GRB 180512A

A. Rossi (INAF-OAS), J. Palmerio (IAP, Paris), J. Japelj (API, U. 
Amsterdam), D. Malesani (DAWN/NBI and DARK/NBI), N. R. Tanvir (Univ. 
Leicester), D. A. Kann (HETH/IAA-CSIC), J. P. U. Fynbo (DAWN/NBI), G. 
Pugliese (API, U. Amsterdam),  A. de Ugarte Postigo (HETH/IAA-CSIC and 
DARK/NBI), K. E. Heintz (Univ. Iceland and DAWN/NBI), and S. D. Vergani 
(GEPI/Obs. Paris) report on behalf of the Stargate Consortium:

We observed the Swift/XRT afterglow localization of GRB 180512A (Swift 
trigger 832119; Deich et al., GCN #22710
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 ) with the ESO VLT UT4 equipped 
with the HAWK-I near-infrared imager. Observations started on 2018 May 
13 at 04:27 UT and ended at 05:28 UT, for a total of 36 min on source 
and corresponding to a midtime of ~7 hours after the GRB trigger. We do 
not detect the optical source observed by Rossi et al. (GCN #22718
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 ), nor 
any other object within the XRT error circle, down to H > 22.8 (Vega), 
calibrated against 2MASS field stars.

Moreover, we note that after comparing the early GROND upper limit (r' > 
24.9; Bolmer, GCN #22714
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 ) with the Swift/XRT observations, we obtain an 
optical to X-ray spectral slope beta_OX < ~0.1 (using the convention 
F_nu ~ nu^-beta). This value is lower than the minimum expected 
following standard afterglow modelling (beta_OX >= 0.5) and, together 
with the r-band detection with LBT as well as the high X-ray column 
density (Burrows et al., GCN #22721
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 ), suggests that a combination of 
moderate redshift, intrinsic faintness and dust extinction is 
responsible for the faint optical afterglow.

We acknowledge the excellent support from the ESO staff, particularly 
Cyrielle Opitom, Fuyan Bian, and Steffen Mieske in obtaining these 
observations.

D.N. Burrows (PSU), A. Tohuvavohu (PSU), S.L. Gibson (U. Leicester), Z.
Liu (NAOC / U. Leicester), J.P. Osborne (U. Leicester), P. D'Avanzo
(INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), S. J. LaPorte
(PSU) and A. Deich report on behalf of the Swift-XRT team:

We have analysed 4.2 ks of XRT data for GRB 180512A (Deich et al. GCN
Circ. 22710
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 ), from 230 s to 72.7 ks after the  BAT trigger. The data
are entirely in Photon Counting (PC) mode. The enhanced XRT position
for this burst was given by Evans et al. (GCN Circ. 22715
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.87 (+0.12, -0.11).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.5 (+0.9, -0.8). The
best-fitting absorption column is  2.3 (+1.5, -1.1) x 10^22 cm^-2, in
excess of the Galactic value of 1.7 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 5.2 x 10^-11 (1.9 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.3 (+1.5, -1.1) x 10^22 cm^-2
Galactic foreground: 1.7 x 10^20 cm^-2
Excess significance: 3.6 sigma
Photon index:	     2.5 (+0.9, -0.8)

If the light curve continues to decay with a power-law decay index of
0.87, the count rate at T+24 hours will be 2.1 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x
10^-13 (4.0 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00832119.

This circular is an official product of the Swift-XRT team.

J. R. Cummings (CPI), S. D. Barthelmy (GSFC),
A. Deich (PSU), H. A. Krimm (NSF/USRA),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):

Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180512A (trigger #832119)
(Deich et al., GCN Circ. 22710
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 ).  The BAT ground-calculated position is
RA, Dec = 201.940, 21.404 deg which is
  RA(J2000)  =  13h 27m 45.5s
  Dec(J2000) = +21d 24' 15.7"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 67%.

The mask-weighted light curve shows a weak pulse that starts at ~T+30 s,
peaks at ~T+40 s, and ends at ~T+55 s. The short spike at T+54.4 s is due
to detector noise. T90 (15-350 keV) is 24.0 +- 7.1 sec (estimated error including systematics).
Note that the burst went out of the BAT FOV at T+469 s. The large pulse
seen in the BAT raw light curve from ~T+400 s to ~T+550 s was from a bright
background source that came in and out of the BAT FOV during this time interval.

The time-averaged spectrum from T+29.00 to T+55.00 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.10 +- 0.27.  The fluence in the 15-150 keV band is 4.2 +- 0.7 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+39.00 sec in the 15-150 keV band
is 0.6 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/832119/BA/

Alan M. Watson (UNAM), Nat Butler (ASU), Alexander Kutyrev (GSFC),

William H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J.
Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI),
Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz
(UCSC), Jes��s Gonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM), Harvey
Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (U. Wash.), and Vicki
Toy (UMD) report:

We observed the field of GRB 180512A (Deich et al., GCN Circ. 22710
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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 from 2018/05 13.16 to
2018/05 13.44 UTC (5.75 to 12.58 hours after the BAT trigger), obtaining
a total of 5.22 hours exposure in the r and i bands.

For a source within the enhanced Swift-XRT error circle (Evans et al.,
GCN Circ. 22715
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 ), in comparison with the SDSS DR9 and 2MASS catalogs, we
obtain the following 3-sigma upper limits:

 r	> 24.30
 i	> 24.23

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.

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

A. Rossi and E. Palazzi (INAF-OAS) report on behalf of the CIBO 
colaboration:

We  observed the field of GRB180512A (Swift trigger 832119; Deich et 
al., GCN #22710
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 ) simultaneously in r' and z' bands with the LBC imager 
mounted on LBT (Mt Graham, AZ, USA). Observations started at 04:05 UT on 
2018-05-13, 6 hrs after the GRB trigger and finished at 04:27 UT and 
allowed us to obtain 20min of exposure in each band.

Image inspection reveals a faint source within the Swift/XRT enhanced 
error circle (Evans et al., GCN 22715
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 ) with coordinates:
RA(J2000) = 13:27:45.130
Dec(J2000)= +21:24:13.39
with an uncertainty of 0.2" in each coordinate.

The source is detected only r'-band and has magnitude r' = 25.0 mag 
+-0.3 (AB), calibrated against r'-band SDSS field stars. No statement 
about the variability can be made at this point. Further observations 
are planned.

No correction for the expected Galactic foreground extinction
corresponding to a reddening of E_(B-V)=0.02 mag in the direction of the 
burst (Schlafly & Finkbeiner 2011) has been applied.

We acknowledge the excellent support from the LBT-INAF staff, 
particularly F. Cusano and A. Gargiulo in obtaining these observations.

N. P. M. Kuin (UCL-MSSL) and Deich (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 180512A
218 s after the BAT trigger (Deich et al., GCN Circ. 22710
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 ).  No optical
afterglow consistent with the XRT position (Evans et al. GCN Circ. 22715
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 )
is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC           218          368          147         >21.1
white              218         4358          344         >21.2
v                 5986         6120          132         >19.0
b                 3953         4153          197         >20.7
u                 3748        16254          422         >20.7
w1                3543        16019         1107         >20.3
m2                9380        10280          886         >20.9
w2                5781         5981          197         >20.1

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).

C. Guidorzi, R. Martone (U. Ferrara), S. Kobayashi (LJMU), C.G. Mundell 
(U. Bath), A. Gomboc (U. Nova Gorica), I.A. Steele (LJMU) on behalf of a 
large collaboration report:

The 2-m Liverpool Telescope automatically began observing Swift GRB 
180512A (Deich et al. GCN 22710
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 ) on May 12, 22:07:15 UT (5.5 minutes 
since the GRB) with the RINGO3 polarimeter and the IO:O camera in the 
SDSS-R filter. Within the enhanced XRT error circle (Evans et al. GCN 
22715
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 ) we do not detect any optical counterpart down to the following 
magnitude:

Mid time since GRB�������� Exp�������������� Filter���������������� Magnitude
(hrs)���������������������������������� (s)
-----------------------------------------------------------
0.64���������������������������������� 6x10������������ SDSS-R������������������ > 20.8
-----------------------------------------------------------

as calibrated against nearby SDSS objects.

P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 1368 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 180512A, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 201.93805, +21.40355 which is equivalent
to:

RA (J2000): 13h 27m 45.13s
Dec (J2000): +21d 24' 12.8"

with an uncertainty of 1.9 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

J. Bolmer MPE Garching) reports on behalf of the GROND Team:

I observed the field of GRB180512A (Swift trigger 832119; Deich et
al., GCN #22710
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 ) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2m MPG telescope at the ESO La Silla
Observatory (Chile).

Observations started at 00:03 UT on 2018-05-13, 2.7 hrs after the GRB
trigger. They were performed at an average seeing of 1.3'' and at an
average airmass of 1.9.

No source is detected within or close to the Swift-XRT error circle.

Based on 40 min of exposure in g'r'i'z' and 41 min in JHK_s, at a mid-time
of 00:44 UT, we derive the following preliminary upper
limits (in AB system):

g' > 25.4 mag,
r' > 24.9 mag,
i' > 24.0 mag,
z' > 23.4 mag,
J > 21.9 mag,
H > 21.2 mag, and
K_s > 20.2 mag.

Given upper limits are calibrated against SDSS field stars in g'r'i'z'
as well as 2MASS field stars in JHK_s. No correction for the expected Galactic
foreground extinction corresponding to a reddening of E_(B-V)=0.058 mag in
the direction of the burst (Schlafly & Finkbeiner 2011) has been applied.

Kasper Elm Heintz (Univ. Iceland and DAWN/NBI), Daniele Malesani (DAWN/NBI and DARK/NBI), Lauri Siltala (NOT), and Pilar Montanes Rodriguez (IAC), report on behalf of a larger collaboration:

We observed the field around GRB 180512A (Deich et al., GCN 22710
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 ) with the 2.5-m Nordic Optical Telescope (NOT) equipped with ALFOSC.

Observations of 3x100 s were carried out in each of the SDSS r, i, and z filters and started at 22:48:54 UT on May 12, 47 min after trigger. We do not detect the optical counterpart within the Swift-XRT error circle and calibrated against Pan-STARRS local photometry we measure upper limits (at 3-sigma) of:

m(r) > 23.3, m(i) > 23.0, and m(z) > 22.1 AB mag.

These magnitudes are not corrected for Galactic extinction in the direction of the GRB.

[GCN OPS NOTE(12may18): Per author's request, a typo in the author name Rodriguez was corrected.]

L. Izzo (HETH/IAA-CSIC) reports:

We observed the field of GRB 180512A (Deich et al., GCN Circ. 22710
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 ) with the 0.5m telescope of the Osservatorio Astronomico S. Di Giacomo located in Agerola, Italy ( http://acgo.it/oa )

We began observing at 22:31:54 UT (~30 min after the GRB trigger), and obtained 7x180s images in the Rc band. In our stacked image, we find no source inside the Swift-XRT error box down to a 3-sigma limit of Rc (Vega) > 20.2. The calibration was performed using nearby stars in the USNO B1 catalog.

A. de Ugarte Postigo (HETH/IAA-CSIC, Dark/NBI), L. Izzo, D. A. Kann 
(both HETH/IAA-CSIC), and A. Sota (IAA/CSIC) report on behalf of HETH:

We observed the field of GRB 180512A  (Deich et al.; GCN Circ. 22710
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 ) 
with the 1.5-m OSN telescope in Granada, Spain

Observations started at 22:15:35 UT (827 s after the GRB trigger) for 
OSN, and we obtained 8x60s images in the Rc band and 6x300s images in 
the Ic band. Observations were obtained in inclement conditions (bad 
seeing of ~3").

In our stacked images, we find no source inside the Swift-XRT error 
circle down to a 3-sigma limit of Ic (Vega) > 21. The calibration was 
performed using nearby stars in the SDSS catalog.

A. Deich (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
J.D. Gropp (PSU), S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC) and
F. E. Marshall (NASA/GSFC) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 22:01:47 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180512A (trigger=832119).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 201.953, +21.406 which is 
  RA(J2000) = 13h 27m 49s
  Dec(J2000) = +21d 24' 23"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 550 sec.  The main pulse starts at
~T+400 s and ends at ~T+550 s. The peak count rate
was ~1000 counts/sec (15-350 keV), at ~500 sec after the trigger. 

The XRT began observing the field at 22:05:20.1 UT, 213.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 201.93846, 21.40271 which is equivalent
to:
  RA(J2000)  = 13h 27m 45.23s
  Dec(J2000) = +21d 24' 09.8"
with an uncertainty of 4.4 arcseconds (radius, 90% containment). This
location is 50 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper.  We
cannot determine whether the source is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.73
x 10^20 cm^-2 (Willingale et al. 2013). 

No UVOT data are available at this time. 

Burst Advocate for this burst is A. Deich (aud375 AT psu.edu). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)