332249  311.369080  63.540272  2019-04-27  10:05:41.40
20453196+6157519  311.383179  61.964432  2019-04-27  10:07:11.51
20482612+6414178  312.108856  64.238281  2019-04-27  10:08:31.27
20492307+6412331  312.346161  64.209221  2019-04-27  10:10:38.44
20495907+6207478  312.496155  62.129963  2019-04-27  10:12:07.42
20515127+6309235  312.963654  63.156536  2019-04-27  10:13:43.40
20581565+6217178  314.565247  62.288288  2019-04-27  10:15:27.92

Comparison of the images to the PS1 3pi survey (Chambers et al. 2016, 
arXiv:1612.05560
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 ) reveals no new sources brighter than ~21 mag within
the 2.7 arcmin field of view.

We thank Chun Ly and Ben Kunk at MMT for taking these observations and
Dallan Porter for help with the target submission.

Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Nat Butler (ASU),
Eleonora Troja (GSFC/UMD), Simone Dichiara (UMD), Diego Gonz��lez (UNAM),
Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Margarita Pereyra
(UNAM), and Tanner Wolfram (ASU) report:

We observed 98 galaxies selected from the NED/CLU list for LIGO/Virgo
S190426c (Chatterjee et al, GCN Circ. 24237
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 ) with the COATLI 50-cm
telescope and interim imager at the Observatorio Astron��mico Nacional on
the Sierra de San Pedro M��rtir (http://coatli.astroscu.unam.mx) on the
night of 2019-04-27 UTC. For each galaxy, we typically obtained 150
seconds of exposure in the w filter and obtained a typical 10-sigma
limiting magnitude of 19.5. Our observations are listed below. Visual
inspection reveals no obvious counterpart candidates.

We thank the COATLI technical team and the staff of the Observatorio
Astron��mico Nacional.

Start (UTC)  00  0RA and Dec (J2000)  Galaxy
2019-04-27 03:38  352.4159  +85.8608  2MASX J23293953+8551387
2019-04-27 03:42  359.6944  +83.1832  MCG +14-01-005
2019-04-27 03:46  344.9978  +88.5296  2MASX J22595902+8831466
2019-04-27 03:50  274.8875  +87.6408  2MASX J18193355+8738264
2019-04-27 03:59  272.7131  +87.6117  2MASX J18105107+8736422
2019-04-27 04:05  263.4949  +88.3113  MCG +15-01-018
2019-04-27 04:13  358.3364  +86.0277  MCG +14-01-004
2019-04-27 04:16  334.1561  +86.9297  2MASX J22163720+8655469
2019-04-27 04:20  346.0840  +86.7498  UGC 12387
2019-04-27 04:24  314.1693  +87.8807  VII Zw 938
2019-04-27 04:28  308.7320  +87.8154  2MASX J20345612+8748562
2019-04-27 04:31  345.8574  +86.7660  UGC 12377
2019-04-27 04:57  275.8067  +86.8905  UGC 11339
2019-04-27 05:02  350.3873  +83.0117  2MASX J23213266+8300409
2019-04-27 05:05  008.0015  +83.2104  2MASX J00320030+8312372
2019-04-27 05:09  012.1694  +83.7556  UGC 00481
2019-04-27 05:12  008.9427  +83.2329  2MASX J00354608+8313586
2019-04-27 05:16  313.5333  +84.0810  UGC 11664 NED01
2019-04-27 05:19  260.0731  +86.7364  UGC 10923 NED02
2019-04-27 06:39  271.6471  +87.8094  UGC 11267
2019-04-27 06:44  268.8382  +87.7292  MCG +15-01-020
2019-04-27 06:48  266.3379  +87.6423  CGCG 370-007
2019-04-27 06:52  259.8809  +86.7384  UGC 10923 NED01
2019-04-27 06:56  343.4309  +81.7412  2MASX J22534338+8144284
2019-04-27 07:00  265.9047  +86.4693  2MASX J17433725+8628095
2019-04-27 07:04  018.9765  +85.1649  CGCG 360-004
2019-04-27 07:07  304.6286  +62.2037  2MASX J20183085+6212133
2019-04-27 07:14  169.1621  -05.6357  LCRS B111406.3-052146
2019-04-27 07:17  306.9895  +62.5326  2MASX J20275744+6231575
2019-04-27 07:21  304.8255  +58.3678  2MASX J20191811+5822039
2019-04-27 07:24  304.2367  +57.0611  2MASX J20165680+5703397
2019-04-27 07:28  305.1467  +56.2499  CGCG 282-003
2019-04-27 07:31  306.7128  +57.3910  2MASX J20265107+5723277
2019-04-27 07:34  309.2900  +60.3766  2MASX J20370963+6022358
2019-04-27 07:38  309.0248  +58.3807  2MASX J20360594+5822504
2019-04-27 07:41  310.0597  +59.5819  2MASX J20401431+5934550
2019-04-27 07:48  309.4146  +57.3066  2MASX J20373949+5718234
2019-04-27 07:51  311.9760  +57.5972  2MASX J20475419+5735501
2019-04-27 07:55  311.7825  +57.5936  4C +57.35
2019-04-27 07:58  312.1427  +57.0269  2MASX J20483420+5701370
2019-04-27 08:01  312.8025  +57.4421  2MASX J20511259+5726315
2019-04-27 08:05  311.4040  +57.5578  2MASX J20453697+5733282
2019-04-27 08:08  312.2525  +57.6652  2MASX J20490061+5739550
2019-04-27 08:11  304.9635  +48.2723  2MASX J20195124+4816205
2019-04-27 08:15  308.2331  +54.5088  UGC 11592
2019-04-27 08:22  309.9248  +59.5971  2MASX J20394194+5935495
2019-04-27 08:26  299.3077  +19.0874  2MASX J19571383+1905142
2019-04-27 08:29  309.7008  +60.6565  2MASX J20384818+6039233
2019-04-27 08:33  301.0079  +19.2880  2MASX J20040188+1917170
2019-04-27 08:36  301.1253  +19.4085  2MASX J20043008+1924304
2019-04-27 08:40  319.1351  +64.0099  2MASX J21163245+6400358
2019-04-27 08:43  309.3741  +61.0047  2MASX J20372983+6100169
2019-04-27 08:47  304.1979  +56.4738  2MASX J20164753+5628258
2019-04-27 08:50  300.7020  +22.4744  V0362 Vul
2019-04-27 08:57  303.7470  +25.3836  2MASX J20145928+2523010
2019-04-27 09:00  308.8950  +55.9269  2MASX J20353480+5555368
2019-04-27 09:04  299.2132  +16.5608  2MASX J19565118+1633389
2019-04-27 09:07  306.7007  +56.5190  2MASX J20264814+5631084
2019-04-27 09:10  311.3915  +57.0962  2MASX J20453392+5705462
2019-04-27 09:14  305.3853  +49.7603  2MASX J20213251+4945372
2019-04-27 09:17  298.8340  +18.3959  2MFGC 15201
2019-04-27 09:21  314.8096  +58.6364  2MASX J20591430+5838107
2019-04-27 09:24  309.0573  +63.7399  UGC 11603
2019-04-27 09:30  308.8765  +59.2313  2MASX J20353036+5913528
2019-04-27 09:35  314.7172  +57.6427  2MASX J20585215+5738335
2019-04-27 09:39  309.3163  +59.8381  2MASX J20371593+5950168
2019-04-27 09:44  303.4031  +64.4171  2MASX J20133671+6425013
2019-04-27 09:48  304.1438  +26.9762  2MASX J20163450+2658344
2019-04-27 09:51  304.6728  +59.4700  MCG +10-29-002
2019-04-27 09:55  301.6173  +18.5862  2MFGC 15313
2019-04-27 09:58  300.9117  +21.5433  2MASX J20033878+2132359
2019-04-27 10:04  310.3060  +63.5107  UGC 11616
2019-04-27 10:09  313.9236  +69.7426  2MASX J20554160+6944333
2019-04-27 10:12  305.4690  +57.5173  2MASX J20215255+5731021
2019-04-27 10:17  302.5725  +48.0059  2MASX J20101740+4800214
2019-04-27 10:21  304.1962  +25.6489  2MASX J20164708+2538564
2019-04-27 10:24  305.1636  +49.7551  2MFGC 15467
2019-04-27 10:28  303.7108  +63.5932  2MASX J20145058+6335356
2019-04-27 10:31  310.9155  +57.6082  2MASX J20433966+5736291
2019-04-27 10:37  313.2613  +66.4034  VII Zw 937
2019-04-27 10:41  308.1690  +60.0050  2MASX J20324060+6000181
2019-04-27 10:44  253.3640  +86.5912  UGC 10740
2019-04-27 10:48  304.1095  +50.2973  2MASX J20162627+5017501
2019-04-27 10:52  303.8571  +60.4465  2MASX J20152569+6026477
2019-04-27 10:55  303.3392  +63.0623  2MASX J20132145+6303444
2019-04-27 10:59  304.6876  +54.4322  2MASX J20184502+5425559
2019-04-27 11:02  353.4731  +80.9441  2MFGC 17682
2019-04-27 11:05  304.5325  +50.8713  2MASX J20180778+5052164
2019-04-27 11:12  302.3811  +48.1482  2MASX J20093146+4808535
2019-04-27 11:16  315.4480  +57.7256  2MASX J21014752+5743323
2019-04-27 11:19  306.0262  +68.2791  2MASX J20240632+6816442
2019-04-27 11:23  304.6915  +54.4077  UGC 11538
2019-04-27 11:26  302.9347  +62.4006  2MASX J20114430+6224020
2019-04-27 11:29  316.2281  +65.7095  2MASX J21045475+6542340
2019-04-27 11:33  305.4544  +44.0110  2MASX J20214907+4400399
2019-04-27 11:36  015.3454  +82.0982  2MASX J01012279+8205535
2019-04-27 11:40  324.9967  +78.4497  2MASX J21395910+7826585
2019-04-27 11:46  292.9330  +02.7058  2MASX J19314391+0242209

Niino, Y., Morokuma, T., Ohsawa, R., Sako, S., Shikauchi, M. (U. of Tokyo), 
Yanagisawa, K. (NAOJ), 
Takagi K., Nakaoka, T., Sasada, M.(Hiroshima U.),
Saito, T. (Nishi-Harima Astronomical observatory), 
Itoh, R. (Bisei Astronomical Observatory), 
Ohta, K. (Kyoto U.), 
Utsumi, Y. (Stanford U./SLAC), 
Sekiguchi, Y. (Toho U.), 
Tominaga, N. (Konan U.), 
on behalf of J-GEM collaboration

We report our optical and near-infrared imaging observations for the gravitational wave event S190426c that has a non-zero probability to be a NS-BH merger. 

We performed 180 deg2 wide-field imaging survey, using the Tomo-e Gozen camera on the 105-cm Kiso Schmidt telescope, a very wide-field (20 deg2 field-of-view) optical CMOS imager (Sako et al. 2018, SPIE, 10702, 107020J). The observations started about 19 hours after the GW detection. A typical limiting magnitude is about 20 mag (no filter). Data reduction is in progress. 

We also performed galaxy-targeted observations for 33 galaxies (see the table below) selected from the GLADE catalog (Dalya et al. 2016) in the probability skymap of S190426c using the following telescopes/instruments.
- 91 cm Okayama Astrophysical Observatory NIR Wide���Field Camera 
  (OAOWFC, J-band, Yanagisawa, K., et al. 2014, Proc. SPIE, 9147, 91476D, 
  Yanagisawa, K., et al. 2016, Proc. SPIE, 9908, 99085D)
- 150 cm Kanata telescope at Higashi-Hiroshima Observatory and HONIR, a 2 color imager in Rc and H bands (Akitaya et al. 2014, 9147, 91474O)
- 200 cm Nayuta telescope at Nishi-Harima Astronomical Observatory 
  and Nishiharima Infrared Camera (NIC)

We found no apparent transient objects in these galaxies 
to the 5 sigma limiting magnitudes listed below.


         galid   ra dec    J H R NoFilt      K obsid
GL204400+531432  310.9979 53.2423  17.08 -- --      -- -- OAOWFC
GL221519+843451  333.8273 84.581     -- -- -- 99.99     -- Kiso Schmidt
GL232822+852913  352.0922 85.4869     -- 99.99 99.99 --     -- Kanata-HONIR
GL233253+853017   353.222 85.5048   -- 15.35 17.65 --     -- Kanata-HONIR
GL002228+854955     5.617 85.8321 17.33  17.24 -- -- 99.99        Nayuta
GL011607+845904   19.0275 84.9843   -- -- -- --  99.99 Nayuta
GL235357+842524  358.4862 84.4233     -- -- -- 99.99    -- Kiso Schmidt
GL233600+852510  353.9992 85.4196     -- -- 17.65 --     -- Kanata-HONIR
GL235923+834710  359.8466 83.7861     -- 99.99 -- --     -- Kanata-HONIR
GL223741+844405  339.4209 84.7347     -- -- -- 99.99    -- Kiso Schmidt
GL215853+832141  329.7229 83.3614     -- -- -- 99.99    -- Kiso Schmidt
GL214359+841507  325.9938 84.2519     -- -- -- 18.29     -- Kiso Schmidt
GL222416+864727  336.0676 86.7909     -- -- -- 99.99     -- Kiso Schmidt
GL205538+853151  313.9084 85.5307     -- -- -- 99.99     -- Kiso Schmidt
GL233600+852604  353.9975 85.4346     -- 15.35 17.65 --     -- Kanata-HONIR
GL201328+463031  303.3651 46.5087  17.57 -- --      -- -- OAOWFC
GL221751+832357  334.4629 83.3993     -- -- -- 99.99     -- Kiso Schmidt
GL205927+845437  314.8623 84.9103     -- -- -- 99.99     -- Kiso Schmidt
GL224440+824209  341.1686 82.7026     -- -- -- 18.95     -- Kiso Schmidt
GL225030+824531  342.6235 82.7586     -- -- -- 19.00     -- Kiso Schmidt
GL201355+462212  303.4775 46.3701  17.57 -- --      -- -- OAOWFC
GL235428+842518  358.6179 84.4217     -- -- -- 99.99    -- Kiso Schmidt
GL223827+872835  339.6125 87.4764     -- -- -- 17.11     -- Kiso Schmidt
GL180154+865139  270.4751 86.8608     -- -- -- 17.75     -- Kiso Schmidt
GL233512+852612  353.7982 85.4366     -- 15.35 17.65 --     -- Kanata-HONIR
GL215728+854334  329.3673 85.7262     -- -- -- 15.99     -- Kiso Schmidt
GL194045+874800   295.188 87.7998   -- -- -- 17.69     -- Kiso Schmidt
GL150924+865350  227.3519 86.8972     -- -- -- 99.99     -- Kiso Schmidt
GL211419+871821  318.5808 87.3058     -- -- -- 17.59     -- Kiso Schmidt
GL204129+862633  310.3714 86.4425     -- -- -- 99.99     -- Kiso Schmidt
GL233452+852734  353.7174 85.4593     -- 15.35 17.65 --     -- Kanata-HONIR
GL173106+875633  262.7764 87.9426     -- -- -- 18.29     -- Kiso Schmidt
GL212800+853445  321.9959 85.5793     -- -- -- 18.29     -- Kiso Schmidt

Note that a limiting mag = 99.99 is due to failure in our real-time data analysis.

Eleonora Troja (GSFC/UMD), Rosa L. Becerra (UNAM), Nat Butler (ASU), 
Alan M. Watson (UNAM), Simone Dichiara (UMD), Diego Gonz��lez (UNAM),
Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Margarita Pereyra
(UNAM), and Tanner Wolfram (ASU) report:

We observed 22 galaxies selected from the NED/CLU list for LIGO/Virgo
S190426c (Chatterjee et al, GCN Circ. 24237
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 ) with the Reionization and
Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold
Johnson Telescope at the Observatorio Astron��mico Nacional on Sierra San
Pedro M��rtir on the night of 2019-04-27 UTC. For each galaxy, we
typically obtained 720 seconds of exposure in g and i filters and 540
seconds of exposure in Y and H filters. Typical 10-sigma limiting
magnitudes are i = 21.2. Our observations are listed below. Visual
inspection reveals no obvious counterpart candidates.

We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.

Start (UTC)       RA and Dec (J2000)  Galaxy
2019-04-27 03:30  166.8817  +00.7831  IC 0671
2019-04-27 04:10  167.0731  -05.1323  MCG -01-29-002
2019-04-27 04:27  169.4779  -01.9464  IC 0680
2019-04-27 04:43  166.6895  -04.0722  2MASX J11064547-0404202
2019-04-27 05:10  166.3304  -03.9763  LCRS B110246.5-034222
2019-04-27 05:26  168.2716  +00.0030  2MASX J11130517+0000108
2019-04-27 05:43  170.8150  -05.5724  LCRS B112043.2-051740
2019-04-27 06:01  170.1643  -05.6714  MCG -01-29-010 NED01
2019-04-27 06:27  170.7156  -02.9109  CGCG 011-082
2019-04-27 07:19  168.0636  -05.7535  MCG -01-29-005
2019-04-27 07:50  169.4203  -04.4609  2MFGC 08820
2019-04-27 08:09  163.6089  +07.1427  CGCG 038-046
2019-04-27 08:27  300.5817  +43.1268  2MASX J20021959+4307366
2019-04-27 08:45  308.2331  +54.5088  UGC 11592
2019-04-27 09:12  311.7825  +57.5936  4C +57.35
2019-04-27 09:31  305.9863  +25.7011  2MASX J20235668+2542038
2019-04-27 09:52  302.6869  +17.7386  2MASX J20104485+1744189
2019-04-27 10:24  305.5413  +24.9932  2MASX J20220989+2459351
2019-04-27 10:42  300.6474  +14.9513  2MASX J20023539+1457045
2019-04-27 11:00  301.1253  +19.4085  2MASX J20043008+1924304
2019-04-27 11:16  299.3077  +19.0874  2MASX J19571383+1905142
2019-04-27 11:41  289.0384  -00.7858  2MFGC 14839

-- 
Dr. Alan M. Watson
Instituto de Astronom��a
Universidad Nacional Aut��noma de M��xico

Alan M. Watson (UNAM), Nat Butler (ASU), Eleonora Troja (GSFC/UMD), Rosa
L. Becerra (UNAM), Simone Dichiara (UMD), Diego Gonz��lez (UNAM),
Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Margarita Pereyra
(UNAM), and Tanner Wolfram (ASU) report:

We observed 8 fields of LIGO/Virgo S190426c (Chatterjee et al, GCN Circ.
24237
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 ) with the DDOTI/OAN wide-field imager at the Observatorio
Astron��mico Nacional on Sierra San Pedro M��rtir
(http://ddoti.astroscu.unam.mx) on the night of 2019-04-27 UTC. Some
fields were visited more than once. Each visit consisted of 1080 seconds
in the w filter. Our observations are listed below. Analysis is
proceeding.

Due to hardware problems (a failed CCD power supply and a jammed
focuser), we only observed with only four of the six telescopes and
obtained about 48 square degrees at each visit rather than the full 72
square degrees.

We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.

Start (UTC)       RA and Dec (J2000)
2019-04-27 06:03  21:40:22.6 +85:17:25
2019-04-27 06:33  21:40:22.6 +85:17:25
2019-04-27 07:00  21:40:22.6 +85:17:25
2019-04-27 07:26  20:50:51.8 +63:40:00
2019-04-27 07:53  20:50:51.8 +63:40:00
2019-04-27 08:20  20:25:31.7 +47:46:54
2019-04-27 08:47  20:16:56.0 +39:52:13
2019-04-27 09:13  20:36:33.3 +56:11:28
2019-04-27 09:40  19:59:21.3 +24:29:14
2019-04-27 10:07  20:05:19.9 +31:51:18
2019-04-27 10:34  21:40:22.6 +85:17:25
2019-04-27 11:01  23:55:06.2 +83:59:48

G. Waratkar, H. Kumar, V. Bhalerao, V. Karambelkar (IITB), G. C. Anupama,
J. Stanzin (IIA) report on behalf of the GROWTH collaboration:

We followed up the localization region of the GW candidate event S190426c
(LVC et al. GCN 24168
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 ) with the GROWTH-India telescope. We obtained 37
r-band overlapping images covering a total area of 12.3 square degrees,
with 9.43% probability of containing the GW counterpart. Exposures were 600
seconds long and reached a typical depth of 20.6 magnitude. The field
centers (given below) were chosen in coordination with ZTF and DECAM (GCN
24257
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 ) to cover the northernmost part of the sky not accessible to them.
Data processing is underway. These fields contain 332 galaxies from the
GLADE catalog and 6 galaxies from NED. We inspected the NED galaxies
(listed below) and do not find any candidate counterparts near them.

List of NED galaxies:
Name, RA, Dec
2MASX J22163720+8655469, 334.156, 86.929
VII Zw 938, 314.169, 87.880
HDCE 1209, 342.180, 86.83
UGC 12387, 346.084, 86.749
UGC 12377, 345.857, 86.766
CGCG 360-004, 18.977, 85.165

List of observed fields:
    RA        Dec
315.000 87.441
003.214 84.882
012.273 85.979
018.750 85.613
009.000 84.516
010.385 85.247
003.462 85.247
343.125 87.076
004.091 85.979
016.071 84.882
337.500 87.807
322.500 87.807
354.375 87.076
355.500 86.345
353.571 87.441
005.625 87.076
356.538 85.247
335.000 86.710
331.875 87.076
015.000 84.516
340.714 87.441
325.000 86.710
355.000 86.710
009.643 84.882
013.500 86.345
017.308 85.247
003.750 85.613
327.857 87.441
005.000 86.710
352.500 87.807
345.000 86.710
008.438 84.150
356.250 85.613
320.625 87.076
004.500 86.345
011.250 85.613
328.500 86.345

The GROWTH India Telescope (GIT) is a 70-cm telescope with a 0.7 degree
field of view, set up by the Indian Institute of Astrophysics and the
Indian Institute of Technology Bombay with support from the Indo-US Science
and Technology Forum (IUSSTF) and the Science and Engineering Research
Board (SERB) of the Department of Science and Technology (DST), Government
of India (https://sites.google.com/view/growthindia/). It is located at the
Indian Astronomical Observatory (Hanle), operated by the Indian Institute
of Astrophysics (IIA).

A. F. Valeev and V. V. Sokolov (SAO-RAS), A. J. Castro-Tirado, Y.-D. Hu, 
X.-Y. Li, A. Ayala, E. Fernandez-Garcia and F. J. Aceituno (IAA-CSIC), 
I. Carrasco, A. Castellon and C. Perez del Pulgar (UMA), M. D. 
Caballero-Garcia (ASU-CAS), S. B. Pandey (ARIES) and N. Castro-Rodriguez 
(GRANTECAN, IAC, ULL), on behalf of a larger collaboration, report:

Following the detection of the two new transients DG19ytre and DG19kplb 
(Andreoni et al., GCN 24268
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 ) within the error area of the GW event 
S190426c (LIGO Scientific Collaboration and the Virgo Collaboration, GCN 
24237
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 ), we observed the two targets with the 1.5m telescope at the 
Observatorio de Sierra Nevada (Spain) in the BVRI-bands, starting on Apr 
27, 20:53 UT. In addition, optical spectra for each target (1200s) 
covering the range 3700-7500 A were obtained with the 10.4m GTC  
telescope equipped with OSIRIS in La Palma (Spain) starting on Apr 27, 
21:40 UT.

DG19kplb is found to be in the outskirts of its host galaxy at a 
redshift z = 0.09123. The spectrum resembles that of a broad-line Type 
Ic SN at the same redshift past maximum.

DG19ytre is north of a galaxy at redshift z = 0.1825 and displays Type 
Ia SN features consistent with z = 0.1386.

Therefore none of these two newly reported transients seem to be related 
to the GW event S190426c.

We acknowledge the excellent support from the GTC staff.

Gregory S.H. Paek (SNU), Myungshin Im (SNU), Hyun-Il Sung (KASI), Gu Lim
(SNU), Joonho Kim (SNU), Sungyong Hwang (SNU), Bomi Park (SNU), Sophia Kim
(SNU), Changsu Choi (SNU), Chung-Uk Lee (KASI), Seung-Lee Kim (KASI), Hyung
Mok Lee (KASI), on behalf of a larger collaboration

We observed 23 host galaxy candidates with the 1.0-m telescope at the
Lemonsan Optical Astronomical Observatory(LOAO) in the 90% updated
localization area of S190426c, detected by LIGO/Virgo (GCN #24237
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 ).
The observation started at 2019-04-27 09:14:26, and the images were taken
twice in R-band with 120 sec exposure time. No obvious transient has been
identified to a preliminary 3-sigma depth of R=20.8 AB mag. The list of the
inspected targets is given below.

NAME                    RA            DEC
2MASS+20300804+5415120    307.533508    54.253361
2MASS+20232657+5347113    305.860718    53.786499
2MASS+20175967+5440389    304.498657    54.677479
2MASS+20292607+5411091    307.358643    54.185883
2MASS+20205571+5530336    305.232147    55.509338
2MASS+20355212+5549587    308.967194    55.832996
2MASS+20305041+5537391    307.710052    55.627537
2MASS+20183442+5619548    304.643433    56.331894
2MASS+20360197+5350457    309.008209    53.846035
2MASS+20363163+5824495    309.131805    58.41375
2MASS+20403391+5348447    310.141296    53.812439
2MASS+20262902+5827565    306.620941    58.465717
2MASS+20290191+5817016    307.257996    58.283779
2MASS+20243518+5606523    306.146606    56.114536
2MASS+20235181+6448514    305.965881    64.814285
2MASS+20431631+6211283    310.817993    62.1912
2MASS+21072317+6322504    316.846558    63.38068
2MASS+20323093+6451261    308.128906    64.857254
2MASS+20391049+6303489    309.793732    63.063591
2MASS+20563318+6814486    314.138275    68.246841
2MASS+20453544+6259029    311.397705    62.984146
2MASS+21011016+6334464    315.292358    63.579582
2MASS+20550853+6249236    313.785583    62.823235

The observation of host galaxy candidates and the analysis of the data are
ongoing.
We thank the LOAO opertator for performing the observation.

B. J. Shappee (IfA-Hawaii), C. S. Kochanek (OSU), K. Z. Stanek (OSU), S.
Holmbo (Aarhus), A. Franckowiak (DESY), T. W.-S. Holoien (Carnegie
Observatories), J. L. Prieto (Diego Portales; MAS), Subo Dong (KIAA-PKU),
 T. A. Thompson (OSU), J. F. Beacom (OSU)

Following the LIGO/VIRGO alert of gravitational wave source S190426c (GCN #
24237), optical follow-up was triggered with the All-Sky Automated Survey
for SuperNovae (ASAS-SN, Shappee et al. 2014; Kochanek et al. 2017).   ASAS-SN
covered 77% of the updated probability region (GCN #24277
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 , 24279
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 ) in the 24
hours after the LIGO/VIRGO alert through a combination of normal operations
and triggered observations.  We note that we covered 86% of the
preliminary localization
region.  We obtained up to 13 epochs on the highest probability regions
during that time. Candidates were scanned in near real time. No obvious
candidates were discovered. Given the lunation, our depth was typically
between g~18-18.5 mag.

Our coverage is shown here:

http://www.astronomy.ohio-state.edu/~assassin/LIGO/S190426c_coverage.png

Our coverage compared to the preliminary localization region is shown here:

http://www.astronomy.ohio-state.edu/~assassin/LIGO/S190426c_prelim_coverage.png

We would like to thank Las Cumbres Observatory and its staff for their
continued support of ASAS-SN. ASAS-SN is funded in part by the Gordon and
Betty Moore Foundation through grant GBMF5490 to the Ohio State University,
NSF grant AST-1515927, the Mt. Cuba Astronomical Foundation, the Center for
Cosmology and AstroParticle Physics (CCAPP) at OSU, the Chinese Academy of
Sciences South America Center for Astronomy (CASSACA), and the Villum
Fonden (Denmark). For more information about the ASAS-SN project, see
http://www.astronomy.ohio-state.edu/asassn/index.shtml.

M. Blazek (HETH/IAA-CSIC), D. Corre (LAL), E. Howell (OzGrav-UWA),
N. Christensen (Artemis), M. Vardosanidze (Iliauni), D. A. Kann
(HETH/IAA-CSIC), K. Bensch (HETH/IAA-CSIC), L. Izzo (HETH/IAA-CSIC),
C. Thoene (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC,
DARK/NBI), S. Antier (APC), S. Basa (LAM), M. Boer (Artemis),
M. Coughlin (Caltech), D. Coward (OzGrav-UWA), J.G. Ducoin (LAL),
B. Gendre (OzGrav-UWA), P. Hello (LAL), A. Klotz (IRAP),
C. Lachaud (APC), N. Leroy (LAL), D. Turpin (NAOC), X. Wang (THU),
and X. Zhang (THU)

report on behalf of the HETH group and GRANDMA collaboration.

We performed observations of LIGO/Virgo event S190426c (GCN #24237
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 ) with
the OAJ-T80 telescope operating in the visible located at Javalambre
astronomical observatory (Teruel, Spain).

The observation started on 04/26/19 21:40:23 UTC which corresponds
approximately to 6.3 hours after the GW trigger time.

We performed the following observations in r band:

+------------+------------+---------+---------+---------+
| Tstart     | Tend       | RA      | DEC     |   Proba |
| [UTC]      | [UTC]      | [deg]   | [deg]   |     [%] |
|------------+------------+---------+---------+---------|
| 2019-04-26 | 2019-04-26 | 0.000   | 84.000  |     1.0 |
| 21:40:23   | 21:43:24   |         |         |         |
| 2019-04-26 | 2019-04-26 | 340.000 | 84.000  |     0.7 |
| 21:43:52   | 21:46:52   |         |         |         |
| 2019-04-26 | 2019-04-26 | 330.000 | 86.000  |     0.9 |
| 21:50:01   | 21:53:01   |         |         |         |
| 2019-04-26 | 2019-04-26 | 0.000   | 82.000  |     0.4 |
| 21:53:32   | 21:56:32   |         |         |         |
| 2019-04-26 | 2019-04-26 | 0.000   | 86.000  |     0.8 |
| 21:56:59   | 22:00:00   |         |         |         |
| 2019-04-27 | 2019-04-27 | 309.600 | 56.000  |     0.5 |
| 01:20:38   | 01:23:38   |         |         |         |
| 2019-04-27 | 2019-04-27 | 305.280 | 46.000  |     0.5 |
| 01:28:57   | 01:31:58   |         |         |         |
| 2019-04-27 | 2019-04-27 | 301.935 | 30.000  |     0.4 |
| 01:34:18   | 01:37:19   |         |         |         |
| 2019-04-27 | 2019-04-27 | 300.760 | 28.000  |     0.4 |
| 01:37:46   | 01:40:46   |         |         |         |
| 2019-04-27 | 2019-04-27 | 306.000 | 48.000  |     0.4 |
| 01:41:17   | 01:44:18   |         |         |         |
| 2019-04-27 | 2019-04-27 | 313.846 | 64.000  |     0.5 |
| 01:47:29   | 01:50:29   |         |         |         |
| 2019-04-27 | 2019-04-27 | 309.231 | 64.000  |     0.4 |
| 01:50:56   | 01:53:57   |         |         |         |
| 2019-04-27 | 2019-04-27 | 299.627 | 26.000  |     0.4 |
| 01:54:34   | 01:57:35   |         |         |         |
| 2019-04-27 | 2019-04-27 | 300.789 | 32.000  |     0.4 |
| 01:58:03   | 02:01:04   |         |         |         |
| 2019-04-27 | 2019-04-27 | 304.186 | 44.000  |     0.4 |
| 02:01:33   | 02:04:33   |         |         |         |
| 2019-04-27 | 2019-04-27 | 302.013 | 34.000  |     0.4 |
| 02:07:46   | 02:10:47   |         |         |         |
| 2019-04-27 | 2019-04-27 | 306.783 | 50.000  |     0.4 |
| 02:11:16   | 02:14:16   |         |         |         |
| 2019-04-27 | 2019-04-27 | 310.737 | 58.000  |     0.4 |
| 02:14:48   | 02:17:48   |         |         |         |
| 2019-04-27 | 2019-04-27 | 302.897 | 36.000  |     0.4 |
| 02:18:22   | 02:21:22   |         |         |         |
| 2019-04-27 | 2019-04-27 | 303.830 | 38.000  |     0.4 |
| 02:25:13   | 02:28:14   |         |         |         |
| 2019-04-27 | 2019-04-27 | 298.537 | 24.000  |     0.4 |
| 02:28:43   | 02:31:43   |         |         |         |
| 2019-04-27 | 2019-04-27 | 308.571 | 54.000  |     0.4 |
| 02:32:20   | 02:35:20   |         |         |         |
+------------+------------+---------+---------+---------+

The probability refers to the 2D spatial probability of the GW (initial)
skymap enclosed in a given tile. Each tile is 1.4x1.4 degrees. These
observations cover about 11% of the cumulative probability of the skymap.
The typical limiting magnitude is 19.6 for a 180 s exposure.

The coverage map is available at:
https://grandma-owncloud.lal.in2p3.fr/index.php/s/jWlewyAy823F2sZ

No transients related to the GW event have been found when comparing sky
regions around GLADE galaxies with PS1 template observations.

GRANDMA (Global Rapid Advanced Network Devoted to the Multi-messenger
Addicts) is a network of robotic telescopes connected all over the world
with both photometry and spectrometry capabilities for Time-domain
Astronomy (https://grandma.lal.in2p3.fr/).

HETH (High Energy Transients and Their Hosts) is funded by Spanish
National Research Grant of Excellence, Ramon y Cajal fellowships and
research funding, Juan de la Cierva Incorporation fellowships and
research funding (http://heth.iaa.es/).

Details on the OAJ-T80 telescope are available at http://oajweb.cefca.es

This circular is citable.

M. Hankins (Caltech), K. De (Caltech), M. Coughlin (Caltech), M. M.

Kasliwal (Caltech), S. M. Adams (Caltech), I. Andreoni (Caltech), S.

Anand (Caltech), L. Singer (NASA GSFC), T. Ahumada (UMD),  A. Moore

(ANU), J. Soon (ANU), M. Ashley (UNSW), T. Travouillon (ANU), R. Lau (ISAS JAXA)


report on behalf of the Palomar Gattini-IR team and the larger GROWTH

(Global Relay of Observatories Watching Transients Happen)

collaboration


We report continuing wide-field near-infrared follow-up observations (GCN #24284
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 )

of the localization region of the gravitational wave event S190426c (GCN

#24237
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 ) by the Palomar Gattini-IR survey (Moore and Kasliwal 2019).

Gattini-IR is a newly commissioned near-IR camera with a field of view

of 25 square degrees mounted on a robotic 30 cm telescope at Palomar

observatory.


We started customized Target of Opportunity observations at UT

2019-04-28 03:28. The tiling was optimally determined and triggered

using the GROWTH Target of Opportunity marshal (Coughlin et al. 2019a,

Kasliwal et al. 2019b). We imaged a total of 1900 square degrees,

covering 94% of the probability region of the event for 1 to 5 epochs

until UT 2019-04-28 12:33. Each field visit consisted of a sequence of

8 dithers of 8 second exposures each on the field, which were

processed and stacked with the Palomar Gattini-IR data reduction

pipeline (De et al., in prep.). The typical limiting magnitude of each

stacked epoch (64 second exposure time) was between 14.5 and 15.5 AB mag

in J-band, and shallower than usual due to poor weather conditions.

No viable counterparts without previous history of variability were identified.

Daniel A. Perley (LJMU), Ariel Goobar (OKC), Mansi M. Kasliwal 
(Caltech), Michael W. Coughlin (Caltech), Adam A. Miller (Northwestern), 
Tomas Ahumada (UMD), Jacob Jencson (Caltech), Harsh Kumar (IITB), David 
Kaplan (UWM), Shreya Anand (Caltech),  Leo P. Singer (NASA GSFC), Igor 
Andreoni (Caltech), Varun Bhalerao (IITB), Danny Goldstein (Caltech), 
Dmitry Duev (Caltech), S. Bradley Cenko (NASA GSFC),  Eric C. Bellm 
(UW), Kishalay De (Caltech),  Rahul Biswas (OKC), Kishalay De (Caltech), 
and Joshua Bloom (UCB) report on behalf of the Zwicky Transient Facility 
(ZTF) and Global Relay of Observatories Watching Transients Happen 
(GROWTH) collaborations:

We continued observations of the gravitational wave trigger S190426c 
(LVC et al. GCN 24237
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 ) with ZTF on UT 2019-04-28. We covered 1150 sq deg 
in g-band and r-band with over 54% of the enclosed probability targeted 
based on the latest sky map (LALInference1.fits.gz, GCN 24277
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 ). Each 
exposure on the second night was 300s, with a typical depth of 22 mag. 
In total, over both nights, we have covered 4420 sq deg, enclosing 56% 
of the the total probability. See details in Coughlin et al. (GCN 24283
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 ) 
for additional details on data processing.

Additional candidates with no detections prior to merger, inside the 90% 
localization area of the LALInference sky map, and not consistent with 
the locations of known AGN or other variable objects, are:

------------------------------------------------------------------------------------------------
ZTF Name     | RA (deg)    | DEC (deg)  | Filt.| Mag.  | Magerr | Notes
------------------------------------------------------------------------------------------------
ZTF19aasmftm | 325.9004479 | 77.8315634 |    g | 21.16 | 0.12   | [rising]
ZTF19aaslvwn | 299.059846  | 46.463559  |    g | 20.83 | 0.12   | [lowb]
ZTF19aasmdir | 300.2360007 |  9.504002  |    g | 20.35 | 0.09   | [lowb] 
[nuc] [agn?]
ZTF19aaslzjf | 320.6262982 | 65.8134516 |    r | 20.54 | 0.09   | [lowb]
ZTF19aassfws | 298.6678611 | 61.2400121 |    r | 21.41 | 0.20   | 
photz~0.07 +/- 0.03 [nuc]
ZTF19aasmddt | 299.25055   |  9.7016748 |    g | 20.00 | 0.08   | 
photz~0.08 +/- 0.04 [lowb]
ZTF19aaslszp | 301.3434628 | 53.3990477 |    g | 20.84 | 0.11   | 
photz~0.062 [lowb] [nuc?]
ZTF19aasmekb | 300.6013987 | 14.2873159 |    g | 18.29 | 0.03   | [lowb] 
[hostless] [fading]
ZTF19aaslolf | 288.7838539 | 79.4357187 |    g | 21.33 | 0.19   | 
photz~0.42+/-0.20 [nuc] [agn?]
ZTF19aaslphi | 297.3809977 | 61.9605925 |    g | 21.24 | 0.17   | 
photz~0.16+/-0.02
ZTF19aaslpds | 306.2625186 |  61.521461 |    r | 20.99 | 0.13   | [lowb]
ZTF19aaslozu | 306.3144981 | 65.1093759 |    r | 20.87 | 0.16   |
ZTF19aasshpf | 315.4768651 | 70.2055771 |    r | 21.42 | 0.18   |
ZTF19aasmzee | 296.8366485 |  5.1534971 |    r | 20.33 | 0.09   | [lowb]
ZTF19aasmzqf | 353.5204911 | 78.9577781 |    g | 20.53 | 0.09   |
----------------------------------------------------------------------------------------------
Notes:
[rising] : Rising light curve
[lowb] : Galactic latitude less than 15 degrees
[agn?] : WISE colors consistent within an AGN within 1" of the transient.
[hostless] : No discernable host galaxy or other counterpart.
[nuc] : Close to the host nucleus.
[fading] : Clear fading is observed over the past two nights, with no 
prior rise.  This may indicate a CV / dwarf nova.

Three candidates (ZTF19aassfws, ZTF19aasmddt, ZTF19aaslszp) are 
interesting given that their photometric redshifts are consistent with 
the LVC error volume.  ZTF19aaslzjf is also in a galaxy that is likely 
nearby, although no redshift estimate is available.  ZTF19aasmftm is 
interesting given a (probable) rising light curve that suggests a young 
object, although its galaxy counterpart is very faint (r=21.2 in PS1). 
Deep upper limits preceding the detections are not available for any of 
these sources, and they could be unrelated SNe.

Additional follow-up and analysis is ongoing.

ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; 
IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; 
DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, 
Japan; IIT-B, India; IIA, India; LJMU, UK; TTU USA and USyd, Australia. 
ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 
1440341. GROWTH acknowledges generous support of the NSF under PIRE 
Grant No 1545949. Alert distribution service provided by DIRAC@UW 
(Patterson et al. 2019). Alert filtering and follow-up co-ordination is 
being undertaken by the GROWTH marshal system (Kasliwal et al. 2019).













DisclaimerNone

Gregory S.H. Paek (SNU), Myungshin Im (SNU), Hyun-Il Sung (KASI), Gu Lim
(SNU), Joonho Kim (SNU), Sungyong Hwang (SNU), Bomi Park (SNU), Sophia Kim
(SNU), Changsu Choi (SNU), Chung-Uk Lee (KASI), Seung-Lee Kim (KASI), Hyung
Mok Lee (KASI), on behalf of a larger collaboration

We observed 17 host galaxy candidates with the 1.0-m telescope at the
Lemonsan Optical Astronomical Observatory(LOAO) in the 90% updated
localization area of S190426c, detected by LIGO/Virgo (GCN #24237
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 ).
The observation started at 2019-04-28 09:59:34.500, and the images were
taken twice in R-band with 120 sec exposure time. No obvious transient has
been identified to a preliminary 3-sigma depth of R=19.6 AB mag. The list
of the inspected targets is given below.

NAME                    RA            DEC
2MASS+00320124+8337292  00:32:01.200 +83:37:29.30
2MASS+00431317+8418363  00:43:13.200 +84:18:36.30
2MASS+00432208+8527102  00:43:22.100 +85:27:10.30
2MASS+00450100+8538272  00:45:01.000 +85:38:27.20
2MASS+00533469+8539080  00:53:34.700 +85:39:08.10
2MASS+00592185+8521346  00:59:21.900 +85:21:34.70
2MASS+01042304+8335416  01:04:23.000 +83:35:41.70
2MASS+01051541+8511586  01:05:15.400 +85:11:58.60
2MASS+01065962+8521066  01:06:59.600 +85:21:06.70
2MASS+01073984+8711285  01:07:39.800 +87:11:28.60
2MASS+01125057+8546555  01:12:50.600 +85:46:55.60
2MASS+01160660+8459035  01:16:06.600 +84:59:03.50
2MASS+01190649+8504131  01:19:06.500 +85:04:13.20
2MASS+01264881+8506094  01:26:48.800 +85:06:09.50
2MASS+01333891+8532521  01:33:38.900 +85:32:52.20
PGC3005                 00:52:03.700 +85:23:32.60
PGC3085929              00:41:52.300 +84:22:56.10

We thank the LOAO opertator for performing the observation.

L. Izzo (IAA), R. Carini (INAF-OAR), S. Yang (INAF-OAPd), L. Tomasella (INAF-OAPd), E. Cappellaro (INAF-OAPd), G. Greco (Univ. Urbino), R. Martone (U. Ferrara), S. Benetti (INAF-OAPd), M.T. Botticella (INAF-OAC), M. Branchesi (GSSI), S. Campana (INAF-OAB), S. Covino (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASI-SSDC), M. Della Valle (INAF-OAC), A. Melandri  (INAF-OAB), S. Piranomonte (INAF-OAR), A. Rossi (INAF-OAS), E. Brocato (INAF-OAAb, INAF-OAR), on behalf of GRAWITA report:

We carried out observations of LIGO/Virgo S190426c (LVC, GCN Circ. 24237
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 ) with the Schmidt Telescope located at the INAF Asiago Observatory (Italy). The observations were taken in the r-sloan band on 2019-04-26 starting on 22:16:27 UT. Each pointing covers an area of 1x1 deg and each exposure was of 90 s. The covered area captured a contained probability of ~1.6% of the GW skymap (LALInference1, submitted by LIGO/Virgo EM Follow-Up on Apr 27, 2019 11:50:29 UTC).

The pointings are centered on the following UT times and coordinates RA(J2000), Dec(J2000):

2019-04-26T22:27:23  22:19:19.87  +82:59:58
2019-04-26T22:32:38  22:19:20.51  +84:59:59
2019-04-26T22:37:08  21:59:57.43  +83:00:00
2019-04-26T22:40:52  22:00:00.31  +84:00:00
2019-04-26T22:44:49  21:59:59.51  +84:59:59

A preliminary analysis of the dataset reveals the presence of the following transient sources (ID, RA(J2000, Dec(J2000), r(AB) mag, probability by LALInference1 skymap): 

GRAWITA_J215716.26+832239.4    21:57:16.26    +83:22:39.4  15.1   within 30% c.r.   
GRAWITA_J220104.54+834836.9    22:01:04.54    +83:48:36.9  16.9   within 30% c.r.  
GRAWITA_J220050.38+844436.5    22:00:50.38    +84:44:36.5  16.7   within 20% c.r.    

There are no known source at the position of these sources and no minor planets. Inspection of archival Pan-STARRS images reveals no objects at the position of GRAWITA_J215716.26+832239.4 and GRAWITA_J220104.54+834836.9, while a faint source can be recognised at the position of GRAWITA_J220050.38+844436.5.

Subsequently, we carried out follow-up observations, starting at 22:58:43 UT on 2019-04-28, with the 0.5m telescope of the Osservatorio Astronomico S. Di Giacomo located in Agerola, Italy (https://goo.gl/Dqvqhf) of GRAWITA_J220104.54+834836.9 and GRAWITA_J220050.38+844436.5. Both sources are no longer detected down to a 3sigma limiting magnitude of R(AB)>19.4.

Further analysis is in progress.

V. Lipunov, N.Tyurina, E. Gorbovskoy, V.Kornilov, D.Vlasenko, V.Vladimirov, D.Zimnukhov, A.Kuznetsov,
P.Balanutsa, I.Gorbunov, A. Chasovnikov, V.Grinshpun, F.Balakin, T.Pogrosheva (Lomonosov Moscow State University, SAI, Physics Department),

R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres (The Instituto de Astrofisica de Canarias),

R. Podesta, C. Lopez, C.Francile, F. Podesta (Observatorio Astronomico  Felix Aguilar OAFA, San Juan National University),

H.Levato (Instituto de Ciencias Astronomicas, de la Tierra y del Espacio ICATE,SJNU)

D. Buckley (South African Astronomical Observatory),

O. Gress, N.M. Budnev, O.Ershova (Applied Physics Institute, Irkutsk Stat University),

V. Yurkov, A. Gabovich, Yu. Sergienko, D. Kobcev (Blagoveschensk EducationState University),

A. Tlatov, V.Senik, A.V. Parhomenko, D. Dormidontov (Kislovodsk Solar  Station of the Pulkovo Observatory),

MASTER Global Robotic Net (http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)
started inspect of GW190426 /  LIGO/Virgo S190426c errorbox (Chatterjee et al. GCN 24237
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  https://gcn.gsfc.nasa.gov/other/S190426c.gcn3 )
at 2019-04-26 16:15:47 UT  (Lipunov et al. GCN 24236
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 ) and continuied  several nights.

There is no OTs at GRAWITA positions ( Izzo et al. GCN 24340
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  ) several hours befor

1) 21 57 16.26 +83 22 39.4
Date_UT             unfiltmlim    MASTER_observatory
2019-04-26 20:38:02      19.6     MASTER-Kislovodsk
2019-04-26 18:38:53      19.6     MASTER-Tavrida
2019-04-26 16:41:15      19.2	  MASTER-Tunka

There is variable star in 5", presented in GSC2.3.2 (red fmag=19.9 in 1996), PanSTARR source with rmag=20.73(2010Dec30). It's not presented in 
USNO-B1, it means 22mPOSS limit in history.

2)  22:01:04.54    +83:48:36.9
Date_UT            unfiltmlim   MASTER_observatory
2019-04-26 20:38:02    19.6    MASTER-Kislovodsk
2019-04-26 18:38:53    19.6    MASTER-Tavrida
2019-04-26 16:25:18    19.6    MASTER-Tunka
2019-04-27 11:59:22    16.5    MASTER-Amur

there is also a star in 6.9" in PanSTARR catalogue with imag=21.14 (no  g,r)

3) 22 00 50.38 +84 44 36.5
Date_UT              unfiltmlim        MASTER_observatory
2019-04-26 20:56:51   20.0             MASTER-Tavrida
2019-04-26 20:38:02   19.7             MASTER-Kislovodsk
2019-04-26 16:25:18   19.5             MASTER-Tunka

There is a star in 4.3" in USNO-B1 (B1=20.77,R1=19.08) with proper motion .



The message may be cited.

M. Axelsson (KTH & Stockholm Univ.), E. Bissaldi (INFN and Politecnico Bari), D. Kocevski (NASA/MSFC), F. Longo (University and INFN, Trieste), and N. Omodei (Stanford Univ.) report on behalf of the Fermi-LAT Collaboration:

We have searched data collected by the Fermi Large Area Telescope (LAT) on April 26, 2019, for possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger S190426c (GCN 24237
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 ).

We define "instantaneous coverage" as the integral over the region of the LIGO probability map that is within the LAT field of view at a given a time, and "cumulative coverage" as the integral of the instantaneous coverage over time. Fermi-LAT had instantaneous coverage of ~85% of the LIGO probability at the time of the trigger (T0 = 2019-04-26 15:21:55.337 UTC), and reached ~95% cumulative coverage after ~4 ks. Due to the observing pattern of Fermi, the remaining area was not observed for more than 24 hours after the trigger time of the event.

We performed a search for a transient counterpart within the observed region of the 90% contour of the LIGO map in a fixed time window from T0 to T0 + 10 ks.

We also performed a search which adapted the time interval of the analysis to the exposure of each region of the sky, and no additional excesses were found.

Energy flux upper bounds for the fixed time interval between 100 MeV and 100 GeV for this search vary between 1e-10 and 3.2e-7 [erg/cm^2/s].

The Fermi-LAT point of contact for this event is Magnus Axelsson (magaxe@kth.se<mailto:magaxe@kth.se>).

The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.

Z. Kostrzewa-Rutkowska (SRON/RU), S. Hodgkin, A. Delgado, D.L. Harrison, M.
van Leeuwen, G. Rixon, A. Yoldas (IoA Cambridge), D. Eappachen, P.G. Jonker
(SRON/RU) on behalf of Gaia Alerts team report the discovery of a transient
candidate within the probability skymap of S190426c (LIGO/VIRGO
Collaboration GCN Circ. 24237
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 ):

---------------------------------------------------------------------------

Name      TNSid Date [TCB]          RaDeg DecDeg AlertMag URL

---------------------------------------------------------------------------

Gaia19boq AT2019egk
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  2019-04-27T19:35:33 319.09753 58.89088  18.67

      http://gsaweb.ast.cam.ac.uk/alerts/alert/Gaia19boq/

---------------------------------------------------------------------------


Acknowledgements: This work has made use of data from the European Space
Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by
the Gaia Data Processing and Analysis Consortium (DPAC,
https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC
has been provided by national institutions, in particular the institutions
participating in the Gaia Multilateral Agreement. ZKR, DE, and PGJ
acknowledge support from the European Research Council under ERC
Consolidator Grant agreement no 647208.

Tianrui Sun,Jian Chen,Lei Hu,Fan Li, Ye Yuan, Yanning Fu, Yue Chen.,Xuefeng Wu,Kelai Meng(PMO), Wen-xiong Li, Xinghan Zhang,Xiao-feng Wang(THU), Lifan Wang(PMO and TAMU)

We report the observations of the updated localization with GLADE(Dalya et al.,
2018, MNRAS, 479, 2374) catalogue of the gravitational event S190426c (The LIGO Scientific Collaboration and the Virgo Collaboration, GCN 24277
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 ,24237
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 ) with the Yaoan High Precision Telescope at Yaoan Observation Station(in Yunnan Province, China(101.1811�� E,25.528��N)), Purple Mountain Observatory.

We obtained images of 48 galaxies in Rc band with exposure time 120s and calibrated to the PPMX catalogue (Roeser, 2008) .No obvious transient has been identified. The list of the observed/inspected targets and its 5-sigma magnitude limit  is given below.

Object  |RA DEC |ObserveTime |MagLimit(err) 
2MASS_J00055155+8537092 | 00:05:51.000 +85:37:09.00 | 2019-04-27T17:31:10 | 18.40(0.070)
2MASS_J00060903+8426372 | 00:06:09.000 +84:26:37.00 | 2019-04-27T18:20:39 | 18.09(0.098)
2MASS_J00084951+8555097 | 00:08:49.000 +85:55:09.00 | 2019-04-27T18:25:25 | 18.05(0.075)
2MASS_J00092210+8506409 | 00:09:22.000 +85:06:40.00 | 2019-04-27T18:42:10 | 17.94(0.079)
2MASS_J00142097+8440183 | 00:14:20.000 +84:40:18.00 | 2019-04-27T16:57:51 | 18.26(0.060)
2MASS_J00143375+8524234 | 00:14:33.000 +85:24:23.00 | 2019-04-27T14:08:57 | 19.23(0.051)
2MASS_J00152318+8610254 | 00:15:23.000 +86:10:25.00 | 2019-04-27T15:49:52 | 18.71(0.080)
2MASS_J00171922+8412432 | 00:17:19.000 +84:12:43.00 | 2019-04-27T18:39:45 | 15.29(0.175)
2MASS_J00222807+8549554 | 00:22:28.000 +85:49:55.00 | 2019-04-27T17:20:49 | 18.35(0.092)
2MASS_J00224102+8601575 | 00:22:41.000 +86:01:57.00 | 2019-04-27T17:16:57 | 18.75(0.060)
2MASS_J00240580+8413520 | 00:24:05.000 +84:13:52.00 | 2019-04-27T17:35:09 | 18.10(0.096)
2MASS_J00264523+8444573 | 00:26:45.000 +84:44:57.00 | 2019-04-27T18:51:44 | 17.91(0.079)
2MASS_J00282377+8606093 | 00:28:23.000 +86:06:09.00 | 2019-04-27T18:58:44 | 18.16(0.070)
2MASS_J00310187+8420369 | 00:31:01.000 +84:20:36.00 | 2019-04-27T19:08:19 | 17.94(0.067)
2MASS_J00373257+8410452 | 00:37:32.000 +84:10:45.00 | 2019-04-27T19:20:07 | 17.76(0.096)
2MASS_J00415229+8422560 | 00:41:52.000 +84:22:56.00 | 2019-04-27T15:01:47 | 19.03(0.073)
2MASS_J00430464+8800328 | 00:43:04.000 +88:00:32.00 | 2019-04-27T16:41:03 | 18.64(0.114)
2MASS_J00431317+8418363 | 00:43:13.000 +84:18:36.00 | 2019-04-27T15:17:08 | 14.75(0.039)
2MASS_J00432208+8527102 | 00:43:22.000 +85:27:10.00 | 2019-04-27T17:46:45 | 18.43(0.079)
2MASS_J00434058+8446222 | 00:43:40.000 +84:46:22.00 | 2019-04-27T16:47:22 | 18.44(0.043)
2MASS_J00460455+8539449 | 00:46:04.000 +85:39:44.00 | 2019-04-27T19:01:09 | 17.74(0.100)
2MASS_J00520371+8523325 | 00:52:03.000 +85:23:32.00 | 2019-04-27T15:45:58 | 18.94(0.048)
2MASS_J00553194+8500374 | 00:55:31.000 +85:00:37.00 | 2019-04-27T18:32:40 | 18.16(0.073)
2MASS_J00592185+8521346 | 00:59:21.000 +85:21:34.00 | 2019-04-27T16:37:05 | 18.75(0.069)
2MASS_J00592917+8732280 | 00:59:29.000 +87:32:28.00 | 2019-04-27T14:59:21 | 19.35(0.082)
2MASS_J01135181+8724333 | 01:13:51.000 +87:24:33.00 | 2019-04-27T17:13:04 | 18.68(0.077)
2MASS_J01150199+8620395 | 01:15:01.000 +86:20:39.00 | 2019-04-27T17:42:01 | 18.03(0.096)
2MASS_J01160660+8459035 | 01:16:06.000 +84:59:03.00 | 2019-04-27T15:13:48 | 15.42(0.039)
2MASS_J01215684+8458118 | 01:21:56.000 +84:58:11.00 | 2019-04-27T18:01:34 | 17.86(0.142)
2MASS_J01230987+8524108 | 01:23:09.000 +85:24:10.00 | 2019-04-27T15:56:04 | 18.81(0.060)
2MASS_J01264881+8506094 | 01:26:48.000 +85:06:09.00 | 2019-04-27T17:01:44 | 18.32(0.074)
2MASS_J01333891+8532521 | 01:33:38.000 +85:32:52.00 | 2019-04-27T16:16:55 | 18.42(0.079)
2MASS_J19321273+8812473 | 19:32:12.000 +88:12:47.00 | 2019-04-27T18:15:51 | 18.58(0.084)
2MASS_J20412914+8626330 | 20:41:29.000 +86:26:33.00 | 2019-04-27T17:27:13 | 19.07(0.039)
2MASS_J20441724+8654219 | 20:44:17.000 +86:54:21.00 | 2019-04-27T16:23:13 | 18.77(0.076)
2MASS_J20522972+8611119 | 20:52:29.000 +86:11:11.00 | 2019-04-27T16:44:59 | 19.11(0.078)
2MASS_J21213146+8713544 | 21:21:31.000 +87:13:54.00 | 2019-04-27T18:22:59 | 18.31(0.054)
2MASS_J22120284+8552027 | 22:12:02.000 +85:52:02.00 | 2019-04-27T15:06:35 | 17.53(0.136)
2MASS_J22470787+8450298 | 22:47:07.000 +84:50:29.00 | 2019-04-27T19:22:26 | 17.98(0.061)
2MASS_J22544273+8544285 | 22:54:42.000 +85:44:28.00 | 2019-04-27T18:35:00 | 20.51(0.039)
2MASS_J22582128+8648054 | 22:58:21.000 +86:48:05.00 | 2019-04-27T18:05:31 | 18.38(0.076)
2MASS_J23091312+8512017 | 23:09:13.000 +85:12:01.00 | 2019-04-27T18:49:24 | 17.94(0.104)
2MASS_J23151704+8433526 | 23:15:17.000 +84:33:52.00 | 2019-04-27T19:05:59 | 18.13(0.096)
2MASS_J23193319+8758310 | 23:19:33.000 +87:58:31.00 | 2019-04-27T15:34:19 | 18.47(0.077)
2MASS_J23252375+8752450 | 23:25:23.000 +87:52:45.00 | 2019-04-27T16:53:54 | 18.55(0.064)
2MASS_J23345217+8527335 | 23:34:52.000 +85:27:33.00 | 2019-04-27T18:56:24 | 17.92(0.075)
2MASS_J23505702+8511090 | 23:50:57.000 +85:11:09.00 | 2019-04-27T18:44:35 | 17.95(0.085)
2MASS_J23574733+8500029 | 23:57:47.000 +85:00:02.00 | 2019-04-27T14:11:17 | 18.85(0.039)

[GCN OPS NOTE(07may19): Per author's request, the typo in the SUBJECT-line
was changed from "25c" to "26c".]

Igor Andreoni (Caltech), Shreya Anand (Caltech), Mansi Kasliwal (Caltech)

On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations

We report photometry and historical detections of the transient candidate Gaia19boq AT2019egk
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  (Kostrzewa-Rutkowska et al., GCN 24344
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 ).  

Previous detections are reported in the Pan-STARRS1 Data Release 2 database (Chambers et al., 2016) at coordinates consistent with Gaia19boq, suggesting outburst history. 

The following table summarizes the ZTF photometry of the source on the days near the gravitational wave event S190426c (LIGO and Virgo Collaboration, GCN 24237
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 ). 
----------------------------------------------------
Date (UTC) | filter |  mag  | err
----------------------------------------------------
2019-04-24 10:41:57.120 |  r  | >20.02 |  -
2019-04-27 08:29:28.320 |  g  | 18.88 | 0.04
2019-04-27 09:54:51.840 |  r  | 18.51 | 0.04
2019-04-28 08:28:10.560 |  g | 19.02 | 0.04

The Gaia19boq transient, dubbed also ZTF19aaslxmg, shows red color and rapid evolution within 2 days after the gravitational wave event S190426c (LIGO and Virgo Collaboration, GCN 24237
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 ).  The red color could be due to high Galactic extinction E(B-V) = 0.9733 magnitudes (Schlafly & Finkbeiner, 2011).  

We conclude that Gaia19boq AT2019egk
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  is a Galactic variable source unrelated with the gravitational wave event S190426c (LIGO and Virgo Collaboration, GCN 24237
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 ).

ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IIT-B, India; IIA, India; LJMU, UK; TTU USA and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert filtering and follow-up co-ordination is being undertaken by the GROWTH marshal system (Kasliwal et al. 2019).

H. Kumar, V. Karambelkar, V. Bhalerao, K Deshmukh, M. Khandagale (IITB), G.
C. Anupama, T. Stanzin, U. Stanzin (IIA) report on behalf of the GROWTH
collaboration:

We observed the field of GRAWITA_J215716.26+832239.4 reported by L. Izzo
et.al. (GCN 24340
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 ) at 2019-04-29T21:04:39.694 UT with the 0.7m GROWTH-India
telescope. The image was taken in r filter with 600 sec exposure. We did
not find any source at the specified position up to mag_lim ~ 19.8,
calibrated with PS1 photometry.

We also continued follow-up of the localisation region of the GW candidate
event S190426c (LVC et al. GCN 24168
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 , G. Waratkar et. al. GCN 24316
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 ) with
the GROWTH-India telescope in the northernmost part of the sky. We obtained
43 r-band overlapping images covering a total area of 12.1 square degrees,
with 8.9% probability of containing the GW counterpart on 20190428 and 16
r-band overlapping images covering a total area of 4.4 square degrees, with
4.1% probability of on 20190829. Exposures were 600 seconds long and
reached a typical depth of 20.5 magnitude. Data processing is underway. On
20190428 (20190429), these fields contain 313(104) galaxies from the GLADE
catalog and 10(4) galaxies from NED. No obvious transients were seen in the
NED galaxies.

The GROWTH India Telescope (GIT) is a 70-cm telescope with a 0.7 degree
field of view, set up by the Indian Institute of Astrophysics and the
Indian Institute of Technology Bombay with support from the Indo-US Science
and Technology Forum (IUSSTF) and the Science and Engineering Research
Board (SERB) of the Department of Science and Technology (DST), Government
of India (https://sites.google.com/view/growthindia/). It is located at the
Indian Astronomical Observatory (Hanle), operated by the Indian Institute
of Astrophysics (IIA).

A. Tohuvavohu (PSU), P.A. Evans (U. Leicester), J.A. Kennea (PSU),
S.B. Cenko (NASA/GSFC), S.D. Barthelmy (NASA/GSFC), A.P. Beardmore (U.
Leicester), A.A. Breeveld (UCL-MSSL), D.N. Burrows (PSU), S. Campana
(INAF-OAB), G. Cusumano (INAF-IASF PA),  A. D'Ai (INAF-IASFPA), P.
D'Avanzo (INAF-OAB), V.D'Elia(ASDC), S.W.K. Emery (UCL-MSSL),  P.
Giommi (ASI), C. Gronwall (PSU), D. Hartmann (U. Clemson), N. J.
Klingler (PSU), H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL),
A.Y. Lien (GSFC/UMBC), D. Malesani (DARK/NBI), F.E. Marshall
(NASA/GSFC), A. Melandri (INAF-OAB), J.A. Nousek (PSU), S.R. Oates (U.
Warwick), P.T. O'Brien (U. Leicester), J.P. Osborne (U. Leicester), C.
Pagani (U. Leicester), K.L. Page (U.Leicester), D.M. Palmer (LANL), M.
Perri (ASDC), J.L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU),
M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), E. Troja
(NASA/GSFC/UMCP) report on behalf of the Swift team:

The Neil Gehrels Swift Observatory UVOT and XRT instruments began pointed
galaxy-targeted followup of the LIGO/Virgo detected S190425z (LVC GCN. 24168)
at 2019-04-25 12:53 UT (T0+274 min), delayed due to a commanding gap.
The observations continued until 2019-04-26 20:15 UT, when they were aborted
to begin followup of S190426c (LVC GCN. 24237).

The completed campaign comprised ~400 fields, covering several hundred
of the most massive galaxies in the localization volume.

The Swift UVOT and XRT began pointed galaxy-targeted followup of the
LIGO/Virgo detected S190426c (LVC GCN. 24237) at 2019-04-26 17:45:00
UT (T0+142 min) and continued until T0+~48 hours.

The completed campaign comprised ~800 fields, covering >30% of the
galaxy-convolved localization region of the 'LALInference1' skymap.

The GW rapid followup observations have a nominal 80 s duration, and
are performed primarily with the u filter and with XRT in PC mode. The
average limiting magnitude achieved is ~18.6 in u, and  ~5 x 10^-12
erg s^-1 cm^-2 in soft X-rays (0.3-10 keV).

Analysis of the data is ongoing, and candidate counterparts will be
reported as found.

A list of observed fields, times, and associated target IDs can be found at
the following URL for these triggers and for all future GW followup:
http://www.swift.ac.uk/LVC/

We remind the community that all Swift data are public, and encourage their use.

This circular is an official product of the Swift team.

Z. Kostrzewa-Rutkowska (SRON/RU), S. Hodgkin, A. Delgado, D.L. Harrison, M.
van Leeuwen, G. Rixon, A. Yoldas (IoA Cambridge), D. Eappachen, P.G. Jonker
(SRON/RU) on behalf of Gaia Alerts team report the discovery of a transient
candidate within the probability skymap of S190426c (LIGO/VIRGO
Collaboration GCN 24237
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 ):

---------------------------------------------------------------------------

Name      TNSid Date [TCB]          RaDeg DecDeg AlertMag URL

---------------------------------------------------------------------------

Gaia19bpm AT2019ehs
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  2019-04-29T07:29:20 299.21327 61.65942 18.86

      http://gsaweb.ast.cam.ac.uk/alerts/alert/Gaia19bpm/

---------------------------------------------------------------------------


Acknowledgements: This work has made use of data from the European Space
Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by
the Gaia Data Processing and Analysis Consortium (DPAC,
https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC
has been provided by national institutions, in particular the institutions
participating in the Gaia Multilateral Agreement. ZKR, DE, and PGJ
acknowledge support from the European Research Council under ERC
Consolidator Grant agreement no 647208.

Igor Andreoni (Caltech), Eric Bellm (UW) report on behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations

 

We searched for Zwicky Transient Facility (ZTF) detections associated with Gaia19bpm AT2019ehs
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  (Kostrzewa-Rutkowska et al., GCN 24355
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 ) in the archive of ZTF alerts. ��A transient, dubbed ZTF19aaphkxx, was found at the location of Gaia19bpm.�� The transient was first detected in public ZTF data starting from 2019-04-08 (g = 18.66 +- 0.14) and it peaked around 2019-04-15 (g = 17.98 +- 0.08).

 

The optical transient was detected days before the gravitational wave event S190426c (LIGO and Virgo Collaboration, GCN 24237
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 ), therefore we exclude an association between Gaia19bpm AT2019ehs
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  and S190426c.

 

 

ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IIT-B, India; IIA, India; LJMU, UK; TTU USA and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019).

Y.-D. Hu, A. J. Castro-Tirado, (IAA-CSIC), A. F. Valeev and V. V. 
Sokolov (SAO-RAS), R. Sanchez-Ramirez (INAF-IAPS), X.-Y. Li, A. Ayala, 
E. Fernandez-Garcia and F. J. Aceituno (IAA-CSIC), I. Carrasco, A. 
Castellon and C. Perez del Pulgar (UMA), M. D. Caballero-Garcia 
(ASU-CAS), S. B. Pandey (ARIES), A. Garcia and S. Geier (GRANTECAN, IAC, 
ULL), on behalf of a larger collaboration, report:

Following the detection of the three new transients ZTF19aaslzjf, 
ZTF19aasmftm and ZTF19aasmddt (Perley et al., GCN 24331
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 ) within the 
error area of the GW event S190426c (LVC, GCN 24237
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 ), we observed the 
three targets with the 1.5m telescope at the Observatorio de Sierra 
Nevada (Spain) in the BVI-bands, starting on May 1, 02:01 UT. In 
addition, optical spectra for each target (1200s) covering the range 
3700-7500 A were obtained with the 10.4m GTC telescope equipped with 
OSIRIS in La Palma (Spain) starting on May 1, 02:30 UT.

ZTF19aaslzjf is found to be in the outskirts of its host galaxy and its 
spectrum is consistent with that of a type Ia SN at z= 0.086.

ZTF19aasmftm is found to be in the outskirts of its host galaxy and its 
spectrum is consistent with that of a type Ia SN few days before maximum 
at z = 0.156 (confirmed by the emission lines of the galaxy).

ZTF19aasmddt is found to be in the outskirts of its host galaxy at a 
redshift z = 0.028. The spectrum resembles that of a Type II SN at the 
same redshift before maximum.

Therefore none of these three newly reported ZTF transients seem to be 
related to the GW event S190426c.

We acknowledge the excellent support from the GTC staff.

R. Sanchez-Ramirez (INAF-IAPS), A. F. Valeev and V. V. Sokolov 
(SAO-RAS), Y.-D. Hu, A. J. Castro-Tirado, X.-Y. Li, A. Ayala, E. 
Fernandez-Garcia and F. J. Aceituno (IAA-CSIC), I. Carrasco, A. 
Castellon and C. Perez del Pulgar (UMA), D. Hiriart and W. H. Lee 
(UNAM), S. Jeong and I. H. Park (SKKU), A. Garcia and S. Geier 
(GRANTECAN, IAC, ULL), on behalf of a larger collaboration, report:

Following the detection of Gaia19boq (Kostrzewa-Rutkowska et al., GCN 
24344
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 ) within the error area of the GW event S190426c (LVC, GCN 24237
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 ), 
we observed the target with the 1.5m telescope at the Observatorio de 
Sierra Nevada (Spain) in the BVI-bands, starting on May 1, 04:07 UT. 
Complementary images I ugriZ were taken starting on May 1, 11:41 UT at 
the 0.6m BOOTES-5/JGT in Observatorio Nacional de San Pedro Martir 
(Mexico). In addition, an optical spectrum (900s) covering the range 
3700-7500 A was obtained with the 10.4m GTC telescope equipped with 
OSIRIS in La Palma (Spain) starting on May 1, 04:07 UT.

The Gaia19boq spectrum reveals strong Balmer lines in absorption, with 
the exception of a very weak H-alpha showing a P Cyg profile. All lines 
are redshifted ~400 km/s. Therefore we conclude that Gaia19boq is found 
to be a CVN star in outburst in our Galaxy and therefore unrelated to 
the GW event S190426c.

We acknowledge the excellent support from the GTC staff.

LIGO/Virgo S190426c: Update on Source Classification

The LIGO Scientific Collaboration and Virgo Collaboration report:

Based on posterior support from preliminary parameter estimation
[1,2], under the assumption that the candidate S190426c is
astrophysical in origin, the relative probabilities amongst
the signal categories NSBH : MassGap : BNS : BBH are revised
to be approximately 12 : 5 : 3 : 0.

Under the same assumption of astrophysical origin, we find
strong evidence that the lighter compact object has a
mass < 3 solar masses (HasNS: >99%) and a 72% probability
of having disrupted material outside the final compact object
(HasRemnant: 72%).

The probability of non-astrophysical origin and the false
alarm rate are not being updated at this time; both measures
of significance should be expected to change with offline analyses
and continued observations.

For further information about analysis methodology and the contents
of this alert, refer to the LIGO/Virgo Public Alerts User Guide
<https://emfollow.docs.ligo.org/userguide/>.

[1] Veitch, et al. PRD 91, 042003 (2015)
[2] Abbott, et al. PRL 116, 241102 (2016)

D. Svinkin, S. Golenetskii, R.Aptekar, D. Frederiks,
M. Ulanov, A. Tsvetkova, A. Lysenko, A. Kozlova, and T. Cline,
on behalf of the Konus-Wind team, report:

Konus-Wind (KW) was observing the whole sky at the time of the
LIGO/Virgo event S190426c (2019-04-26 15:21:55.337 UTC, hereafter T0;
LIGO/Virgo Collaboration GCN Circ. 24237
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 ).

No triggered KW event happened from ~7 days before and ~0.6 day
after T0. The closest waiting-mode event was ~12.5 hours before T0.
Using waiting-mode data within the interval T0 +/- 100 s,
we found no significant (> 5 sigma) excess over the background
in both KW detectors on temporal scales from 2.944 s to 100 s.

We estimate an upper limit (90% conf.) on the 20 - 1500 keV fluence
to 7.3x10^-7 erg/cm^2 for a burst lasting less than 2.944 s and having a
typical KW short GRB spectrum (an exponentially cut off power law with
alpha =-0.5 and Ep=500 keV). For a typical long GRB spectrum (the Band
function with alpha=-1, beta=-2.5, and Ep=300 keV), the corresponding
limiting peak flux is 2.0x10^-7 erg/cm^2/s (20 - 1500 keV, 2.944 s scale).

All the quoted values are preliminary.

LIGO/Virgo S190426c (BHNS candidate): Implications from Numerical Relativity

M. Ruiz, S. L. Shapiro and A. Tsokaros
report on behalf of the Illinois Relativity Group


Consistent with GCN 24411
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 , indicating that the LIGO/Virgo gravitational
wave source S190426c is a likely BHNS, the absence of a gamma-ray burst,
kilonova and other counterpart EM radiation agrees with recent GRMHD
simulations of BHNS mergers by our Illinois Relativity Group. In
Ruiz, Shapiro and Tsokaros (2018), PRD 98, 123017 (arXiv 1810.08618), the
group surveyed BHNS configurations with different initial mass ratios
q=BH:NS=3:1 and 5:1, BH spins a_{BH}/M_{BH}=-0.5, 0, 0.5, 0.75 and dipole
magnetic fields (aligned and tilted by 90 degrees with respect to the
orbital angular momentum). Only for initial a_{BH}/M_{BH}>=0.5 and
aligned B-fields did we find collimated, magnetically-confined jets
launched from the poles of the BH remnants following the peak GW signal.
Only in those cases did we find EM luminosities consistent with typical
sGRBs and significant mass outflows. For example, in our case q=5:1 and
a_{BH}/M_{BH}=0 the remnant disk and magnetic field were too small to
drive a jet and generate a significant mass outflow or counterpart EM
luminosity, hence no sGRB or kilonova.

S. B. Cenko (GSFC), S. Frederick (UMd), P. Gatkine (UMd), S. Dichiara (GSFC/UMd), E. Troja (GSFC/UMd), and L. P. Singer (GSFC) report on behalf of a larger collaboration:

We obtained a spectrum of the transient source ZTF19aassfws (Perley et al., GCN 24331
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 ) with the DeVeny spectrograph on the 4.3m Discovery Channel Telescope beginning at 10:07 UT on 2 May 2019.  The slit was centered on the nucleus of the host galaxy, SDSS J195440.25+611424.2.  The spectrum is dominated by a red stellar continuum, along with a series of nebular emission lines corresponding to a redshift of z = 0.093.  No clear evidence for broad emission lines or non-galaxy features are apparent.  For standard cosmological parameters, this corresponds to a luminosity distance of ~ 430 Mpc, consistent with the distance inferred from the gravitational wave emission (LVC et al., GCN 24237
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 ).

Christoffer Fremling (Caltech), Andrew Levan (Radboud),  Mansi Kasliwal
(Caltech) and Nial Tanvir (Leicester)

report on behalf of a larger collaboration

We imaged ZTF19aassfws (Perley et al. GCN 24331
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 , Coughlin et al. GCN 24283
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 )
with the INT on UT 2019-04-08. Difference imaging relative to PanSTARRS1
(Chambers et al. 2016) finds no detection in the r-band to r > 22.6 mag and
a bright detection in z-band at z ~ 20.8,corresponding to M_Z ~ -17.2 at
z=0.093 (Cenko et al. GCN24430
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 ). The z-band luminosity is higher than
GW170817 at this phase. The red color at this phase is plausible for a
kilonova but we cannot definitively rule out unrelated, nuclear activity.
We further caution that the INT and PS1 have different filter transmission
curves in z-band. We encourage follow-up to confirm or refute the
association of this source with the GW event S190426c (LVC et al. GCN
24237
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 ,  GCN 24411
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 ).

We thank the INT observers, Lord Dover and Tarik Zegmott for facilitating
these observations.

The correct UT date for the INT observations reported in Fremling et al.
GCN 24433
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  is 2019-05-08. Apologies for the typo.

Dillon Dong (Caltech), Gregg Hallinan (Caltech), Dale Frail (NRAO) and
Kunal Mooley (NRAO/Caltech) report:

The VLA Sky Survey observed a field containing the nuclear optical
transient  ZTF19aassfws (Perley et al., GCN 24331
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 ) on 2019-04-12 at UT
14:16:53, 14 days prior to the compact object merger candidate S190426c
(LVC et al.; GCN 24237
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 ). There is no archival 3GHz source at the
transient location, with a local 3 sigma upper limit of 390uJy. This
rules out a radio-luminous AGN with a specific luminosity greater than
9x10^28 erg/s/Hz at the spectroscopic redshift reported by Cenko (GCN
24430
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 ).

The VLA Sky Survey (VLASS) is a multi-epoch, 2-4 GHz survey with the
Karl G. Jansky Very Large Array (VLA) covering the full sky north of
declination = -40 degrees at ~2.5" resolution to a 1-sigma depth of
~120uJy/beam per epoch. Observations and data reduction for the VLASS
are carried out by staff of the National Radio Astronomy Observatory
(NRAO). The NRAO is a facility of the National Science Foundation
operated under cooperative agreement by Associated Universities, Inc.

Alessandra Corsi (TTU), Dale Frail (NRAO), Gregg Hallinan (Caltech), Kunal Mooley (Caltech/NRAO), Mansi Kasliwal (Caltech)
report on behalf of the JAGWAR collaboration:

We imaged the field of ZTF19aassfws (Perley et al. GCN 24331
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 , Cenko et al. GCN 24430
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 , Fremling et al. GCN 24433
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 , Dong et al. 
24440, Huber et al. GCN 24458
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 ), identified in the error region of the LIGO-Virgo event S190426c (LVC GCN 24237
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 , 24411
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 ), with 
the Karl G. Jansky Very Large Array (VLA) in its B configuration. Our observations started on 2019 May10 at 07:19:15 UT, ended 
on 2019 May 10 at 10:18:45 UT, and were carried out at a central frequency of about 2.8 GHz. Preliminary analysis shows no 
evidence for significant radio emission at the location of ZTF19aassfws. We thus constrain the radio flux density at the
location of the ZTF transient to be <~16 uJy (3 sigma). At z=0.093, this corresponds to a luminosity density <~3.5e27 erg/s/Hz.

We thank the NRAO staff for promptly executing these observations.

L. Rhodes, R. Fender, D. Williams, J. Bright (Oxford), K. Mooley (NRAO, Caltech; Jansky Fellow), A. Horesh (The Hebrew University of Jerusalem), D. Green, D. Titterington (MRAO) and the JAGWAR collaboration.

We observed the position of the reported GW190426c afterglow candidate: ZTF19aassfws (D. A. Perley et al. GCN 24331
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 ) with the AMI Large Array at a central frequency of 15.5GHz. We started observing on 2019 May 10.16 for 4 hrs. We find no significant radio emission at the coordinates of ZTF19aassfws and therefore report a 3 sigma upper limit of 177uJy.

We thank the MRAO staff for scheduling these observations.

Dheeraj Pasham (MIT), Keith Gendreau (NASA/GSFC), Zaven Arzoumanian
(NASA/GSFC), Stephen Eikenberry (UFL), Wynn C.G. Ho (Haverford) report on
behalf of the NICER team:

The transient ZTF19aassfws (Perley et al., GCN#24331
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 ) fell in the
LIGO/Virgo error box of the trigger S190426c (LVC et al., GCN#24237
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 ), and
Cenko et al. (GCN#24430
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 ) found that its distance is consistent with that
inferred from the gravitational wave signal. NICER observed this target for
7 ks, approximately half of which was in especially low background/high
sensitivity conditions.

We do not detect any X-ray emission above the background from this region.
Assuming an X-ray spectrum with a power-law index of 1.7 (similar to
GW170817) at a redshift of 0.093 with an absorbing column of 8e20 cm**-2
(Milky Way column), we estimate an upper limit on the unabsorbed 0.35-11.5
keV X-ray flux of 1.3e-13 erg/s/cm**2.

NICER can carry out prompt follow-up observations of transients and is
planning to systematically follow up alerts from LIGO/Virgo and other X-ray
bright extra-galactic transients in the future.

NICER is a 0.2-12 keV X-ray telescope operating on the International Space
Station. The NICER mission and portions of the NICER science team
activities are funded by NASA.

N. P. M. Kuin (UCL-MSSL), A. A. Breeveld (MSSL-UCL),  C. Gronwall (PSU),
F. E. Marshall (NASA/GSFC), S. R. Oates (Uni. of Warwick), M.J. Page
(UCL-MSSL),
M. de Pasquale (Istambul U), M. H. Siegel (PSU), A. D'Ai (INAF-IASFPA),
P. D'Avanzo (INAF-OAB), S. D. Barthelmy (NASA/GSFC), A. P. Beardmore (U.
Leicester),
D. N. Burrows (PSU), S. Campana (INAF-OAB), S. B. Cenko (NASA/GSFC),
G. Cusumano (INAF-IASF PA), V. D'Elia(ASDC), P. A. Evans (U. Leicester),
P. Giommi (ASI), D. Hartmann (Clemson U.), J. A. Kennea (PSU),
H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC), D. B. Malesani (DTU Space),
A. Melandri (INAF-OAB), J. A.  Nousek (PSU), P. T. O'Brien (U. Leicester),
J. P. Osborne (U. Leicester), C. Pagani (U. Leicester), K. L. Page
(U.Leicester),
D.M. Palmer (LANL), M. Perri (ASDC), J. L. Racusin (NASA/GSFC), T. Sakamoto
(AGU),
B. Sbarufatti (INAF-OAB/PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu
(PSU),
and E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift team:

The Swift UVOT instrument started follow up observations of the
LIGO-Virgo event S190426c (LVC GCN Circ. No. 24237) at 2019-04-26 17:45:00
UT
142 minutes after the event. Observations continued for about 48 hours
(Tohuvavohu et al., GCN Circ. No. 24353).

The UVOT approach for searching for the ultraviolet-optical counterpart has
been described in Kuin et al. (GCN Circ. No. 24767). The limiting magnitude
can vary but typically is 18.6th magnitude (Vega).  In the 894 fields that
were observed, UVOT detected 1008 galaxies and 130 counterpart candidates
but none of the counterpart candidates from the automated processing proved
to be a viable source. Neither did the additional inspection of the imaged
galaxies lead to a candidate missed by the automated processing.

The LIGO Scientific Collaboration and Virgo Collaboration report:

A revised computation of the classification of the candidate based on
detection-pipeline-specific foreground and background models is
available. The probability of the source being of terrestrial origin
is now estimated to be 58% in contrast to the original estimation of
14% in�� GCN Circular 24237
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 . This revision was necessitated by a
bug-fix in the source-classification code. This same bug-fix was used
to update the event candidate S190510g, as reported in GCN Circular
24462
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 . We apologize for the delay in updating the information for this
event.

The estimated false alarm rate is unchanged at 1.9e-08 Hz, or about
one per 1.6 years. Note that future offline analyses may infer a
different terrestrial probability and/or false alarm rate.

The new p_astro.json file in GraceDB at
https://gracedb.ligo.org/superevents/S190426c/ reports that the
revised classification of the candidate is Terrestrial (58%),
BNS (24%), MassGap (12%), NSBH (6%) and BBH (<1%). Note that the
parameter estimation based classification reported in GCN Circular
24411
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  is unchanged: Assuming that the candidate S190426c is
astrophysical in origin, the relative probabilities amongst the signal
categories NSBH : MassGap : BNS : BBH are approximately 12 : 5 : 3 : 0
based on posterior support.