GRB 051016B: Swift detection of a soft burst

TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 4103
SUBJECT: GRB 051016B: Swift detection of a soft burst
DATE: 05/10/16 19:18:13 GMT
FROM: Scott Barthelmy at NASA/GSFC Scott@lheamail.gsfc.nasa.gov

A. Parsons (GSFC), S. Barthelmy (GSFC), A. Beardmore (U. Leicester), P. Boyd (GSFC), D. Burrows (PSU), J. Cummings (GSFC/NRC), N. Gehrels (GSFC), O. Godet (U. Leicester), C. Gronwall (PSU), J. Kennea (PSU), H. Krimm (GSFC/USRA), F. Marshall (GSFC), D. Palmer (LANL), T. Sakamoto (GSFC) on behalf of the Swift team:

At 18:28:09 UT, Swift-BAT triggered and located GRB 051016B (trigger=159994). The BAT on-board calculated location is RA,Dec 132.067d,+13.658d {08h 48m 16s,+13d 39′ 27″} (J2000), with an uncertainty of 3 arcmin (radius, 90% containment, stat+sys). The BAT light curve shows a double peak structure with a total duration of at least 15 sec — the slew started at T+15 sec, so determination of the full duration will have to wait until after the full data set is downlinked. The peak count rate was ~2200 counts/sec (15-150 keV), at ~1 and 3 seconds after the trigger. Initial inspection of the 4-channel lightcurves shows this burst to be soft.

The spacecraft slewed promptly and the XRT began observing the GRB at 18:29:24 UT, 75 sec after the BAT trigger. An uncatalogued source was found by the on-board centroiding algorithm at RA(J2000)=08h 48m 27.6s Dec(J2000)=+13d 39′ 25.5″ with an uncertainty of 8 arcsec radius (90% containment). This position lies 168 arcsec from the center of the BAT error circle. The initial flux is approximately 4.6e-10 ergs/cm2/s. The count rate decreases during the first 100 seconds.

UVOT began observing the field at 18:29:26 UT, 77 sec after the BAT trigger. The small image contains the entire XRT error circle. This image contains no new sources down to a limiting magnitude of 18.7 (3-sigma). No new source was seen in the list of sources from the entire UVOT field of view. E(B-V) in the direction of the XRT position is 0.037.