GCN Circular 8169

D. Grupe (PSU), W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),
M. M. Chester (PSU), J. R. Cummings (NASA/UMBC),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL), T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU)
report on behalf of the Swift Team:

At 01:12:23 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080903 (trigger=323542).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 86.797, +51.326 which is 
   RA(J2000) = 05h 47m 11s
   Dec(J2000) = +51d 19' 35"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty).  The BAT light curve showed a broad single-peaked
structure with a duration of about 50 sec.  The peak count rate
was 1250 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 01:13:21.8 UT, 58.5 seconds after
the BAT trigger. Using promptly downlinked data we find a bright, fading,
uncatalogued X-ray source located at RA, Dec 86.79071, 51.26363 which
is equivalent to:
   RA(J2000)  = 05h 47m 9.77s
   Dec(J2000) = +51d 15' 49.1"
with an uncertainty of 3.0 arcseconds (radius, 90% containment). This
location is 224 arcseconds from the BAT onboard position, outside the
on-board BAT error circle, but within the BAT ground-calculated error
circle. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
1.67e+21 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 1.80e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 400 seconds with the V filter
starting 75  seconds after the BAT trigger. No 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 3-sigma upper limit at the
location of the XRT candidate is 19.4 mag. No correction has  been
made for the expected extinction of about 0.7 magnitudes. 

Burst Advocate for this burst is D. Grupe (grupe AT astro.psu.edu). 
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.)