[vsnet-grb-info 2174] GRB 050822C: Swift detection of a bright burst

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4013
SUBJECT: GRB 050822C: Swift detection of a bright burst
DATE:    05/09/22 21:05:45 GMT
FROM:    Jay R. Cummings at NASA/GSFC/Swift  <jayc at milkyway.gsfc.nasa.gov>

J. Norris (GSFC), L. Barbier (GSFC), D. Burrows (PSU), A. Cucchiara (PSU),
J. Cummings (GSFC/NRC), N. Gehrels (GSFC), M. Goad (U. Leicester),
O. Godet (U. Leicester), S.T. Holland (GSFC/USRA), J. Kennea (PSU),
F. Marshall (GSFC), D. Palmer (LANL), T. Sakamoto (GSFC/NRC),
on behalf of the Swift team:

At 19:55:50 UT Swift-BAT triggered and located GRB 050922C (Trigger=156467)
and immediately slewed.  The BAT on-board calculated position is RA,Dec= 
317.391d, -8.772d {21h 09m 34s, -08d 46' 17"} (J2000) with an uncertainty
of 3 arcmin (radius, 90% containment, stat+sys).  The TDRSS light curve 
shows an intense GRB with a rising precursor starting at T-5 seconds, 
followed by 5-second long main peak surmounted by three spikes.  The third 
and most intense spike has a maximum count rate at T+1 sec of 15,000 
counts/sec (15-350 keV).

XRT began observing the field at 19:57:38 UT, 108 seconds after the BAT
trigger. XRT performed an onboard centroid and found a previously
uncataloged fading source in the field of view at the following coordinates:

RA(J2000):  21:09:33.4,
Dec(J2000): -8:45:30.5,

with an estimated uncertainty of 8 arcseconds radius (90% containment). This
position is 49 arcseconds from the BAT position and within 4.5 arcsec of the
optical transient reported by Rykoff et al. (GCN circ 4011 [mistitled]).

UVOT began observing at 111 sec after the trigger.  The small UVOT TDRSS 
image does not overlap the XRT error circle. However, the full-field UVOT 
source list contains a bright, uncataloged source within the XRT error
circle.  We estimate the V magnitude at 15.5 +- 0.5 uncorrected for 
extinction.  The V-band extinction in this field is A_V = 0.34 mag.