GCN Circular 3654

GRB050721A: Swift-BAT detection of a weak burst

L.A. Antonelli (INAF/OAR), K. Page (U. Leicester), D. Morris (PSU), P. 
Romano (INAF/OAB), N. Gehrels (GSFC), P. Roming (PSU), P. Schady 
(MSSL), G. Tagliaferri (INAF/OAB) S. Barthelmy (GSFC), H. Krimm 
(GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), on behalf of 
the Swift team:

At 04:29:14.28 UT, Swift-BAT triggered and located GRB050721 
(trigger=146970). The spacecraft slewed immediately. The BAT on-board 
calculated location is RA, Dec 253.445d,-28.390d {+16h 53m 47s,-28d 23' 
22"} (J2000), with an uncertainty of 3 arcmin (radius, 90% containment, 
stat+sys). The BAT light curve shows a peak with a total duration of 
~10 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~5 
seconds after the trigger.

The XRT started the observation at 04:32:20 UT with XRT in automatic 
state, 186 sec after the BAT Trigger. An uncatalogued X-ray source was 
detected at the following position RA, Dec 16h 53m 44.7s, -28d 22' 
53''.3 with an uncertainty of about 6 arcsec (90% containment). This is 
42 arcsec from the BAT position reported above.

Based on the UVOT finding chart there is no new source at the XRT 
position.