GRB051109: Swift detection of a burst

TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 4213
SUBJECT: GRB051109: Swift detection of a burst
DATE: 05/11/09 02:14:42 GMT
FROM: David Palmer at LANL dmpalmer@mac.com

G. Tagliaferri (INAF-OAB), S. Barthelmy (GSFC), D. Burrows (PSU), M. Chester (PSU), N. Gehrels (GSFC), J. Hill (GSFC/USRA), S. T. Holland (GSFC/USRA), J. Kennea (PSU), F. Marshall (GSFC), T. Mineo (INAF-IASFPA), D. Palmer (LANL), T. Sakamoto (GSFC), on behalf of the Swift team:

At 01:12:20 UT, Swift-BAT triggered and located GRB051109 (trigger=163136).

The spacecraft slewed immediately. The BAT on-board calculated location is RA,Dec= 330.296d, +40.837d {22h 01m 11s, +40d 50′ 15″} (J2000), with an uncertainty of 3 arcmin (radius, 90% containment, stat+sys). The BAT light curve showed a multi-peak structure with a total duration of at least 25 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~2 seconds after the trigger.

The XRT began observing at 01:14:20 UT, 120 seconds after the BAT trigger. The XRT on-board software located a bright, previously uncatalogued, fading point source in the field at the following location:

RA(J2000): 22:01:15.5,
Dec(J2000): +40:49:21.7,

with an estimated uncertainty of 5.8 arcseconds (90% containment). This position lies 74 arcseconds from the BAT position reported above, and 2.8 arcseconds from the ROTSE position (Rykoff et al., GCN 4211). The initial flux estimate of this source is 1.1 x 10^-9 erg/s/cm^2.

The UVOT began observing at 01:14:23, 123 seconds after the BAT trigger. A bright, uncataloged source is apparent at RA,dec=330.3136,+40.8231 {22h01m15.26s, +40o49’23.2″} (J2000), coincident with the position of the ROTSE detection. The V-band magnitude is approximately 17; this magnitude is based on an on-board source detection algorithm and a more accurate brightness will be available following analysis of the full data set. V-band extinction in the direction of the UVOT position is A_V = 0.63.