[vsnet-grb-info 13768] GRB 130807A: Swift detection of a GRB or Galactic transient

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15082
SUBJECT: GRB 130807A: Swift detection of a GRB or Galactic transient
DATE:    13/08/07 10:50:03 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

A. Melandri (INAF-OAB), D. N. Burrows (PSU),
P. A. Evans (U Leicester), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU),
M. Stamatikos (OSU/NASA/GSFC) and R. L. C. Starling (U Leicester)
report on behalf of the Swift Team:

At 10:25:43 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130807A (trigger=565651).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 269.801, -27.613 which is 
   RA(J2000) = 17h 59m 12s
   Dec(J2000) = -27d 36' 44"
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 at least 30 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 10:27:08.2 UT, 85.0 seconds after
the BAT trigger. Although a bright and variable source is apparent 
in the promptly downloaded light curve, the instrument did not
centroid on the source in the initial 2.5-s promptly downloaded
image, and the XRT stayed in WT mode for the remainder of the 
short first snapshot until Swift slewed away from the target. 
We therefore will have to wait until the second orbit to 
localize the XRT counterpart. 

UVOT took a finding chart exposure of 166 seconds with the U filter starting
145 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. Because of the density of catalogued stars, further analysis
is required to report an upper limit for any afterglow in the sub-image. The
8'x8' region for the list of sources generated on-board covers 100% of the BAT
error circle. Because of the density of catalogued stars, further analysis is
required to report an upper limit for any afterglow in the region. No
correction has been made for the large, but uncertain extinction expected. 

Due to the proximity of this source to the Galactic center 
(3.3 degrees from the center) it is more likely that this is a 
Galactic source rather than a cosmological GRB.  Determination
of the nature of this source will require the full downlinked data. 

Burst Advocate for this burst is A. Melandri (andrea.melandri AT brera.inaf.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.)