GCN Circular 8051

W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
M. M. Chester (PSU), C. B. Markwardt (CRESST/GSFC/UMD),
D. M. Palmer (LANL) and E. Troja (INAF-IASFPA) report on behalf of
the Swift Team:

At 15:12:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080802 (trigger=318832).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 270.748, -32.333 which is 
   RA(J2000) = 18h 02m 60s
   Dec(J2000) = -32d 19' 59"
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 50 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 15:13:39.7 UT, 78 seconds
after the BAT trigger. Using promptly downlinked data we find a bright,
variable, uncatalogued X-ray source located at RA, Dec 270.72692,
-32.33395 which is equivalent to:
   RA(J2000)  = 18h 02m 54.46s
   Dec(J2000) = -32d 20' 02.2"
with an uncertainty of 3.1 arcseconds (radius, 90% containment). This is
1.1 arcminutes from the BAT position and within its error radius. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (2.75e+21
cm^-2, Kalberla et al. 2005), with an excess column of 2.3
(+2.63/-2.21) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 1.47e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 100 seconds with the White 
(160-650 nm) filter starting 86 seconds after the BAT trigger. No 
afterglow candidate is apparent in the initial data products. The 
2.7'x2.7' sub-image covers 25% of  the BAT error circle and 100% of 
the XRT error circle. The typical 3-sigma upper limit has been about 
 18.5 mag. The list of sources is typically complete to about 18 mag. 
 No  correction has been made for the expected extinction, which at
this location is large and uncertain. 

Because this source is near the Galactic center, this event may
be a local transient rather than a cosmological GRB.  However,
no known sources are found at the XRT position in either 
SIMBAD or NED. 

No BAT_POSITION notice was available due to a TDRSS hand-over
at the time of the burst.