GRB 131004A
GCN Circular 15303
Subject
GRB 131004A: Swift detection of a burst (may be short)
Date
2013-10-04T21:53:57Z (12 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
L. M. Z. Hagen (PSU), D. N. Burrows (PSU), V. D'Elia (ASDC),
N. Gehrels (NASA/GSFC), J. A. Kennea (PSU), V. Mangano (PSU),
F. E. Marshall (NASA/GSFC) and B. Sbarufatti (INAF-OAB/PSU) report on
behalf of the Swift Team:
At 21:41:03 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 131004A (trigger=573190). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 296.151, -2.960 which is
RA(J2000) = 19h 44m 36s
Dec(J2000) = -02d 57' 35"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a single-peaked
structure with a duration of about 2 sec. The peak count rate
was ~8500 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 21:42:13.4 UT, 70.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 296.11549, -2.95806 which is equivalent
to:
RA(J2000) = 19h 44m 27.72s
Dec(J2000) = -02d 57' 29.0"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 127 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.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (6.97 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 4.5
(+2.61/-2.22) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 75 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers none of
the XRT error circle. The 8'x8' region for the list of sources generated
on-board covers 100% of the BAT error circle. The list of sources is typically
complete to about 18 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.28.
Burst Advocate for this burst is L. M. Z. Hagen (lea.zernow.hagen AT gmail.com).
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.)
GCN Circular 15304
Subject
GRB 131004A: optical afterglow from the NOT
Date
2013-10-04T22:44:30Z (12 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@dark-cosmology.dk>
D. Xu, D. Malesani, J. Hjorth (DARK/NBI), P. Jakobsson (Univ. Iceland),
T. Kruehler (ESO Santiago), Nicolaas Groeneboom, and Anders Hafreager
(Univ. Oslo), report:
We observed the field of GRB 131004A (Hagen et al., GCN 15303) using the
NOT equipped with AlFOSC. Consistent with the XRT position, we detect a
new source at coordinates:
RA = 19:44:27.08
Dec = -02:57:30.2
The source is not visible in the DSS, and brighter than its limiting
magnitude, hence it is very likely the afterglow of GRB 131004A. At a
time of 0.43 hr after the GRB, we measure R = 20.2 +- 0.1 mag compared
to nearby USNO-B1 R2 magnitudes, where the error is mostly due to
calibration.
GCN Circular 15305
Subject
GRB 131004A: TNG optical afterglow confirmation
Date
2013-10-04T23:38:34Z (12 years ago)
From
Paolo D'Avanzo at INAF-OAB <paolo.davanzo@brera.inaf.it>
D. Malesani (DARK/NBI), P. D'Avanzo (INAF-OAB), L. di Fabrizio, G.
Tessicini (INAF-TNG) report on behalf of the CIBO collaboration:
We observed the field of the possible short GRB 131004A (Hagen et al. GCN
15303) with the Italian 3.6m TNG telescope located in Canary Islands,
equipped with the DOLoRes imager.
The optical candidate reported by Xu et al (GCN 15304) is clearly seen in
a 60 s R-band image taken at a mid t-t0=1.1 hours. From a preliminary
photometry we estimate for this source a magnitude of
R = 20.8 +/- 0.1 (calibrated against the USNOB1 catalogue).
Given the evidence of fading with respect to the report of Xu et al. (GCN
15304) we confirm this source as the optical afterglow of GRB 131004A. The
inferred power-law decay index is
alpha=0.59 +/- 0.15.
We acknowledge the TNG visitor astronomer X. Dumesque for support.
GCN Circular 15306
Subject
GRB 131004A: Liverpool Telescope optical afterglow observations
Date
2013-10-05T00:06:15Z (12 years ago)
From
Drejc Kopac at Math Phys U,Slovenia <drejc.kopac@fmf.uni-lj.si>
D. Kopac (U. Ljubljana), R. J. Smith (LJMU), C. G. Mundell (LJMU), N. R.
Tanvir (U. Leicester) and A. Gomboc (U. Ljubljana), on behalf of a large
collaboration report:
The 2-m Liverpool Telescope automatically began observing the field of GRB
131004A (Hagen et al., GCN 15303). We detect the optical afterglow in the
position consistent with the NOT (Xu et al., GCN 15304) and TNG (Malesani
et al., GCN 15305). Our preliminary photometry yields:
Mid time from Exp Filter Magnitude
trigger (min) (sec)
-------------------------------------------
85.1 300 i' 20.2 +- 0.1
111.3 300 i' 20.6 +- 0.1
-------------------------------------------
The magnitudes are calibrated agains I magnitudes of nearby USNO-B1.0
stars and are not corrected for the Galactic extinction.
GCN Circular 15307
Subject
GRB131004A: Magellan Redshift
Date
2013-10-05T00:56:31Z (12 years ago)
From
Ryan Chornock at Harvard <rchornock@cfa.harvard.edu>
R. Chornock, R. Lunnan, and E. Berger (Harvard) report:
We observed the optical afterglow (Xu et al., GCN 15304; Malesani et al., GCN
15305; Kopac et al., GCN 15306) of the possible short GRB 131004A (Hagen et al.,
GCN 15303) using LDSS-3 on the 6.5-m Magellan Clay Telescope. A sequence of
3x1200s spectroscopic exposures of the afterglow began at 23:44 on 4 October UT.
A preliminary reduction reveals a flat continuum with superposed weak emission
lines from [O II], H-beta, and [O III] at a common redshift of 0.717. Possible
weak features consistent with Ca II H+K absorption at this same redshift are
also present.
GCN Circular 15308
Subject
GRB 131004A: Enhanced Swift-XRT position
Date
2013-10-05T03:15:17Z (12 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester)
report on behalf of the Swift-XRT team.
Using 465 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 131004A, 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 = 296.11332, -2.95861 which is equivalent
to:
RA (J2000): 19h 44m 27.20s
Dec (J2000): -02d 57' 31.0"
with an uncertainty of 1.8 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.
GCN Circular 15309
Subject
GRB 131004A: GROND observations of the afterglow
Date
2013-10-05T08:38:02Z (12 years ago)
From
Sebastian Schmidl at TLS Tautenburg <schmidl@tls-tautenburg.de>
S. Schmidl, A. Nicuesa Guelbenzu, S. Klose (all TLS Tautenburg), and J.
Greiner (MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 131004A (Swift trigger 573190; Hagen et al.,
GCN 15303) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,
PASP 120, 405) mounted at the 2.2m MPG telescope at ESO La Silla
Observatory (Chile).
Observations started on October 4, 2013, at 23:41 UT, 2 hrs after the GRB
trigger. They were performed at an average seeing of 0".9 and at an
average airmass of 1.1.
The optical afterglow, discovered by Xu et al. (GCN 15304), is clearly
detected.
Based on a total exposure time of 460 s in g'r'i'z' and 480 s in JHK, at a
midtime of 2.75 hrs after the burst, we measure the following preliminary
AB magnitudes:
g' = 22.9 +/- 0.1,
r' = 22.1 +/- 0.1,
i' = 21.6 +/- 0.1,
z' = 21.4 +/- 0.1,
J = 20.2 +/- 0.2,
H = 20.2 +/- 0.2, and
K > 19.8 .
Given magnitudes are calibrated against GROND zeropoints as well as
2MASS field stars and are not corrected for the expected Galactic
foreground extinction corresponding to a reddening of E_(B-V)=0.29 mag
in the direction of the burst (Schlegel et al. 1998).
GCN Circular 15310
Subject
GRB131004A: TNG Redshift confirmation
Date
2013-10-05T09:32:49Z (12 years ago)
From
Valerio D'Elia at ASDC <delia@asdc.asi.it>
V. D'Elia (INAF-OAR/ASDC), P. D'Avanzo (INAF-OAB), D. Malesani (DARK/NBI),
L. di Fabrizio, G. Tessicini (INAF-TNG) report on behalf of the CIBO
collaboration:
We observed the optical afterglow (Xu et al., GCN 15304; Malesani et
al., GCN 15305; Kopac et al., GCN 15306) of the possible short GRB
131004A (Hagen et al., GCN 15303) using DOLORES/LR-B (wavelength
range: 3000-8000 AA) on the 4-m TNG Telescope at Canary islands. We
obtain a 1800 s spectrum starting at 2013-10-04 23:00:38 UT, i.e.,
1.33 hr from the burst.
A preliminary reduction reveals weak emission lines from [O II],
H-gamma and H-delta at a common redshift of 0.71.
We thus confirm the redshift reported by Chornock et al. (GCN 15307).
----------------------------------------------------------------
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GCN Circular 15311
Subject
GRB 131004A: Swift-XRT refined Analysis
Date
2013-10-05T11:54:05Z (12 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
C. Pagani (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A.
Maselli (INAF-IASFPA), D.N. Burrows (PSU), J.A. Kennea (PSU), V.
Mangano (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester)
and report on behalf of the Swift-XRT team: report on behalf of the
Swift-XRT team:
We have analysed 9.1 ks of XRT data for GRB 131004A, from 79 s to 34.7
ks after the BAT trigger. The data are entirely in Photon Counting
(PC) mode. the light curve is consistent with a constant source of
mean count rate 7.4e-02 ct/sec. A power-law fit gives an index of 0.1
(+2.0, -1.6).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.16 (+0.27, -0.26). The
best-fitting absorption column is 3.1 (+1.0, -0.9) x 10^21 cm^-2, in
excess of the Galactic value of 7.0 x 10^20 cm^-2 (Kalberla et al.
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 3.9 x 10^-11 (6.8 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 3.1 (+1.0, -0.9) x 10^21 cm^-2
Galactic foreground: 7.0 x 10^20 cm^-2
Excess significance: 4.7 sigma
Photon index: 2.16 (+0.27, -0.26)
If the light curve continues to decay with a power-law decay index of
0.1, the count rate at T+24 hours will be 0.029 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x
10^-12 (1.9 x 10^-12) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00573190.
This circular is an official product of the Swift-XRT team.
GCN Circular 15312
Subject
GRB 131004A: RATIR Optical and NIR Upper Limits
Date
2013-10-05T15:33:25Z (12 years ago)
Edited On
2024-11-07T18:52:07Z (7 months ago)
From
Owen Littlejohns at Az State U <olittlej@asu.edu>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Leo P. Singer at NASA/GSFC <leo.p.singer@nasa.gov>
Owen Littlejohns (ASU), Nat Butler (ASU), Alan M. Watson (UNAM),
Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G.
Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB), J. Xavier
Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UCSC),
Eleonora Troja (GSFC), Enrico Ramirez-Ruiz (UCSC), José A. de
Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM),
Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley
(GSFC) report:
We observed the field of GRB 131004A (Hagen, et al., GCN 15303) with the
Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the
1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on
Sierra San Pedro Mártir from 2013/10 5.12 to 2013/10 5.30 UTC (5.12
to 9.44 hours after the BAT trigger), obtaining a total of 2.17 hours
exposure in the r and i bands and 0.94 hours exposure in the Z,
Y, J, and H bands.
For a source within the Swift-XRT error circle, in comparison with 2MASS, we
obtain the following upper limits (3-sigma):
r > 23.91
i > 23.33
Z > 22.56
Y > 21.86
J > 21.81
H > 21.26
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. We did not detect the source
reported in Xu et al. (GCN 15304). In comparison with earlier GROND
observations (Schmidl, et al., GCN 15309) the source has faded by a minimum
of 1.7 magnitudes in the r band. This implies a power-law decay steeper
than t^-1.7.
We thank the staff of the Observatorio Astronómico Nacional in San Pedro
Mártir.
GCN Circular 15313
Subject
GRB 131004A: Swift/UVOT Detection
Date
2013-10-05T16:42:18Z (12 years ago)
From
MSSL Swift/UVOT team at MSSL/Swift <msslba@googlemail.com>
M. De Pasquale (UCL-MSSL) and L. M. Z. Hagen (PSU) report on behalf of the
Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 131004A
75 s after the BAT trigger (Hagen et al., GCN Circ. 15303).
A source consistent with the XRT position (Evans et al. GCN Circ. 15308)
and the position of the source given in Xu et al. (GCN Circ. 15304)
is detected in the initial and summed UVOT exposures.
The preliminary coordinates of this source are:
RA (J2000) = 19:44:27.09 = 296.11287 (deg.)
Dec (J2000) = -02:57:30.4 = -2.95844 (deg.)
with an estimated uncertainty of 0.55 arc sec. (radius, 90% confidence).
Preliminary detections and 3-sigma upper limits using the UVOT photometric
system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures
are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white_FC 75 225 147 19.23 �� 0.11
white 75 5688 520 20.18 �� 0.12
u_FC 288 537 246 19.96 �� 0.34
u 288 6715 659 20.72 �� 0.40
v 617 6100 432 >20.24
b 543 6770 285 >21.0
w1 666 6510 432 >20.9
m2 814 6305 413 >20.8
w2 593 5895 432 >21.0
The magnitudes in the table are not corrected for substantial Galactic
extinction
due to the reddening of E(B-V) = 0.28 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 15314
Subject
GRB 131004A: CARMA 93 GHz upper limit
Date
2013-10-05T19:11:45Z (12 years ago)
From
Ashley Zauderer at CfA <bevinashley@gmail.com>
B. A. Zauderer, E. Berger, W. Fong (Harvard) report on behalf of a larger
collaboration and the CARMA Key Project "A Millimeter View of the Transient
Universe":
"We observed the position of GRB 131004A (Hagen et al., GCN 15303) with
CARMA at a mean frequency of 93 GHz beginning 2013 October 5.04 (dt=3.4
hours). We do not find significant radio emission at the position of the
enhanced Swift-XRT and UVOT localizations (Evans et al., GCN 15308; De
Pasquale et al., GCN 15313), or the optical afterglow detection (Xu et al.,
GCN 15304), to a 3-sigma upper limit of ~0.3 mJy. No further radio
observations are planned.
We thank the CARMA staff for prompt execution of these observations."
GCN Circular 15315
Subject
GRB 131004A: Fermi GBM observation
Date
2013-10-06T02:20:22Z (12 years ago)
From
Shaolin Xiong at UAH <sx0002@uah.edu>
Shaolin Xiong (UAH)
reports on behalf of the Fermi GBM Team:
"At 21:41:03.68 UT on 04 October 2013, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 131004A (trigger 402615666 / 131004904),
which was also detected by the Swift/BAT (Hagen et al. 2013, GCN 15303).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 93 degrees.
The GBM light curve consists of multiple pulses
with a duration (T90) of about 1.4 s (50-300 keV).
The time-averaged spectrum from T0-0.19 s to T0+0.58 s is
well fit by a simple power law function with index -1.75 +/- 0.06.
The event fluence (10-1000 keV) in this time interval is
(6.2 +/- 0.6)E-7 erg/cm^2. The 64 ms peak photon flux measured
starting from T0+0.192 s in the 10-1000 keV band
is 10.4 +/- 1.6 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
GCN Circular 15316
Subject
GRB 131004A, Swift-BAT refined analysis
Date
2013-10-06T04:09:43Z (12 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
M. Stamatikos (OSU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
L. M. Z. Hagen (PSU), H. A. Krimm (GSFC/USRA), A. Y. Lien (NASA/GSFC/ORAU),
C. B. Markwardt (GSFC), J. Norris (BSU), D. M. Palmer (LANL),
T. Sakamoto (AGU), G. Sato (ISAS), J. Tueller (GSFC),
T. N. Ukwatta (MSU) (i.e. the Swift-BAT team):
Using the data set from T30 to T+62 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 131004A (trigger #573190)
(Hagen, et al., GCN Circ. 15303). The BAT ground-calculated position is
RA, Dec = 296.108, -2.952 deg which is
RA(J2000) = 19h 44m 26.0s
Dec(J2000) = -02d 57' 05.6"
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 73%.
The mask-weighted light curve shows a single short spike starts at ~T-0.18,
peaks at ~T0, and ends at ~T+1.35. T90 (15-350 keV) is 1.54 +- 0.33 sec
(estimated error including systematics).
The time-averaged spectrum from T-0.25 to T+1.80 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.81 +- 0.11. The fluence in the 15-150 keV band is 2.8 +- 0.2 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T-0.27 sec in the 15-150 keV band
is 3.4 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
The burst spectrum appears at the softer end of short bursts, which have
an average spectral index of 1.2 when fitting with a simple power-law model
(Sakamoto et al. 2011). The spectral lag for this burst is 0.130 s +- 0.020 s
(for the 50-100 keV and 15-25 keV bands), which is significantly longer
than those of regular short bursts.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/573190/BA/
GCN Circular 15317
Subject
GRB 131004A: Skynet PROMPT/DSO-14 upper limits
Date
2013-10-07T04:17:33Z (12 years ago)
From
Nathan Frank at U.North Carolina <nrfrank@live.unc.edu>
N. Frank, A. Trotter, D. Reichart, J. Haislip, A. LaCluyze, A. Smith, D. Caton, L. Hawkins, T. Berger, H. T. Cromartie, R. Egger, A. Foster, K. Ivarsen, M. Maples, J. Moore, M. Nysewander, E. Speckhard, and J. A. Crain report:
Skynet observed the Swift/XRT localization of the field of GRB 131004A (Hagen et al., GCN 15303, Swift trigger # 573190) with four 16" telescopes of the PROMPT array at CTIO, Chile and with the 14" telescope at the Appalachian State University Dark Sky Observatory (DSO), North Carolina, starting at 2013-10-04, 23:39:35 UT and continuing until 2013-10-05, 02:21:12 UT (t=1.9-4.7h post-trigger).
Skynet took a total of 220 160s exposures simultaneously in each of the BVRI bands. In stacked images, we do not detect any uncatalogued optical source in any band at or near the reported position. The 3-sigma limiting magnitudes of our images are:
==============================================
t(mean) telescope band exposures 3-sig lim mag
-------------------------------------------------------------------------
2.5h Prompt3 B 25x160s 18.98
2.7h Prompt1 V 32x160s 21.56
3.4h Prompt4 R 55x160s 21.85
3.5h Prompt5 I 50x160s 21.12
2.9h DSO-14 I 7x160s 18.46
==============================================
Magnitudes are in the Vega system, calibrated to five APASS stars in the field. Magnitudes have not been corrected for line-of-sight Milky Way dust extinction, with expected E(B-V)=0.28 (Schlegel et al. 1998).
No further Skynet observations are scheduled.
GCN Circular 15318
Subject
GRB 131004A: Correction to XRT refined analysis
Date
2013-10-07T07:09:57Z (12 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team,
There was a mistake in the "Swift-XRT refined analysis" circular (GCN
Circ. 15311) in which it was erroneously stated that the light curve was
consistent with a constant source. In fact, the light curve is decaying
as a power-law with an index of 1.01 (+/- 0.07). We apologise for any
confusion caused. As ever, the full light curve and related GRB products
are online at http://www.swift.ac.uk/xrt_products/00573190
This circular is an official product of the Swift-XRT team.
GCN Circular 15319
Subject
GRB 131004A: MOSFIRE NIR imaging
Date
2013-10-08T09:31:30Z (12 years ago)
From
Daniel Perley at Caltech <dperley@astro.caltech.edu>
D. A. Perley (Caltech) reports:
I imaged the location of GRB 131004A (GCN 15303) in Ks-band with MOSFIRE
on the Keck I telescope on the night of 2013-10-07 for a total
integration time of 291 seconds under good seeing conditions but some
cloud cover. The midpoint of the integration was 07:21 UT, 2.40 days
after the GRB.
At the location of the optical transient reported by Xu et al. (GCN
15304), no source is detected to a limiting magnitude of Ks > 20.6. The
nearest detected object to this location is a faint (Ks = 19.7), compact
source approximately 1.4 arcsec to the west, at RA=19:44:26.99,
dec=-02:57:30.15.
Given the moderate redshift of z=0.717 (Chornock et al., GCN 15307),
these results suggest either that the host of this event is a relatively
low-mass galaxy or that the GRB exploded outside the bulk of the stellar
light of its host. The >1.5 sec duration and significant lag reported
in the BAT refined analysis (Lien et al., GCN 15316) may suggest the
former interpretation is more likely.
I thank D. Malesani for providing the NOT image to verity the location
of the optical transient.