GRB 150811A
GCN Circular 18141
Subject
GRB 150811A: Continued RATIR Observations
Date
2015-08-14T20:01:44Z (10 years ago)
From
Nat Butler at UC berkeley <natxbutler@gmail.com>
Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William
H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (UCB), J. Xavier Prochaska
(UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC), Eleonora Troja
(GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jos�� A. de
Diego (UNAM), Leonid Georgiev (UNAM), Jes��s Gonz��lez (UNAM), Carlos
Rom��n-Z����iga (UNAM), Neil Gehrels (GSFC), Harvey Moseley (GSFC), John
Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report:
We observed the field of GRB 150811A (Evans, et al., GCN 18119) 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 2015/08 14.22 to 2015/08 14.41 UTC (73.12 to
77.68 hours after the BAT trigger), obtaining a total of 3.56 hours
exposure in the r, i, and z bands.
In comparison with the USNO-B1 and 2MASS catalogs, we obtain the following
detections and upper limit (3-sigma):
r = 22.4 +/- 0.3
i = 22.0 +/- 0.4
z > 20.37
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. The fading of the source remains
consistent with t^(-1) (see, Butler et al., 18120, 18132, 18140).
We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.
GCN Circular 18140
Subject
GRB 150811A: Continued RATIR Observations
Date
2015-08-13T19:28:24Z (10 years ago)
From
Nat Butler at Az State U <natbutler@asu.edu>
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
(ORAU/GSFC), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico
Ramirez-Ruiz (UCSC), Jos���� A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes����s
Gonz����lez (UNAM), Carlos Rom����n-Z��������iga (UNAM), Neil Gehrels (GSFC), and
Harvey Moseley (GSFC) report:
We observed the field of GRB 150811A (Evans, et al., GCN 18119) 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 2015/08 13.14 to 2015/08 13.40 UTC (47.37 to
53.59 hours after the BAT trigger), obtaining a total of 4.93 hours
exposure in the r, i, and z bands.
We continue to detect the optical afterglow. Relative to the flux reported
in Butler et al. (GCN 18132), the source continues to appear to fade
approximately as t^(-1). In comparison with the USNO-B1 and 2MASS
catalogs, we obtain the following detections and upper limit (3-sigma):
r = 22.00 +/- 0.20
i = 21.83 +/- 0.20
z > 20.40
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.
GCN Circular 18135
Subject
GRB 150811A: KAIT Refined Analysis
Date
2015-08-12T21:40:27Z (10 years ago)
From
Xiang-Gao Wang at GuangXi U <wangxg@gxu.edu.cn>
Xianggao Wang (UC Berkeley, GXU, UNLV), WeiKang Zheng and
Alexei V. Filippenko (UC Berkeley) report on behalf of the
KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT) at
Lick Observatory responded to Swift GRB 150811A (Evans et al.,
GCN 18119) starting at 04:09:05 UT, 176 s after the burst.
Observations were performed with an automatic sequence in the
V, I, and clear (roughly R) filters, and the exposure time was
20 s per image. Due to a focus problem, the first useful image
started at about 364 s after burst, and observations lasted
about 5.5 hours later. The optical afterglow (Butler et al.,
GCN 18120; GCN 18132, Zheng et al., GCN 18121, Kuin et al., GCN
18122; 18131, Japelj et al., GCN 12123, Perley & Cenko, GCN 12125,
Moskivitin, GCN 12128) was well detected in I filters.
We confirm the peak of the OT around ~13 m reported by
Perley & Cenko (GCN 12125). After 3 ks after the burst, the
light curve can be fit by a power law with index of -1.02,
consistent with the value reported by Butler et al. (GCN 18132).
A preliminary light curve is posted at:
http://astro.berkeley.edu/~zwk/grb/GRB150811A/GRB150811A_kait.png
GCN Circular 18134
Subject
GRB 150811A: VLA Detection
Date
2015-08-12T20:11:53Z (10 years ago)
From
Tanmoy Laskar at Harvard U <tanmoylaskar@gmail.com>
T. Laskar (NRAO / UC Berkeley), A. Zauderer, K. Alexander, E. Berger
(Harvard), and W. Fong (Univ. of Arizona) report on behalf of a larger
collaboration:
"We observed GRB 150811A (Evans et al; GCN 18119) at multiple frequencies
with the VLA beginning 2015 August 12.13 UT (0.96 days after the burst). At
a mean frequency of 21.8 GHz, we detect a radio source with a preliminary
flux density of ~ 0.1 mJy at
RA = 19:25:21.3920 +/- 0.0005
Dec = -15:25:31.00 +/- 0.01
consistent with the enhanced Swft/XRT position (Goad et al.; GCN 18124) and
the optical position (Butler et al., GCN 18120; Zheng at al., GCN 18121;
Kuin et al., GCN 18122). Follow-up observations are planned."
GCN Circular 18132
Subject
GRB 150811A: Continued RATIR Observations
Date
2015-08-12T18:18:04Z (10 years ago)
From
Nat Butler at UC berkeley <natxbutler@gmail.com>
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
(ORAU/GSFC), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico
Ramirez-Ruiz (UCSC), Jos�� A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes��s
Gonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM), Neil Gehrels (GSFC), and
Harvey Moseley (GSFC) report:
We observed the field of GRB 150811A (Evans, et al., GCN 18119) 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 2015/08 12.15 to 2015/08 12.41 UTC (23.39 to
29.66 hours after the BAT trigger), obtaining a total of 4.98 hours
exposure in the r, i, and z bands.
We continue to detect the source we reported earlier (Butler, et al.; GCN
18120), which we also observed for several additional hours on the first
night. In comparison with the USNO-B1 and 2MASS catalogs, we obtain the
following detections and upper limit (3-sigma):
r 21.68 +/- 0.14
i 21.48 +/- 0.05
z >18.9
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. In comparison with our previous
observations, the source flux has declined approximately as t^(-1).
We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir. Further observations are planned.
GCN Circular 18131
Subject
GRB 150811A: Swift/UVOT further observations
Date
2015-08-12T12:14:43Z (10 years ago)
From
Paul Kuin at MSSL <npkuin@gmail.com>
N. P. M. Kuin (UCL-MSSL) and P. A. Evans (U Leicester)
report on behalf of the Swift/UVOT team:
We report further on the Swift/UVOT observations of GRB 150811A which
began 148 s after the BAT trigger (Evans et al., GCN Circ. 18119).
A source consistent with the XRT position (Goad et al. GCN Circ. 18124)
was reported earlier in the optical/ir by Butler et al.(GCN Circ. 18120)
Zheng et al. (GCN Circ. 18121), Kuin et al.(GCN Circ. 12122), Japelj et
al., (GCN Circ. 12123), Perley and Cenko (GCN. Circ. 12125), Moskivitin
(GCN Circ. 12128). Our initial observations in the white filter show a
rise from the start at 147s around magnitude (white) 21 which continues
in the u band event data and starts leveling off around magnitude 17.8
550s after the trigger, consistent with the report by Perley and Cenko.
The data taken during the next orbit show that the decay had already
set in. The uv bands showed marginal count rates in all three bands
initially below the 3-sigma level, suggesting the burst is at low redshift.
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 148 297 147 20.39 +/- 0.23
u_FC 306 549 239 18.19 +/- 0.11
white 4424 4624 197 19.16 +/- 0.07
u 5449 5854 197 18.83 +/- 0.16
v 4835 5034 197 18.89 +/- 0.17
b 4219 4419 197 19.31 +/- 0.14
w1 5244 11888 1082 >20.6
m2 5039 10981 1082 >21.1
w2 4630 6265 393 >20.5
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.17 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 18129
Subject
GRB 150811A: Swift-BAT refined analysis
Date
2015-08-11T22:09:07Z (10 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC),
J. R. Cummings (GSFC/UMBC), P. A. Evans (U Leicester),
N. Gehrels (GSFC), 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 150811A (trigger #651882)
(Evans, et al., GCN Circ. 18119). The BAT ground-calculated position is
RA, Dec = 291.347, -15.434 deg which is
RA(J2000) = 19h 25m 23.3s
Dec(J2000) = -15d 26' 00.8"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 67%.
The mask-weighted light curve shows a single FRED-like pulse that starts
at ~T+1 s, peaks at ~T+6 s, and ends at ~T+40 s. T90 (15-350 keV)
is 34.00 +- 6.25 sec (estimated error including systematics).
The time-averaged spectrum from T+1.51 to T+40.36 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
2.13 +- 0.27. The fluence in the 15-150 keV band is 4.9 +- 0.8 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+6.59 sec in the 15-150 keV band
is 0.5 +- 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/651882/BA/
GCN Circular 18128
Subject
GRB 150811A: SAO RAS optical observations
Date
2015-08-11T21:44:15Z (10 years ago)
From
Moskvitin Alexander at SAO RAS <mosk@sao.ru>
A. S. Moskvitin (SAO RAS, Russia) report on behalf
of larger GRB follow-up collaboration:
The field of the GRB 150811A (Evans et al., GCNC #18119)
was observed with the Zeiss-1000, 1-m telescope of SAO RAS.
The observations started since 13.6 hours after the trigger.
6 x 300 sec frames in Rc filter were obtained under the
good weather conditions.
The OT (Butler et al., GCNC #18120; Zheng, Wang and Filippenko,
GCNC #18121; Kuin and Evans, GCNC #18122; Japelj, Guidorzi
and Kobayashi, GCNC #18123; Perley and Cenko, GCNC #18125)
is clearly detected in our stack image close to USNO-B1.0
star 0745-0762543. PSF photometry of the OT with DAOPHOT package
gives R = 20.74 +/- 0.12 (T_mid - T0 = 13.911 hours).
Photometry is based on the nearby USNO-B1 stars (R2 magnitudes).
The magnitude of the OT is not corrected for the Galactic extinction.
GCN Circular 18127
Subject
GRB 150811A: Swift-XRT refined Analysis
Date
2015-08-11T16:21:02Z (10 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
D.N. Burrows (PSU), C. Pagani (U. Leicester), A.P. Beardmore (U.
Leicester), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia
(ASDC), T.G.R. Roegiers (PSU), L.M. McCauley (PSU) and P.A. Evans
report on behalf of the Swift-XRT team:
We have analysed 8.5 ks of XRT data for GRB 150811A (Evans et al. GCN
Circ. 18119), from 128 s to 27.8 ks after the BAT trigger. The data
comprise 156 s in Windowed Timing (WT) mode (the first 9 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Goad et al.
(GCN Circ. 18124).
The light curve can be modelled with an initial power-law decay with an
index of alpha=2.52 (+/-0.19), followed by a break at T+366 s to an
alpha of 1.17 (+0.06, -0.10).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.11 (+0.21, -0.13). The
best-fitting absorption column is 1.60 (+0.65, -0.07) x 10^21 cm^-2,
consistent with the Galactic value of 1.5 x 10^21 cm^-2 (Willingale et
al. 2013). The PC mode spectrum has a photon index of 2.03 (+0.13,
-0.15) and a best-fitting absorption column of 2.1 (+1.0, -0.6) x 10^21
cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 3.5 x 10^-11 (4.9 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 2.1 (+1.0, -0.6) x 10^21 cm^-2
Galactic foreground: 1.5 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index: 2.03 (+0.13, -0.15)
If the light curve continues to decay with a power-law decay index of
1.17, the count rate at T+24 hours will be 3.2 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x
10^-13 (1.6 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/00651882.
This circular is an official product of the Swift-XRT team.
GCN Circular 18125
Subject
GRB 150811A: P60 Observations
Date
2015-08-11T13:46:42Z (10 years ago)
From
S. Bradley Cenko at NASA/GSFC <brad.cenko@nasa.gov>
D. A. Perley (DARK) and S. B. Cenko (GSFC) report:
The Palomar 60-inch automated telescope responded to the trigger for GRB 150811A (Evans et al., GRB 18119) and began observations at 04:10:54 UT, 4.75 minutes after the burst. A sequence of four 60-second i-band images was acquired, followed by a repeating cycle of 60-second r, i, and z-band images, then two epochs of imaging in ri filters later in the night.
The optical afterglow (e.g. Butler et al, GCN 18120; Zheng et al., GCN 18121; Kuin et al., GCN 18122; Japelj et al., GCN 18123) shows a sharp rise in flux during the first few observations, from I ~ 17.5 mag at t_mid = 5.25 minutes to a peak of I ~ 16.2 mag at t = 12.42 minutes (calibrating to USNO B1 I-band standards). Afterwards it levels out and then declines steadily, reaching I ~ 18.3 mag at t = 135.1 min and I ~ 19.0 mag at t = 303.85 min, corresponding to an average decay rate of approximately alpha = 0.8.
Further follow-up is planned. Spectroscopy is highly encouraged.
GCN Circular 18124
Subject
GRB 150811A: Enhanced Swift-XRT position
Date
2015-08-11T13:18:27Z (10 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1486 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 150811A, 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 = 291.33914, -15.42545 which is equivalent
to:
RA (J2000): 19h 25m 21.39s
Dec (J2000): -15d 25' 31.6"
with an uncertainty of 2.5 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 18123
Subject
GRB 150811A: LCOGT-McDonald afterglow detection
Date
2015-08-11T08:48:37Z (10 years ago)
From
Jure Japelj at U. of Ljubljana,Slovenia <jure.japelj@fmf.uni-lj.si>
J. Japelj (U. Ljubljana), C. Guidorzi (U. Ferrara), S. Kobayashi (LJMU)
on behalf of a large collaboration report:
We observed the position of GRB 150811A (Evans et al. GCN Circ.
18119) with the 1-m McDonald telescope (Fort Davis, US), a
member of the Las Cumbres Observatory network. Observations
started on August 11 at 06:13:35 UT, i.e., 127 minutes after
the GRB trigger time and were done with the r' and i' filters.
We detect the optical afterglow (Butler et al. GCN 18120, Zheng
et al. GCN 18121, Kuin et al. 18122) with the magnitude of
r' = 18.4 +- 0.2 at 132 min after the GRB trigger. Magnitude has
been calibrated against nearby USNOB-1 stars.
GCN Circular 18122
Subject
GRB 150811A: Swift/UVOT Detection
Date
2015-08-11T08:02:52Z (10 years ago)
From
Paul Kuin at MSSL <npkuin@gmail.com>
Paul Kuin (MSSL/UCL) and P. A. Evans (U Leicester)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 150811A
147 s after the BAT trigger (Evans et al., GCN Circ. 18119). A source
consistent with the XRT position and the optical transient reported
by Butler et al.(GCN Circ. 18120) and Zheng et al. (GCN Circ. 18121)
is detected in the promptly available UVOT exposures.
The preliminary UVOT position is:
RA (J2000) = 19:25:21.4
Dec (J2000) = -15:25:31.1
with an estimated uncertainty of 0.6 arc sec. (radius, 90% confidence).
The transient source is at a distance of 4.6 arcsec of a weak nearby
source.
Preliminary detections for the White and U finding charts 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 147 297 147 20.43 +/- 0.23
u_FC 306 549 241 18.24 +/- 0.11
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.17 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 18121
Subject
GRB 150811A: KAIT optical candidate
Date
2015-08-11T05:06:41Z (10 years ago)
From
Weikang Zheng at UC Berkeley <weikang@berkeley.edu>
WeiKang Zheng (UC Berkeley), Xianggao Wang (UC Berkeley, GXU, UNLV)
and Alexei V. Filippenko (UC Berkeley) report on behalf of the
KAIT GRB team:
The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at
Lick Observatory, responded to Swift GRB 150811A (Evans et al.,
GCN 18119) about 10 minutes after the burst. Observations were
performed with an automatic sequence in the clear (roughly R), V,
and I filters, and the exposure time was 20 s per image.
Inside the XRT error circle we detected an un-cataloged source with
coordinates of :
RA = 19:25:21.40 (J2000)
DEC= -15:25:30.96 (J2000)
The object has I band mag of ~16.5 at ~15 minutes after
burst and is decaying. We suggest this is the afterglow of GRB 150811A.
Follow-up observations are encouraged.
GCN Circular 18120
Subject
GRB 150811A: RATIR Optical Afterglow Detection
Date
2015-08-11T04:49:37Z (10 years ago)
From
Nat Butler at Az State U <natbutler@asu.edu>
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
(ORAU/GSFC), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico
Ramirez-Ruiz (UCSC), Jos�� A. de Diego (UNAM), Leonid Georgiev (UNAM), Jes��s
Gonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM), Neil Gehrels (GSFC), and
Harvey Moseley (GSFC) report:
We observed the field of GRB 150811A (Evans, et al., GCN 18119) 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 2015/08 11.17 to 2015/08 11.19 UTC (2.6
minutes to 0.47 hours after the BAT trigger), obtaining a total of 0.36
hours exposure in the r, i, and z bands.
We detect a highly-time-variable uncatalogued source within Swift-XRT error
circle. In comparison with the USNO-B1 catalog, we obtain the following:
r 17.51 +/- 0.01
i 17.22 +/- 0.01
z 16.76 +/- 0.04
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. The source is located at RA, Dec =
19:25:21.40, -15:25:30.2 (J2000, +/-0.5").
We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir. Further observations are planned.
GCN Circular 18119
Subject
GRB 150811A: Swift detection of a burst
Date
2015-08-11T04:21:01Z (10 years ago)
From
Kim Page at U.of Leicester <klp5@leicester.ac.uk>
P. A. Evans (U Leicester), A. Y. Lien (GSFC/UMBC) and
K. L. Page (U Leicester) report on behalf of the Swift Team:
At 04:06:09 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150811A (trigger=651882). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 291.371, -15.438 which is
RA(J2000) = 19h 25m 29s
Dec(J2000) = -15d 26' 16"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a weak complex
peak structure with a duration of about 20 sec. The peak count rate
was ~1000 counts/sec (15-350 keV), at ~3 sec after the trigger.
The XRT began observing the field at 04:08:30.6 UT, 141.6 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 291.33917, -15.42535 which
is equivalent to:
RA(J2000) = 19h 25m 21.40s
Dec(J2000) = -15d 25' 31.3"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 119 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 1.54
x 10^21 cm^-2 (Willingale et al. 2013).
The initial flux in the 2.5 s image was 4.59e-10 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 147 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 100% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag.
The 8'x8' region for the list of sources generated on-board covers 100% of the
XRT 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
0.17.
Burst Advocate for this burst is P. A. Evans (pae9 AT star.le.ac.uk).
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.)