GRB 110807A

V. D'Elia (ASDC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
M. M. Chester (PSU), C. Guidorzi (U Ferrara),
S. T. Holland (CRESST/USRA/GSFC), N. P. M. Kuin (UCL-MSSL),
C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC),
A. Melandri (INAF-OAB), D. M. Palmer (LANL), C. J. Saxton (UCL-MSSL),
G. Stratta (ASDC), C. A. Swenson (PSU) and T. N. Ukwatta (MSU) report
on behalf of the Swift Team:

At 19:57:46 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 110807A (trigger=458907).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 278.696, -8.760 which is 
   RA(J2000)  =  18h 34m 47s
   Dec(J2000) = -08d 45' 35"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single timebin spike
structure with a duration of less than 0.064 sec.  The peak count rate
was ~3500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 20:03:13.2 UT, 326.8 seconds after
the BAT trigger. Using promptly downlinked data we find an X-ray source
located at RA, Dec 278.71751, -8.76597 which is equivalent to:
   RA(J2000)  = 18h 34m 52.20s
   Dec(J2000) = -08d 45' 57.5"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 79 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. This
position is 6.6 arcseconds from that of a known X-ray source: 2XMM
J183452.4-084603 in the XMM-NEWTON XMMSSC catalogue. 

A power-law fit to a spectrum formed from promptly downlinked event
data does not constrain the column density. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 332 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 large, but uncertain extinction expected. 

Due to the short, soft nature of the burst, and the proximity
of the source to the Galactic plane (0.3 degrees) we suggest
that this source may be a previously unknown Soft Gamma Repeater. 
Verification of this could come if a second burst is seen or
the XRT counterpart shows periodicity. 

Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.it). 
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.)

A. S. Moskvitin, V. V. Sokolov and R. I. Uklein,
report on behalf of the SAO RAS GRB follow-up team:

We observed the field of GRB 110807A (D'Elia et al, GCN 12253
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 )
with the 6-meter BTA + Scorpio on August 7.843 -- 7.857 UT
(observations were started since 16 minutes after the BAT trigger).

We obtained 21 x 30 sec. exposures in Rc band. At our stacked image
(seeing = 1".9), inside the XRT error circle we clearly detected
only one object with the following coordinates:
R. A. = 18:34:52.42
Dec. = -08:45:57.08,
with approximately error 1" (all coordinates for Epoch = 2000).

The brightness of the object were measured as R = 23.44 +/- 0.34
(no extinction correction were made). Calibration were done against
the magnitude R2 = 17.85 of the USNO-B.1 star 0812-0420010
(R.A. = 18:34:51.24, Dec. = -08:45:40.1).

We also noted presence of the other object just outside from the XRT
error circle to the North-West which is marked as USNO-B.1 star
0812-0420027 (R.A. = 18:34:51.86, Dec. = -08:45:52.3).
At our image this object is extended along the South-East direction
and probably may be two or more objects.

Zoomed image from BTA can be found at
ftp://ftp.sao.ru/pub/grb/GRB110807A/GRB110807A_BTA.jpeg

The message may be cited.

A.J. Levan (U. Warwick), N.R. Tanvir (U. Leicester) report:

"The region around the newly discovered SGR 1834.9-0846 (D'Elia et
al. GCN 12253
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 ; Barthelmy et al. GCN 12259
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 ) has been imaged as part
of the UKIDSS Galactic Plane Survey (Lucas et al. 2008 MNRAS 391
136) in the J, H and K-bands on May 10, 2007. Close to the refined
XRT location (current 90% error radius 1.8") we find two sources.
One at:

RA(J2000) 18:34:52.17 
DEC(J2000) -08:45:54.0

which is also in 2MASS, and has catalogue magnitudes of J=16.41 +/-
0.01, H=14.96 +/- 0.01, K= 14.13 +/- 0.01. We however note that
this source appears marginally extended in the K-band imaging, and
may be the result of the superposition of two sources within this
crowded region.

The second source is at location:

RA(J2000) 18:34:52.02 
DEC(J2000) -08:45:54.5

and has magnitudes of J=17.73 +/- 0.03, H=16.67 /- 0.02, K=16.07+/-
0.04. There are also numerous faint sources at larger offsets from
the refined XRT position. Further observations will be needed to
ascertain if any of these sources exhibit photometric variability."

J. C. Tello, A. Sota and A. J. Castro-Tirado (IAA-CSIC Granada), on behalf
of a larger collaboration, report:

"We observed SGR 1834.9-0846/ GRB 110807A detected by Swift/BAT (D'Elia et
al., GCNC 12253, Barthelmy, GCN 12259
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 ) with the OSN 1.5m telescope. I-band
frames were obtained on 7 Aug, starting 16 min after the gamma-ray detection
(i.e. simultaneously to the BTA Rc-band observations, Moskvitin et al., GCNC
12254). Neither on the single I-band images (10s exposure time each) nor on
the co-added frames, taken between 20:14 and 21:48 UT, with total exposure
4820 sec, an object is detected within the Swift/XRT error box. The limiting
magnitude for the combined image is I = 21.6 (calibrated against USNO
B1.0)."

This message may be cited.