GRB 120803A

J. L. Racusin (NASA/GSFC), W. H. Baumgartner (GSFC/UMBC),
A. P. Beardmore (U Leicester), P. A. Evans (U Leicester),
C. Guidorzi (U Ferrara), J. A. Kennea (PSU), K. L. Page (U Leicester),
D. M. Palmer (LANL) and T. Sakamoto (NASA/UMBC) report on behalf of
the Swift Team:

At 07:22:16 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120803A (trigger=529582).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 269.565, -6.715 which is 
   RA(J2000) = 17h 58m 16s
   Dec(J2000) = -06d 42' 53"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 30 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 07:24:43.1 UT, 147.0 seconds after
the BAT trigger. No source was detected in 1.0 ks of promptly
downlinked data, which covered 91% of the BAT error circle. We are
waiting for the full dataset to detect and localise the XRT
counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 149 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 25% of
the BAT 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
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
0.94. 

This event is of low significance (7.3 sigma) in the BAT trigger image,
and no XRT source has been found in the 91% of the BAT error circle
covered by the immediately-available data. It is unusual for a real 
long GRB to lack an XRT counterpart.  Therefore, we cannot confirm the 
reality of this event until we receive the complete downlinked data. 

Burst Advocate for this burst is J. L. Racusin (judith.racusin AT nasa.gov). 
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.)

T. N. Ukwatta (MSU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
J. L. Racusin (NASA/GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS),
M. Stamatikos (OSU), J. Tueller (GSFC)
(i.e. the Swift-BAT team):
 
Using the data set from T-61 to T+242 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 120803A (trigger #529582)
(Racusin, et al., GCN Circ. 13565
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 269.531, -6.733 deg, which is 
   RA(J2000)  =  17h 58m 07.4s 
   Dec(J2000) = -06d 43' 58.0" 
with an uncertainty of 2.5 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 54%.
 
The mask-weighted light curve shows a single peak starting at ~T+0,
peaking ~T+3 sec, and returning to baseline at ~T+20 sec.
T90 (15-350 keV) is 10.0 +- 3.6 sec (estimated error including systematics).
 
The time-averaged spectrum from T+0.40 to T+11.40 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
0.86 +- 0.35.  The fluence in the 15-150 keV band is 3.0 +- 0.5 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+3.40 sec in the 15-150 keV band
is 0.4 +- 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/529582/BA/

We note that in our original circular (13565) that this event was labeled
as a "possible" GRB.  Given that the BAT detection significance
in ground proccessing has risen to 8.0 sigma, that the lightcurve shape
is consistant with a GRB, and that it is off the Galactic Plane,
we are confident that this trigger is due to a real GRB.

P.A. Evans, K.L. Page (U. Leicester) and J.L. Racusin (NASA/GSFC) report
on behalf of the Swift-XRT team:

We have analysed 2.5 ks of Photon Counting mode XRT data on GRB 120803A
from 155 s to 5.8 ks after the BAT trigger (Racusin et al., GCN Circ
13565
Loading...
 
 ). We find a single, uncatalogued X-ray source at RA,Dec =
269.5140, -6.7628 which is equivalent to:

   RA(J2000)  = 17h  58m 03.36s
   Dec(J2000) = -06d 45' 46.2"

with an uncertainty of 4 arc sec (radius, 90% containment). This
source is  4.2 arcmin from the original BAT position (GCN Circ 13565
Loading...
 
 )
but only 2 arcmin from the refined BAT position (Ukwatta et al., GCN
Circ 13568
Loading...
 
 ), inside the refined BAT error circle.

The spectrum of this object can be modelled by an absorbed power-law
with a photon index of 1.1 (+0.9, -0.5). The absorption is consistent
with the Galactic value of 2.3e21 cm^-2 (Kalberla et al. 2005).

The source has a mean count-rate of 0.014 (+/- 0.0029) ct/sec, we cannot
tell at this time whether the source is fading. Further observations are
planned.

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

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 120803A (Racusin et al., GCNC 13565)
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 2012-08-03 14:07:49 UT (~6.8 h after the burst)
We did not find any new point source within the XRT circle
(Evans et al., GCNC 13569) 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
------------------------------------------------------
0.30747    14:45:01    3960.0   >19.7  >19.6  >18.8
------------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]

R. Usui, Y.Aoki, S. Kurita, T. Yoshii, M. Hayashi,
Y. Saito, Y. Yatsu, and N. Kawai (Tokyo Tech)  report
on behalf of the MITSuME collaboration:

The target name in the subject line of GCN13570
Loading...
 
  was not correct.
The true target is GRB 120803B (NOT GRB 120803A).
Please replace "GRB 120803A" with "GRB120803B".

The main text of the circular is correct.

P.A. Evans (U. Leicester) and J.L. Racusin (NASA/GSFC) report
on behalf of the Swift-XRT team:

The Swift-XRT re-observed GRB 120803A on 2012 August 10, for 4.1 ks,
starting 5.7 days after the BAT trigger (Racusin et al., GCN Circ.
13565
Loading...
 
 ). The X-ray source reported by Evans et al. (GCN Circ. 13569
Loading...
 
 ) is
no longer detected, to a 3-sigma upper limit of 3.4e-3 ct/sec,
significantly below the level it was seen at previously.

We therefore conclude that this source was the afterglow of GRB 120803A.

The results of the automated analysis for this burst are available at
http://www.swift.ac.uk/xrt_products/00529582/

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

L. Elenin (KIAM), A. Volnova (SAI MSU), I. Molotov (KIAM), A. Pozanenko 
(IKI) report on behalf of  larger GRB  follow-up collaboration:

We observed the field of  possible Swift GRB 120803A (Racusin  et al., GCN 
13565
Loading...
 
 ; Evans  et al., GCN 13615
Loading...
 
 ) with 0.45-m telescope of  ISON-NM 
observatory  starting on  Aug. 03 (UT) 07:24:37.  We took  several 
unfiltered images of 30 s  exposures.  Within XRT error circle (Evans et 
al., GCN 13569
Loading...
 
 ) we do not detect any new source. A  photometry of  co-added 
frames is based on the USNO-B1.0 (R2)  nearby  stars is following:

T_start,     T0+,           Exposure, UL(3 sigma),
(UT)          mid, d         (s)

07:24:37    0.00258      4x30         17.3
07:24:37    0.01486    45x30         18.0