LIGO/Virgo G298389

The LIGO Scientific Collaboration and Virgo report:

The LIB (Lynch et al., PRD 95, 104046) Burst analysis identified
candidate G298389 during real-time processing of data from LIGO
Hanford Observatory (H1) and LIGO Livingston Observatory (L1)
at 2017-08-19 15:50:46.990 UTC (GPS time: 1187193064.990).
Virgo was also taking data at this time in nominal condition.

G284239 is a low-significance short-duration burst candidate.
It is an event of interest because its false alarm rate, as
determined by the online analysis, is 1.56e-07 Hz or about one in 2
months, passing our stated alert threshold of ~1/month.
The event's properties can be found at this URL:
https://gracedb.ligo.org/events/G298389

No other GW event candidates were identified within a 300 s window
before or after G298389.

A sky map, LIB.fits.gz, is available to be retrieved from the
GraceDB event page. This is the preferred sky map at this time.
The 50% confidence region covers 252 squares degrees and the 90%
confidence region covers 799 square degrees.

Updates on our analysis of this event will be sent as they become
available.

M. Ageron (CPPM/CNRS), B. Baret (APC/CNRS), A. Coleiro (IFIC & APC), D. Dornic (CPPM/CNRS), A. Kouchner (APC/Universite Paris Diderot), T.
Pradier (IPHC/Universite de Strasbourg) report on behalf of the ANTARES Collaboration:

Using on-line data from the ANTARES detector, we have performed a follow-up analysis of the recently reported LIGO/Virgo G298389 event
using the updated LIB probability map at event time. The ANTARES visibility at the time of the alert together with the 90% contour 
of the probability map are shown in: https://www.cppm.in2p3.fr/~dornic/events/G298389/gw190817_visi.png <https://www.cppm.in2p3.fr/~dornic/events/G298389/gw190817_visi.png> (gwantares/GW@ANT32). Considering the location 
probability provided by the LIGO collaboration, there is only 6% chance that the GW emitter was in the ANTARES field of view.

No up-going muon neutrino candidate events were recorded in the ANTARES sky during a +/- 500s time-window centered on the G298389 event
time. The expected number of atmospheric background events in the region visible by ANTARES is ~1.1e-2 in the +/- 500s time window. An
extended search during +/- 1 hour gives no up-going neutrino coincidence.

The results of a second analysis covering the full-sky as well as an estimate of the upper limit on the associated neutrino fluence will be sent in a 
subsequent circular.

ANTARES, being installed in the Mediterranean Deep Sea, is the largest neutrino detector in the Northern Hemisphere.  It is primarily
sensitive to astrophysical neutrinos in the TeV-PeV energy range.  At 10 TeV, the median angular resolution for muon neutrinos is below 0.5 degrees.  
In the range 1-100 TeV, ANTARES has the best sensitivity to a large fraction of the Southern sky.

I. Bartos, S. Countryman (Columbia), C. Finley (U Stockholm), E. Blaufuss (U Maryland), R. Corley, Z. Marka, S. Marka (Columbia) on behalf of the IceCube Collaboration

In an analysis finished at 2017-08-19 19:07:25, we searched IceCube online track-like neutrino candidates (GFU) detected in a [-500,500] second interval about the LIGO-Virgo trigger G298389. We compared the candidate source directions of 6 temporally-coincident neutrinos to the LIB skymap, with the following parameters:

#            dt[s]     RA[deg]    Dec[deg]      E[TeV]  Sigma[deg]
------------------------------------------------------------------
1.          -29.47       104.5       -32.2       98.85         1.9
2.          -27.58        78.2        64.7        0.91         1.0
3.           28.18         7.7         1.8        3.87         0.3
4.          193.16       237.2         7.0        0.64         0.7
5.          434.75       122.5        -9.4        7.92         0.3
6.          477.83         0.3       -66.2      141.53         0.2


(dt--time from GW in [seconds]; RA/Dec--sky location in [degrees]; E--reconstructed secondary muon energy in [TeV]; Sigma--uncertainty of direction reconstruction in [degrees])

The analysis found NO COINCIDENT ONLINE TRACK-LIKE NEUTRINO CANDIDATES detected by IceCube within the 500 second window surrounding G298389 within the LIB skymap.

A coincident neutrino-GW skymap has been posted to GraceDB (<https://gracedb.ligo.org/apiweb/events/G298389/files/coinc_skymap_initial_icecube.png,0>). A JSON-formatted list of the above neutrinos can be downloaded from GraceDB at: <https://gracedb.ligo.org/apiweb/events/G298389/files/IceCubeNeutrinoList.json,0>

In addition, we are performing coincident searches with other IceCube data streams, including the high-energy starting events (HESE) and Supernova triggers.  HESE events have typical energies > 60 TeV and start inside the detector volume, leading to a relatively pure event sample with a high fraction of astrophysical neutrinos.  The SN trigger system is sensitive to sudden increases in photomultiplier counts across the detector, which could indicate a burst of MeV neutrinos.  We will submit separate GCN circulars if coincident HESE or SN triggers are found.

The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica.  For a description of the IceCube realtime alert system, please refer to <http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1610.01814
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 >; for more information on joint neutrino and gravitational wave searches, please refer to <http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1602.05411
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 >.

G. Piano (INAF/IAPS), F. Verrecchia (SSDC and INAF/OAR), A. Bulgarelli
(INAF/IASF-Bo), M. Pilia (INAF/OA-Cagliari), M. Cardillo (INAF/IAPS), M.
Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), C. Pittori (SSDC and
INAF/OAR), I. Donnarumma (ASI), F. Longo (Univ. Trieste and INFN Trieste),
A. Ursi, G. Minervini, A. Argan, Y. Evangelista (INAF/IAPS), F. Lucarelli
(SSDC and INAF/OAR), N. Parmiggiani, A. Zoli, V. Fioretti, F. Fuschino
(INAF/IASF-Bo), A. Trois (INAF/OA-Cagliari) M. Marisaldi (INAF/IASF-Bo and
Bergen University), A. Giuliani (INAF/IASF-Mi), report on behalf of the AGILE
Team:

In response to the LIGO/Virgo GW trigger event G298389 at T0 = 2017-08-19
15:50:46.990 UTC (GCN #21600
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 )  we performed an analysis of the AGILE Gamma-Ray
Imaging Detector
(GRID) data. At LIGO/Virgo trigger time (T0) the GRID exposure covered nearly
35% of the 90% c.l. LIGO/Virgo localization region (LR), observed at off-axis
angles between 45 and 70 deg.

An analysis of the data in the energy range 50 MeV - 10 GeV was performed
between -50 and +50 sec centered at T0.
Preliminary values of 3-sigma upper limits (UL) obtained within the accessible
LIGO/Virgo LR are:

from 6.0e-08 to 1.2e-06 erg cm^-2 s^-1 for integration time of 100s

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

C. Pittori, F. Verrecchia (SSDC and INAF/OAR), M. Cardillo (INAF/IAPS),
M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), G. Piano (INAF/IAPS),
M. Pilia (INAF/OA-Cagliari), A. Ursi (INAF/IAPS), A. Bulgarelli
(INAF/IASF-Bo), I. Donnarumma (ASI), F. Longo (Univ. Trieste and INFN
Trieste), G. Minervini, A. Argan, Y. Evangelista (INAF/IAPS), F. Lucarelli
(SSDC and INAF/OAR), N. Parmiggiani, A. Zoli, V. Fioretti, F. Fuschino
(INAF/IASF-Bo), A. Trois (INAF/OA-Cagliari) M. Marisaldi (INAF/IASF-Bo and
Bergen University),  A. Giuliani (INAF/IASF-Mi), report on behalf of the
AGILE Team:

In response to the LIGO/Virgo GW event G298389 (T0 = 2017-08-19 15:50:46.990
UTC; GCN #21600
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 ), a preliminary analysis of the AGILE MiniCALorimeter (MCAL)
data found no event candidates within a time interval covering approximately
-/+ 10 sec from the LIGO/Virgo T0, due to Earth occultation.

3-sigma ULs were computed for a 1 s integration time on different celestial
positions within the G298389 90% c.l. localization region, taking into
consideration the nearest triggered data acquisition (about 85 sec before
the T0), resulting in typical values of the fluence UL ranging from 5.4e^-7
erg cm^-2 to 6.3e^-7 erg cm^-2 (assuming as spectral model a power law with
photon index 1.4).

The AGILE-MCAL detector is a CsI detector with a 4-pi FoV, working in
the range 0.4 - 100 MeV. Additional analysis of AGILE data is in progress.

C. M. Hui (NASA/MSFC) reports on behalf of the GBM-LIGO Group:
L. Blackburn (CfA), M. S. Briggs (UAH), J. Broida (Carleton College),
E. Burns (NASA/GSFC), J. Camp (NASA/GSFC), T. Dal Canton (NASA/GSFC),
N. Christensen (Carleton College), V. Connaughton (USRA),
Adam Goldstein (USRA), R. Hamburg (UAH), P. Jenke (UAH),
D. Kocevski (NASA/MSFC), N. Leroy (LAL), T. Littenberg (NASA/MSFC),
J. McEnery (NASA/GSFC), R. Preece (UAH), J. Racusin (NASA/GSFC),
P. Shawhan (UMD), K. Siellez (GATech), L. Singer (NASA/GSFC),
J. Veitch (Birmingham), P. Veres (UAH), C. Wilson-Hodge (NASA/MSFC)

At the time of the LIGO/VIRGO candidate G298389, Fermi was passing
through the South Atlantic Anomaly; therefore the GBM detectors
were disabled.

Upper limits on persistent emission over 48-hour period centered on
the LIGO/VIRGO trigger time using the Earth Occultation technique
(Wilson-Hodge et al. 2012, ApJS, 201, 33) will be forthcoming when
data become available.

V. Savchenko (ISDC, University of Geneva, CH)
on behalf of the INTEGRAL group:
S. Mereghetti (IASF-Milano, Italy),
C. Ferrigno ((ISDC, University of Geneva, CH),
E. Kuulkers (ESTEC/ESA, The Netherlands),
A. Bazzano (IAPS-Roma, Italy), E. Bozzo,
T. J.-L. Courvoisier (ISDC, University of Geneva, CH)
S. Brandt (DTU - Denmark) R. Diehl (MPE-Garching, Germany)
L. Hanlon (UCD, Ireland) P. Laurent (APC, Saclay/CEA, France)
A. Lutovinov (IKI, Russia) J.P. Roques (CESR, France)
R. Sunyaev (IKI, Russia) P. Ubertini (IAPS-Roma, Italy)

We investigated serendipitous INTEGRAL observations carried out at the
time of the LIGO/Virgo burst candidate G298389.  The satellite was
pointing at RA=193.46 Dec=-25.644, 43 degrees from far from the peak
of high-probability area of LIGO localization. Depending on the
location within LIGO 90% confidence region the best upper limit is set
by the anti-coincidence shield of the spectrometer on board of
INTEGRAL (SPI/ACS), IBIS/ISGRI, or IBIS/PICsIT. The localization of
G298389 is not optimal for SPI-ACS observation, since part of the
localization it is occulted for SPI-ACS by the coded mask of IBIS. For
harder source spectra, IBIS, and especially IBIS/PICsIT reaches
sensitivity close to optimal in this orientation.

The INTEGRAL IBAS automatically inspects both ISGRI Field
of View and all-sky SPI-ACS light curve. It did not reveal any
significant excess above the background.

We investigated the SPI-ACS, IBIS/PICsIT, and IBIS/ISGRI light curves
between -500 and +500 s from the trigger time (2017-08-19 15:50:46
UTC) on temporal scales from 0.1 to 100 s, and found no evidence for
any significant deviation from the background.  We estimate a median
3-sigma upper limits in 90% LIGO localization region of 1.9e-6 erg/cm2
(75-2000 keV) assuming a duration of 8s and Band model parameters
alpha=-1, beta=-2.5, and E_ peak = 300 keV.  To derive a limit for a
typical short burst with 1 s duration, we use a harder cutoff power
law spectrum with a photon index of -0.5 and an Epeak = 500 keV. We
find a median limiting fluence of 4.0e-7 erg/cm2 (75-2000 keV) at 3
sigma c.l.

D. Kocevski (NASA/GSFC), S. Buson (NASA/GSFC), N. Omodei (Stanford), and G. Vianello (Stanford) report on behalf of the Fermi-LAT team: 

We searched data collected by the Fermi Large Area Telescope (LAT) for possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger G298389. At the time of the trigger (T0 = 2017-08-19 15:50:47.999, 524850652.999 MET), the Fermi gamma-ray space telescope was within the South Atlantic Anomaly (SAA).  During SAA passages the LAT does not collect data due to the high charged particle background in this region. The LAT resumed data taking upon exiting the SAA at roughly T0 + 460s,  At that time 26% of the LIGO/Virgo probability map was in the LAT field of view, and we reached 100% cumulative coverage within 9779 s after the trigger. 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 time, and "cumulative coverage" as the integral of the instantaneous coverage over time. 
We performed a search for a transient counterpart within the 90% contour of the LIGO/Virgo map in the time window from T0 to T0 + 10 ks, and no significant new sources are found. Similarly, the Automated Science Processing search, which looks for variation in flux from known sources and for new transients on a variety of time scales (Chiang 2012), did not detect any new transient consistent within the 90% contour of the G298389 map, during a six-hour interval from T0-3hr to T0+3hr.

The Fermi-LAT point of contact for this event is Daniel Kocevski (daniel.kocevski@nasa.gov) 

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.

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (NASA/GSFC), 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), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), 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), 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 G298389 (LIGO/VIRGO Collaboration GCN Circ. 21600
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 ),
where T0 is the LVC trigger time (2017-08-19T15:50:46.990 UTC).

The center of the BAT FOV at T0 is
RA  =  38.058 deg,
DEC = -48.841 deg,
ROLL = 102.747 deg.
The BAT Field of View (>10% partial coding) covers 0.0% of the integrated
LVC localization probability. That is, there is no overlap between the BAT
field of view and the LVC probability region at T0.

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,
respectively. 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 ~ 7.22 x 10^-8 erg/s/cm^2.

No event data are available within T0 +/- 100 s.
BAT retains decreased, but significant, sensitivity to rate increases for
gamma-ray events outside of its FOV. About 21.93% 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 of those within the FOV.

S. Sugita, N. Kawai (Tokyo Tech), M. Serino (RIKEN), H. Negoro (Nihon U.),
S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N.Isobe, R. Shimomukai (JAXA),
T. Mihara, M. Sugizaki, S. Nakahira, W. Iwakiri, M. Shidatsu, M.
Matsuoka (RIKEN),
T. Yoshii, Y. Tachibana, S. Harita, Y. Muraki, K. Morita (Tokyo Tech),
A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka, T. Hashimoto (AGU),
H. Tsunemi, T. Yoneyama (Osaka U.),
M. Nakajima, T. Kawase, A. Sakamaki (Nihon U.),
Y. Ueda, T. Hori, A. Tanimoto, S. Oda (Kyoto U.),
Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.),
M. Yamauchi, C. Hanyu, K, Hidaka (Miyazaki U.),
T. Kawamuro (NAOJ),
K. Yamaoka (Nagoya U.)
report on behalf of the MAXI team:

We examined the MAXI/GSC all-sky X-ray images (2-20 keV) obtained
in the orbit and the day after the LVC trigger
G298389 at 2017-08-19 15:50:46.990 UTC (GCN 21600
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 ).

GSC scanned more than 82% of the whole sky in the 92-min orbit,
which includes 76.3% of the 90% region in the LIB skymap
scanned from 16:29:17 to 16:47:45 UTC (T0+2310 to 3418 sec).
One day image obtained between 08-19 16:29:17 and 08-20 15:46:30 UTC
covers 86% of the 90% region in the LIB skymap.
No significant new source was found in these images
and the 2-20 keV averaged photon counts in the skymap region is 0.46 counts/sec.
The 1-sigma (3-sigma) averaged upper limits
obtained from the one-scan and one-day images in the LIB skymap are
11(33) and 3(9) mCrab, respectively
(see Serino et al., 2017 for the upper limit calculation).

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

I. Takahashi (IPMU), A. Yoshida, T. Sakamoto, Y. Kawakubo, M. Moriyama,
Y. Yamada, A. Tezuka, S. Matsukawa (AGU), K. Yamaoka (Nagoya U),
S. Nakahira (RIKEN), Y. Asaoka, S. Ozawa, S. Torii (Waseda U),
Y. Shimizu, T. Tamura (Kanagawa U), W. Ishizaki (ICRR), M. L. Cherry (LSU),
S. Ricciarini (U of Florence), A. V. Penacchioni, P. S. Marrocchesi (U of Siena)
and the CALET collaboration:

The CALET Gamma-ray Burst Monitor (CGBM) was operating at the trigger time
of G298389 (The LIGO Scientific Collaboration and Virgo Collaboration,
GCN Circ. 21600
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 ).  No CGBM on-board trigger occurred at the time
of the event.  Based on the LIGO localization sky map (LIB.fits.gz),
none of the probability area was in the field-of-view of the CGBM/HXM.
However, 13.4% of the summed probability was inside the field-of-view
of the CGBM/SGM.

Based on the analysis of the light curve data with 0.125 sec time resolution
from -60 sec to 60 sec from the trigger time, we found no significant excess
around the trigger time in either the HXM (7-3000 keV) or the SGM (40 keV -28 MeV)
data.

The CALET Calorimeter (CAL) was operating in low energy trigger mode at the
trigger time of G298389.  However, no LIGO high probability region was included
in the CAL's field of view at the time of the trigger.

I. Martinez-Castellanos (University of Maryland, College Park),
C. M. Hui (NASA/MSFC) and A.J. Smith (University of Maryland, College Park)
on behalf of the HAWC Collaboration:

HAWC Collaboration performed a follow-up of LIGO trigger G298389. At the
time
of the trigger no portion of the LV contour was visible to HAWC, so no
prompt
follow-up was possible.

The GW probability region transited through the HAWC FOV shortly after
trigger
time, with the maximum probability point (RA=158.0deg,Dec=1.6deg) entering
our FOV at T0 + 2 ks and leaving the FOV at T0 + 22 ks. We integrated this
period
and searched for highly significant events (94% of the probability was
covered).
There were no >5 sigma points observed during this transit. For a single
transit,
the 5 sigma sensitivity to a power law spectrum with a -2.5 index ranges
from
~1.7e-11 >1TeV cm^-2 s^-1 (~1 Crab units) at dec=15 to about 10 times
higher at
the edge of our FOV, dec=-25.

HAWC is a TeV gamma ray water Cherenkov array located in the state of
Puebla,
Mexico. It is sensitive to the energy range ~0.5-100TeV, and monitors 2/3
of the
sky every day with an instantaneous field-of-view of ~2 sr.

LIGO/Virgo G298389: Fermi GBM Flux Upper Limits

R. Hamburg (UAH) and C. Wilson-Hodge (NASA/MSFC) report on behalf of
the GBM-LIGO
Group:
L. Blackburn (CfA), M. S. Briggs (UAH), J. Broida (Carleton College), E.
Burns (NASA/GSFC), J. Camp (NASA/GSFC), T. Dal Canton (NASA/GSFC), N.
Christensen (Carleton College), V. Connaughton (USRA), A. Goldstein (USRA),
C. M. Hui (NASA/MSFC), P. Jenke (UAH), D. Kocevski (NASA/MSFC), N. Leroy
(LAL), T. Littenberg (NASA/MSFC), J. McEnery (NASA/GSFC), R. Preece (UAH),
J. Racusin (NASA/GSFC), P. Shawhan (UMD), K. Siellez (GA Tech), L. Singer
(NASA/GSFC), J. Veitch (Birmingham), P. Veres (UAH)

At the time of the LIGO/VIRGO candidate G298389, Fermi was passing through
the South Atlantic Anomaly, and the GBM detectors were disabled. We set the
following flux upper limits for the visible sky map within the 90% credible
region.

Using the Earth Occultation technique (Wilson-Hodge et al. 2012, ApJS, 201,
33) to estimate the amount of persistent emission during a 48-hour period
centered on the LIGO trigger time, we place the following range of 3-sigma
day-averaged flux upper limits based on observed sources over the entire
90% credible region of the LIGO sky map:

   Energy   min  max  median
    -----------------------------------
  12-27 keV:  0.09 0.22 0.14  Crab
  27-50 keV:  0.15 0.37 0.23  Crab
 50-100 keV:  0.22 0.55 0.33  Crab
100-300 keV:  0.39 1.02 0.60  Crab
300-500 keV:  2.69 7.59 4.20  Crab

These limits are based on the minimum requirement that each source in the
Earth Occultation catalog was Earth-occulted at least 6 times in each of
the 24 hour periods preceding and following the LIGO trigger and that the
occultations were well separated from nearby bright sources.

J. Alvarez-Muniz, F. Pedreira, E. Zas (Univ. Santiago de Compostela, Spain),
K. H. Kampert & M. Schimp (Bergische Universitat, Wuppertal, Germany)
on behalf of the Pierre Auger Collaboration.

In response to the LIGO/Virgo GW trigger G298389
(GCN #21600
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  ,T0=2017-08-19, 15:50:46.99 UTC):

We searched for Ultra High Energy (UHE) neutrinos with energies
above ~ 1e17 eV in data collected with the Surface Detector (SD) of
the Pierre Auger Observatory in a [-500,500] second interval about
the LIGO-Virgo trigger G298389 as well as 1 day after it.

NO events survived the cuts applied to reject the background due to UHE
Cosmic Rays i.e. NO neutrino candidates were detected.

The field of view (fov) where the SD of Auger is sensitive to UHE neutrinos
(corresponding to inclined directions with respect to the vertical relative
to the ground) was only marginally coincident with the LIGO 90%
localization
region at the time T0 of the merger alert. The LIGO 90% localization region
maximally overlapped with the Auger fov for the first time at ~ T0+6 hours
(i.e. ~ 6 hr after the merger) and remains fully in the Auger fov until
~ T0+7 hours.

The Pierre Auger Observatory is an UHE Cosmic Ray detector
located in the Mendoza Province in Argentina. It consists of an array
of Water Cherenkov detectors spread over a total surface of 3000 km^2
arranged in a triangular grid of 1.5 km side as well as Fluorescence
telescopes and other systems (see 10.1016/j.nima.2015.06.058
for more information).
For neutrino searches from GW events with Auger, please refer to:
https://journals.aps.org/prd/pdf/10.1103/PhysRevD.94.122007