GRB 060111B: Swift detection of a burst

TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 4487
SUBJECT: GRB 060111B: Swift detection of a burst
DATE: 06/01/11 20:53:53 GMT
FROM: Scott Barthelmy at NASA/GSFC Scott@lheamail.gsfc.nasa.gov

M. Perri (ASDC), S. Barthelmy (GSFC), P. Boyd (GSFC), D. Burrows (PSU), J. Cummings (GSFC/NRC), N. Gehrels (GSFC), C. Gronwall (PSU), J. Kennea (PSU), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), F. Marshall (GSFC), D. Palmer (LANL), T. Sakamoto (GSFC) on behalf of the Swift team:

At 20:15:43 UT, Swift-BAT triggered and located GRB 060111B (trigger=176918). The spacecraft slewed immediately. The BAT on-board calculated location is RA,Dec 286.337d,+70.360d {19h 05m 21s,+70d 21′ 35″} (J2000), with an uncertainty of 3 arcmin (radius, 90% containment, stat+sys). The BAT light curve shows a main peak with a total duration of at least 25 sec. There is a possible second peak at T+55 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~2 seconds after the trigger.

XRT began observing the field at 20:17:02 UT, 79 seconds after the BAT trigger. On-board centroiding found a previously uncatalogued fading X-ray source in the field of view at the following coordinates:

RA(J2000) = 19 05 42.3

Dec(J2000)= 70 22 37

This location is 124 arcseconds from the BAT position. The estimated uncertainty is 8 arcseconds (90% confidence radius), including a systematic error of about 5 arcseconds due to an XRT boresight offset not currently corrected on-board. The initial flux was 1.7e-09 ergs/cm2/s (0.2-10 keV).

UVOT took a finding chart exposure of 200 seconds with the B filter starting 84 seconds after the BAT trigger. There is a candidate afterglow in the list of sources generated on-board at (RA,DEC) (J2000) of (286.4270,70.3760) or (19h 05m 42.48s,+70d 22′ 33.6″) with a 1-sigma error radius of about 0.5 arc sec. This position is 3.6 arc sec. from the center of the XRT error circle. The estimated V magnitude is 17.2 with a 1-sigma error of about 0.5 mag. No correction has been made for the expected visual extinction of about 0.4 magnitudes. This source was detected in a 200 sec B finding chart image taken beginning at 20:20:34 UT with a B magnitude of 19.55. We did not receive the V finding chart through TDRSS, so are unable to confirm the V magnitude from the V parameterized source list.