GRB 120803B

J. L. Racusin (NASA/GSFC), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), P. A. Evans (U Leicester),
C. Guidorzi (U Ferrara), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), O. M. Littlejohns (U Leicester) and
K. L. Page (U Leicester) report on behalf of the Swift Team:

At 11:06:06 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120803B (trigger=529606).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 314.224, +53.282 which is 
   RA(J2000) = 20h 56m 54s
   Dec(J2000) = +53d 16' 57"
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 30 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 11:07:22.4 UT, 75.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 314.23606, 53.30380 which is equivalent
to:
   RA(J2000)  = 20h 56m 56.65s
   Dec(J2000) = +53d 18' 13.7"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 82 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 5.67
x 10^21 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 149 seconds with the White filter
starting 78 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 3.5% 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
1.71. 

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.)

C. Guidorzi (U. Ferrara), C.G. Mundell, D. Bersier (LJMU),
N.R. Tanvir (U. Leicester) report on behalf of a larger
collaboration:

The 2-m Faulkes Telescope North automatically began observing
GRB 120803B (Racusin et al. GCN Circ. 13566
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 ) on August 03 2012,
11:09:06 UT corresponding to 180 seconds post burst trigger
with BVRi' filters. Within the XRT error circle, in the i-band
filter we found the following uncatalogued possibly fading source,

R.A. = 20:56:56.46
Dec = +53:18:14.4   (J2000)

with an uncertainty of about 1".
The detection is marginal, with an estimated magnitude of
19.5 +/- 0.5 in the i band at a mean time of 13.2 minutes
(100 s exposure) calibrated against nearby USNOB-1 stars.
The source is no longer visible in the latest frames.
In the R band we see nothing down to 21.4 mag at 32.5 minutes
post burst. The faintness and colour of the source might
partially be explained by the relatively large foreground
extinction, E(B-V)=1.7.

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:

We observed GRB 120803B ( Racusin et al., GCN Circular #13566
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 ) with the
optical three color (g, Rc, and Ic) CCD cameras attached to the MITSuME
50 cm telescope of Akeno Observatory, Yamanashi, Japan.

The observation started on 2012-08-03 11:07:28 UT ( ~ 82 sec after
the burst).  And we did not find any new point source
within the XRT error circle in the three bands.
The results of photometry (3sigma upper limits) are listed below.

The photon flux were calibrated against GSC2.3 catalog.

T0+[sec]      MID-UT     T-EXP[sec]       g'              Rc           Ic
-------------------------------------------------------------------------------------------
       82       11:09:51         240        > 18.0       > 18.0     > 17.3
      376       11:53:57        3600         >19.2
      376       11:53:32        3660                           >18.9
      376       11:53:02        3720
        >18.3
-------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst [sec]
T-EXP: Total Exposure time [sec]

[GCN OPS NOTE(04aug12): Per author's request, the "120803A" in the
Subject-line was changed to "120803B".]

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

Using 117 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 120803B, 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 = 314.23579, +53.30416 which is equivalent
to:

RA (J2000): 20h 56m 56.59s
Dec (J2000): +53d 18' 15.0"

with an uncertainty of 2.0 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.

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), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
 
Using the data set from T-60 to T+243 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 120803B (trigger #529606)
(Racusin, et al., GCN Circ. 12566
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 ).  The BAT ground-calculated position is
RA, Dec = 314.223, 53.298 deg, which is 
   RA(J2000)  =  20h 56m 53.6s 
   Dec(J2000) = +53d 17' 54.2" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 58%.
 
The mask-weighted light curve shows a FRED-like pulse starting at ~T-5 sec,
peaking at ~T+6 sec, and returning to baseline ~T+60 sec (or possibly T+90 sec).
T90 (15-350 keV) is 37.5 +- 7.9 sec (estimated error including systematics).
 
The time-averaged spectrum from T-2.67 to T+49.16 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.84 +- 0.36, 
and Epeak of 117.8 +- 77.4 keV (chi squared 53.7 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 2.5 +- 0.5 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+4.49 sec in the 15-150 keV band is
1.5 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.36 +- 0.08 (chi squared 60.5 for 57 d.o.f.).  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/529606/BA/

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 120803B (Racusin et al., GCNC 13566)
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 11:46:48 UT (~41 min after the burst)
We did not find any new point source within the XRT circle
(Goad et al., GCNC 13571) in all the three bands.
We also could not detect the previously reported afterglow (Guidorzi et al.,
GCNC 13567).

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
------------------------------------------------------
0.06994    12:46:50    6360.0   >20.5  >20.2  >18.9
------------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]

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

We have analysed 4.4 ks of XRT data for GRB 120803B (Racusin  et al.
GCN Circ. 13566
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 ), from 79 s to 17.5 ks after the  BAT trigger. The data
comprise 31 s in Windowed Timing (WT) mode with the remainder in Photon
Counting (PC) mode. The enhanced XRT position for this burst was given
by Goad et al. (GCN. Circ 13571).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.25 (+0.07, -0.06).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.2 (+/-0.4). The
best-fitting absorption column is  8.5 (+4.7, -2.8) x 10^21 cm^-2,
consistent with the Galactic value of 5.7 x 10^21 cm^-2 (Kalberla et
al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 8.4 x 10^-11 (1.1 x
10^-10) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     8.5 (+4.7, -2.8) x 10^21 cm^-2
Galactic foreground: 5.7 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.2 (+/-0.4)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00529606.

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