GRB 051012

G. Sato (ISAS), L. Barbier (GSFC), S. Barthelmy (GSFC),
J. Cummings (GSFC/NRC), N. Gehrels (GSFC), D. Hinshaw (GSFC-SPSYS),
H. Krimm (GSFC/USRA), K. McLean (LANL), C. Markwardt (GSFC/UMD),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC), J. Tueller (GSFC),
on behalf of the Swift-BAT team:


At 2005-10-12 17:05:58 UT, Swift-BAT triggered and detected GRB 051012
(trigger 159413).  Because Swift was executing a preplanned slew, the 
burst was not identified onboard and no prompt notices were distributed.
Using the data set from T-4 to T+16, the refined BAT ground position is 
RA, Dec 270.564d, -52.795d {18h 02m 15s, -52d 47' 40"} [deg; J2000], 
+- 1.8 arcmin (radius, sys+stat, 90% containment). The burst was in the
fully-coded field of view.

The lightcurve shows a single weak peak with a slow rise and fall from
approximately T-3 to T+11 sec.  T90 (15-350 keV) was 13 +- 1 sec (estimated 
error including systematics).  Because of the slew, we cannot rule out 
further emission after T+16 sec.

The power law index of the time-averaged spectrum was 2.25 +- 0.25.  The
fluence in the 15-150 keV band was (2.9 +- 0.5) x 10^-7 ergs / cm^2.  The
1-sec peak flux measured from T+3 sec in the 15-150 keV band was
0.6 +- 0.2 photons / cm^2 sec. All the quoted errors are at the 90%
confidence level.

A.P. Beardmore, K.L Page (U. Leicester), D.N. Burrows (PSU), O. Godet (U.
Leicester), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), N. Gehrels
(GSFC), M. Chester (PSU) and R. Fink (GSFC) report on behalf of the
Swift-XRT team:

The XRT began observing the field of GRB051012 on 13 October 2005, 102.5
ks after the burst. Because Swift was executing a preplanned slew at the
time of the burst, the burst was not identified on-board, thus causing a
significant delay in follow-up observations (Sato et al., GCN 4093
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 ). Using
the first 19.1 ks of data, collected between 102.5 and 206.7 ks after the
burst, a faint uncatalogued source was detected, with a confidence level
of greater than 99.9%, at the following coordinates:

RA(J2000):   18h 02m 11.1s
Dec(J2000): -52d 47' 12.3"

This position uses the latest XRT boresight correction and has an
estimated uncertainty of 6.4" (90% containment); it is 46" from the BAT
ground position reported by Sato et al.

The count-rate of this source is (5.3 +/- 2.5)e-4 ct s^-1, giving an
estimated observed flux of 2.1e-14 erg cm^-2 s^-1 (0.3-10 keV), assuming a
Crab-like spectrum and the Galactic absorbing column of 9e20 cm-2. The
corresponding unabsorbed flux is 2.8e-14 erg cm^-2 s^-1.

Because the source was quite faint, we were not able immediately to
determine whether or not it was variable. Two additional long exposures
were required to determine whether this source was fading. A total of 50.3
ks of data, taken between 206.7 and 797.9 ks after the trigger (between
2005-10-15 and 2005-10-21), revealed no detection of the source, with a
3-sigma upper limit on the count-rate of 2.4e-4 ct s^-1 [corresponding
observed (unabsorbed) flux of 9.7e-15 (1.3e-14) erg cm^-2 s^-1]. Since the
source has almost certainly faded, it is likely to be the X-ray afterglow
of GRB051012.