GRB 120804A
GCN Circular 13573
Subject
GRB 120804A: Swift detection of a short burst
Date
2012-08-04T01:07:03Z (13 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
A. Y. Lien (NASA/GSFC/ORAU), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), S. T. Holland (STScI), J. A. Kennea (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL),
B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf
of the Swift Team:
At 00:54:14 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120804A (trigger=529686). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 233.929, -28.761 which is
RA(J2000) = 15h 35m 43s
Dec(J2000) = -28d 45' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a fast double-peaked
structure with a duration of about 1.5 sec. The peak count rate
was ~15000 counts/sec (15-350 keV), at ~0.5 sec after the trigger.
The XRT began observing the field at 00:55:47.8 UT, 93.6 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 233.94815, -28.78102 which is
equivalent to:
RA(J2000) = 15h 35m 47.56s
Dec(J2000) = -28d 46' 51.7"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 94 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 (9.29 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 1.9
(+1.89/-1.67) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 96 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 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 0.23.
Burst Advocate for this burst is A. Y. Lien (yarleen 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 13577
Subject
GRB 120804A: Enhanced Swift-XRT position
Date
2012-08-04T06:42:04Z (13 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester)
report on behalf of the Swift-XRT team.
Using 797 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 120804A, 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 = 233.94813, -28.78248 which is equivalent
to:
RA (J2000): 15h 35m 47.55s
Dec (J2000): -28d 46' 56.9"
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 13579
Subject
GRB 120804A: GROND upper limits
Date
2012-08-04T09:07:02Z (13 years ago)
From
Vladimir Sudilovsky at MPE <vsudilov@mpe.mpg.de>
V. Sudilovsky, J. Elliott, and J. Greiner (all MPE Garching) report
on behalf of the GROND team:
We observed the field of GRB 120804A (Swift trigger 529686; Lien et al.,
GCN 13573) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,
PASP 120, 405) mounted at the 2.2 m MPG/ESO telescope at La Silla
Observatory (Chile).
Observations started at 02:22 UT on 2012-08-04, 1.5 hrs after the GRB
trigger. We do not detect any sources within the XRT position reported by
Osborne et al (GCN 13577). We do note that observations were severely
limited by unfavorable weather conditions, including moon-illuminated
visible cirrus towards the field.
Based on six co-added exposures of 370s (g'r'i'z') and 240s (JHK) taken
at a mean airmass of 1.3 and a mean seeing of 3.0", we derive the following
upper limits (all AB system):
g' > 21.9
r' > 22.1
i' > 22.0
z' > 21.9
J' > 20.6
H' > 20.0
K' > 19.5
The magnitudes are derived based on GROND zeropoints (g'r'i'z') and 2MASS
stars (JHK). The above upper limits are not corrected for the Galactic
extinction
of E(B-V) = 0.23 mag along the line of sight (Schlegel et al. 1998).
GCN Circular 13580
Subject
GRB 120804A: Swift-XRT refined Analysis
Date
2012-08-04T13:07:05Z (13 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
M.C. Stroh (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), C.
Pagani (U. Leicester), A.P. Beardmore (U. Leicester), A. Melandri
(INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), G. Stratta (ASDC), J.A.
Kennea (PSU) and A.Y. Lien report on behalf of the Swift-XRT team:
We have analysed 9.2 ks of XRT data for GRB 120804A (Lien et al. GCN
Circ. 13573), from 78 s to 28.8 ks after the BAT trigger. The data
comprise 33 s in Windowed Timing (WT) mode (the first 8 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 Osborne et
al. (GCN. Circ 13577).
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.11 (+/-0.03).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.98 (+0.21, -0.20). The
best-fitting absorption column is 3.5 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 9.3 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 4.3 x 10^-11 (7.0 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 3.5 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 9.3 x 10^20 cm^-2
Excess significance: 5.3 sigma
Photon index: 1.98 (+0.21, -0.20)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00529686.
This circular is an official product of the Swift-XRT team.
GCN Circular 13581
Subject
GRB 120804A: Swift-BAT refined analysis
Date
2012-08-04T13:20:44Z (13 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
W. H. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
A. Y. Lien (NASA/GSFC/ORAU), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (OSU),
J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
Using the data set from T-240 to T+962 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 120804A (trigger #529686)
(Lien, et al., GCN Circ. 13573). The BAT ground-calculated position is
RA, Dec = 233.951, -28.768 deg, which is
RA(J2000) = 15h 35m 48.1s
Dec(J2000) = -28d 46' 06.1"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 24%.
The mask-weighted light curve shows two overlapping peaks starting
at ~T-0.2 sec, peaking at ~T+0.1 and ~T+0.5 sec, and ending at ~T+1.0 sec.
T90 (15-350 keV) is 0.81 +- 0.08 sec (estimated error including systematics).
The time-averaged spectrum from T-0.16 to T+0.83 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.34 +- 0.08. The fluence in the 15-150 keV band is 8.8 +- 0.5 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.16 sec in the 15-150 keV band
is 10.8 +- 0.6 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/529686/BA/
GCN Circular 13582
Subject
GRB 120804A: Swift/UVOT Upper Limits
Date
2012-08-04T13:40:29Z (13 years ago)
From
Margaret Chester at PSU <chester@astro.psu.edu>
M. M. Chester (PSU) and A. Y. Lien (NASA/GSFC/ORAU)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 120804A
97 s after the BAT trigger (Lien et al., GCN Circ. 13573).
No optical afterglow consistent with the XRT position (Osborne et al.,
GCN Circ. 13577) 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) exposures and subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white_FC 97 247 147 >21.4
u_FC 310 560 246 >20.7
white 97 5665 453 >22.0
v 640 6077 432 >20.6
b 566 6706 243 >20.9
u 310 6692 659 >21.3
w1 689 6487 413 >20.3
m2 4646 6282 393 >21.3
w2 4237 5872 393 >21.0
The magnitudes in the table are not corrected for the Galactic
extinction
due to the reddening of E(B-V) = 0.23 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 13584
Subject
GRB 120804A: MITSuME Okayama Optical upper limits
Date
2012-08-05T00:54:39Z (13 years ago)
From
Daisuke Kuroda at OAO/NAOJ <dikuroda@oao.nao.ac.jp>
D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ),
S. Nagayama (NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto)
and N. Kawai(Tokyo Tech)
report on behalf of the MITSuME collaboration:
We observed the field of GRB 120804A (Lien et al., GCNC 13573)
with the optical three color (g', Rc and Ic) CCD camera attached
to the MITSuME 50cm telescope of Okayama Astrophysical Observatory.
The observation started on 2012-08-04 11:04:43 UT (~10.2 h after the burst)
We did not find any new point source within the enhanced XRT circle
(Osborne et al., GCNC 13577) in all the three bands.
Three sigma upper limits of the OT are listed below. We used
GSC2.3 catalog for flux calibration.
T0+[day] MID-UT T-EXP[sec] g' Rc Ic
------------------------------------------------------
0.46585 12:05:03 6240.0 >19.9 >19.8 >19.1
------------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]
GCN Circular 13585
Subject
GRB 120804A: Swift-BAT Spectral lag analysis
Date
2012-08-05T03:36:54Z (13 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
J. Norris (BSU), N. Gehrels (GSFC), S. D. Barthelmy (GSFC)
We report the spectral lag analysis for GRB 120804A (GCN Circ. 13573 & 13581)
based on the BAT data. Using 8-ms binned light curves, the spectral lag
for the 15-25 keV to 50-100 keV bands is 16 +-12 msec, and -5 +-6 msec
for the 25-50 keV to 100-350 keV bands for both peaks combined.
These lag values place this burst in the short burst category.
GCN Circular 13586
Subject
GRB 120804A: Gemini-North observations
Date
2012-08-05T05:57:28Z (13 years ago)
From
Ryan Chornock at Harvard <rchornock@cfa.harvard.edu>
R. Chornock and E. Berger (Harvard) report on behalf of a larger
collaboration:
We observed the position of the X-ray afterglow of the short GRB 120804A
(Lien et al., GCN 13573) using GMOS on the Gemini-North 8-m telescope.
Observations began at 05:47 UT on 2012 August 4 (approximately 4.9 hours
after the BAT trigger). We obtained 11x180s of observations in both the
r and i filters. We find a pair of faint sources in the i band
observations within the enhanced XRT position (Osborne et al., GCN
13577) with coordinates (J2000):
S1: 15:35:47.48, -28:46:56.2
S2: 15:35:47.53, -28:46:57.6
with astrometric errors of about 0.3" relative to 2MASS. S1 is slightly
brighter than S2 in i. Neither source is detected in r. Further
observations are planned in order to search for variability of these
sources.
We thank the Gemini staff, particularly Chad Trujillo, for their
assistance with these observations.
GCN Circular 13587
Subject
GRB 120804A: EVLA Detection
Date
2012-08-05T15:06:22Z (13 years ago)
From
Ashley Zauderer at CfA <bevinashley@gmail.com>
W. Fong, A. Zauderer, E. Berger (Harvard) report on behalf of a larger
collaboration:
"We observed the position of the short GRB 120804A (Lien et al., GCN
13573) with the EVLA at 5.8 GHz beginning 2012 Aug 4.97 UT (dt=0.93 d
after the trigger). We detect a radio source within the Swift-XRT error
circle (Osborne et al., GCN 13577) at the position
RA 15:35:47.49 (+/- 0.01)
Dec -28:46:56.7 (+/- 0.1)
Followup observations are planned."
GCN Circular 13601
Subject
GRB 120804A: ATCA 34GHz upper limit
Date
2012-08-07T03:17:14Z (13 years ago)
From
Paul Hancock at U of Sydney <hancock@physics.usyd.edu.au>
P. Hancock, T. Murphy, B. Gaensler, M. Bell, D. Burlon (University of
Sydney/CAASTRO), A. de Ugarte Postigo (IAA-CSIC, DARK/NBI)
We observed GRB120804A (GCN 13573) with the Australia Telescope
Compact Array at 34GHz for 56 minutes centered on 04:35UT Aug 06 2012
(T0+2.15days).
We detect no radio source at the location of the GRB afterglow seen by
the EVLA (GCN 13587) and place a 3sigma upper limit of 200uJy on the
flux of an afterglow at 34GHz.
Further observations are planned.
These observations were obtained as part of ATCA project C2689. We
thank the observatory staff for their support and scheduling the
observations. The Australia Telescope is funded by the Commonwealth of
Australia for operation as a National Facility managed by CSIRO.
[GCN OPS NOTE(07aug12): Per author's request, the "120824A" in the Subject-line
was changed to "120804A".]
GCN Circular 13606
Subject
GRB 120804A: Gemini-North detection of an optical afterglow and putative host galaxy
Date
2012-08-07T16:04:57Z (13 years ago)
From
Wen-fai Fong at CFA <wfong@cfa.harvard.edu>
W. Fong, R. Chornock, and E. Berger (Harvard) report:
"We re-observed the location of the short-duration GRB 120804A (GCN
13573) with the Gemini Multi-Object Spectrograph (GMOS) mounted on the
Gemini-North 8-meter telescope to check for the presence of a fading
optical source. We obtained 16x180-sec of i-band observations in good
seeing conditions (FWHM=0.65") starting on 2012 August 07.30 UT, 3.3
days after the BAT trigger and 3.0 days after our initial observations
(GCN 13586).
Digital image subtraction of the two GMOS epochs using the ISIS
software package reveals a fading source slightly offset from the
center of S1, suggesting this to be the optical afterglow of GRB
120804A. There are no additional residuals in or around the refined
XRT position (improved upon from GCN 13577;
http://www.swift.ac.uk/xrt_positions/00529686/). Both S1 and S2 appear
to be extended, indicating that S1 is likely to be the
host galaxy of GRB 120804A and S2 is likely unrelated to the GRB.
We thank the Gemini staff for their assistance with these
observations."
GCN Circular 13611
Subject
GRB 120804A: ATCA 34GHz upper limit
Date
2012-08-08T10:29:43Z (13 years ago)
From
Paul Hancock at U of Sydney <hancock@physics.usyd.edu.au>
P. Hancock, T. Murphy, B. Gaensler, M. Bell, D. Burlon (University of
Sydney/CAASTRO), A. de Ugarte Postigo (IAA-CSIC, DARK/NBI)
We observed GRB120804A (GCN 13573) with the Australia Telescope
Compact Array at 34GHz for 96 minutes centered on 04:35UT Aug 08 2012
(T0+4.15days).
We detect no radio source at the location of the GRB afterglow seen by
the EVLA (GCN 13587) and place a 3sigma upper limit of 120uJy on the
flux of an afterglow at 34GHz.
These observations were obtained as part of ATCA project C2689. We
thank the observatory staff for their support and scheduling the
observations. The Australia Telescope is funded by the Commonwealth of
Australia for operation as a National Facility managed by CSIRO.
GCN Circular 13614
Subject
GRB 120804A: Konus-Wind and Swift/BAT joint spectral analysis
Date
2012-08-09T19:48:56Z (13 years ago)
From
Valentin Pal'shin at Ioffe Inst <val@mail.ioffe.ru>
T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC),
W. Baumgartner (GSFC/UMBC), J. Cummings (GSFC/UMBC),
E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), D. Palmer (LANL), G. Sato (ISAS),
M. Stamatikos (OSU), J. Tueller (GSFC), and T. Ukwatta (MSU)
on behalf of the Swift-BAT team,
V. Pal'shin, S. Golenetskii, R.Aptekar, E. Mazets, D. Frederiks, and
T. Cline on behalf of the Konus-Wind team,
report:
The short GRB 120804A (Swift/BAT trigger #529686: Lien et al., GCN Circ.
13573, Baumgartner et al. GCN Circ. 13581) triggered Konus-Wind at
T0=3255.749 s UT (00:54:15.749), but since the incident angle on the
triggered detector was 99.2 deg (i.e. the burst accidentally triggered
the S2 detector which observes the northern ecliptic hemisphere,
although the burst came from the southern ecliptic hemisphere: b = -9.2
deg) the standard analysis of the Konus-Wind spectral data is impossible.
To derive the broad-band spectral parameters of this burst, we performed
joint spectral analysis of the Swift/BAT data and the Konus-Wind
3-channel spectral data (obtained in the waiting mode from the detector
S1), which covers the energy range from 24 keV to 1.4 MeV.
The time intervals of the spectral data are chosen for the Konus-Wind
from T0(BAT)-0.916 s to T0(BAT)+2.028 s (single KW bin which comprises
the burst) and for the Swift/BAT from T0(BAT)-0.16 s to T0(BAT)+0.83 s
(that is the BAT T100 interval), where T0(BAT) is the trigger time of
BAT at 00:54:14.18 UTC. The energy ranges which we used in the joint
spectral analysis are 24-1400 keV and 14-150 keV for the Konus-Wind and
the Swift/BAT respectively. The spectral data of the two instruments
are fitted with the spectral model multiplied by a constant factor to
take into account the systematic effective area uncertainties in the
response matrices of each instrument and the difference in the chosen
intervals.
The spectrum is well fitted with a power-law with exponential cutoff
model: dN/dE ~ E^{alpha}*exp(-(2+alpha)*E/Epeak). No systematic residual
from the best fit model is seen in the spectral data of each instrument.
The best fit spectral parameters are: alpha = -0.89 (-0.28, +0.24) and
Epeak = 135 (-29, +66) keV (chi2/dof = 56/58).
The energy fluence and 16-ms peak flux in the 15-1000 keV band
are 1.45 (-0.31,+0.30) x 10^-6 erg/cm2 and (6.0 �� 2.7) x 10^-6 erg/cm2/s
respectively.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB120804_T03255/
All the quoted errors are at the 90% confidence level.
GCN Circular 13640
Subject
GRB120804A: Chandra observations and afterglow detection
Date
2012-08-14T12:30:14Z (13 years ago)
From
Eleonora Troja at GSFC <eleonora.troja@nasa.gov>
E. Troja (NASA/GSFC/UMCP), T. Sakamoto (NASA/GSFC/UMCB),
N. Gehrels (NASA/GSFC), D. Donato (NASA/GSFC/UMCP),
and J. L. Racusin (NASA/GSFC) report:
We observed the field of GRB 120804A (Lien et al., GCN Circ. 13573) with
the Chandra ACIS-S starting on August 13, 2012 10:52:08 UT (~9.4 d after
the GRB trigger) for a total exposure of 19.8 ks. Within the Swift/XRT
enhanced position (Osborne et al., GCN Circ. 13577) we clearly detect a
source at Ra, Dec = 233.94786, -28.7823 which is equivalent to:
RA (J2000) = 15h 35m 47.49s
Dec (J2000) = -28d 46' 56.3"
with an uncertainty of 0.6 arcsec (radius, sys+stat, 90% containment).
This position is consistent with the putative host galaxy S1
(Chornock et al., GCN Circ. 13586).
The X-ray afterglow is detected at a count rate of (1.6 +/- 0.3)E-03 cts/s
(0.5-8.0 keV). By using the spectral parameters derived from the Swift/XRT
observations (Stroh et al., GCN Circ. 13580) we estimate an observed X-ray
flux of (1.5 +/-0.3)E-14 erg/cm2/s in the 0.3-10 keV energy band.
Our measurement is consistent with the power-law decay of ~1.1 reported
by Stroh et al. (GCN Circ. 13580), and sets a lower limit to the jet-break
time of t_j>9 d.
We thank Harvey Tananbaum and the entire Chandra staff for approving and
rapidly executing this observation.
GCN Circular 13643
Subject
GRB 120804A: Possible temporal break in the X-ray light-curve
Date
2012-08-14T20:56:06Z (13 years ago)
From
Wen-fai Fong at CFA <wfong@cfa.harvard.edu>
R. Margutti, W. Fong, and E. Berger (Harvard) report:
"We analyzed the Swift-XRT and Chandra observations of the short GRB
120804A (Lien et al. GCN 13573; Troja et al., GCN 13640). Using the data at
t>10^4 sec, when the light curve appears less susceptible to variability,
we find moderate evidence for a temporal break with a pre-break index of
alpha1= 0.7 +\- 0.1, a post-break index of alpha2= 1.9 +\- 0.5, and a break
time of about 2x10^5 sec. The F-test indicates 5% probability of chance
improvement with respect to a single power-law fit. Plots are available
from:
https://www.cfa.harvard.edu/~rmargutt/flux_lightcurvefitBPL.pdf
https://www.cfa.harvard.edu/~rmargutt/flux_lightcurvefitSPL.pdf
Further X-ray observations are required to clarify the nature/presence of
the temporal break."
GCN Circular 13715
Subject
XMM observations of the short GRB120804A
Date
2012-09-05T19:53:38Z (13 years ago)
From
Raffaella Margutti at Harvard <raffaella.margutti@gmail.com>
R. Margutti (Harvard), V. Mangano (INAF IASF-Palermo), E. Berger, and W.
Fong (Harvard) report:
"We observed the short GRB120804A (GCN 13573) with XMM-Newton
starting on 2012 August 22, 21:51:29 UT (18.8 days after the burst).
GRB120804A is clearly detected at a level of 6 sigma with count-rate of
(4.3 +\- 0.7)e-3 cps (0.2-10 keV) in the pn. The pn net exposure time is
25.5 ks.
Using our best estimate of the intrinsic neutral hydrogen absorption
(NH_int=3.2e21 cm-2) and the Galactic absorption in the direction of the
burst (NH_gal=9.3e20 cm-2, Kalberla et al., 2005), this translates into
an unabsorbed 0.3-10 keV flux of 2.4e-14 erg/s/cm2. Our analysis
does not support the presence of a jet break for t< 18.8 days.
Combining the Swift-XRT (GCN 13580), Chandra (GCN 13640, 13643) and
XMM observations, for t>10^4 s the X-ray afterglow of GRB120804A is
best modeled by a simple power-law decay with index=1.0 +\- 0.1.
We thank the XMM-Newton staff for approving this observation."
GCN Circular 13841
Subject
GRB 120804A: Late-time Chandra observation
Date
2012-10-04T17:56:15Z (13 years ago)
From
David Burrows at PSU/Swift <dnburrows@gmail.com>
GRB 120804A: Late-time Chandra observation
David N. Burrows (PSU), Bin-Bin Zhang (PSU) and Eleonora Troja
(NASA/GSFC/UMCP) report:
We re-observed the field of GRB 120804A (Lien et al., GCN Circ. 13573)
with the Chandra ACIS instrument, starting on September 18, 2012
16:04:50 UT (~46 days after the GRB trigger), for a total exposure of
60 ks. The X-ray afterglow is clearly detected at the 10 sigma level.
The inferred flux is consistent with an extrapolation of
the earlier Swift XRT observations (Troja et al., GCN Circ. 13640) and the
XMM observation (Margutti et al. (GCN Circ. 13715), and shows a
continuing decline in flux with a power-law decay slope of ~1.0 and
no evidence for a jet break, consistent with Berger et al. (arXiv:1209:5423).
We thank Dan Schwartz and the entire Chandra staff for
rapidly executing this observation.