GRB 050922C: Swift detection of a bright burst

TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 4013
SUBJECT: GRB 050922C: Swift detection of a bright burst
DATE: 05/09/22 21:05:45 GMT
FROM: Jay R. Cummings at NASA/GSFC/Swift jayc@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.

[GCN OPS NOTE(22sep05): Per author’s request, the Subject-line was changed from “050822” to “050922”.]