TITLE:   GCN CIRCULAR
NUMBER:  34313
SUBJECT: GRB 230802A: Swift detection of a burst
DATE:    23/08/02 07:08:39 GMT
FROM:    K.L. Page at U Leicester <klp5@leicester.ac.uk>


N. J. Klingler (GSFC/UMBC/CRESSTII), V. D'Elia (SSDC & INAF-OAR),
P. A. Evans (U Leicester), J. A. Kennea (PSU), S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa), A. Melandri (INAF-OAR),
K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 06:50:26 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 230802A (trigger=1182085).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 76.221, +19.570 which is 
   RA(J2000) = 05h 04m 53s
   Dec(J2000) = +19d 34' 10"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a wide pulse
structure with a duration of about 60 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 06:51:30.3 UT, 64.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 76.23952, 19.56147
which is equivalent to:
   RA(J2000)  = 05h 04m 57.48s
   Dec(J2000) = +19d 33' 41.3"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 69 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 https://www.swift.ac.uk/sper. No
spectrum from the promptly downlinked event data is yet available to
determine the column density. 

The initial flux in the 2.5 s image was 1.25e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 73 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 expected extinction corresponding to E(B-V) of
0.614. 

Burst Advocate for this burst is N. J. Klingler (noelklin AT umbc.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/)