[vsnet-grb-info 2511] GRB 051213: Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4348
SUBJECT: GRB 051213: Swift-BAT refined analysis
DATE:    05/12/13 18:34:00 GMT
FROM:    Hans Krimm at NASA-GSFC  <krimm at milkyway.gsfc.nasa.gov>

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

Using the data set from T-75 to T+300 sec from the recent telemetry
downlink, we report on further analysis of GRB 051213
(trigger #172516)  (Mineo, et al., GCN 4345). The BAT
ground-calculated position is (RA,Dec) = 252.078, -59.229
{16h 48m 18.6s, -59d 13' 42.7"} [deg; J2000] +-1.8 arcmin,
(radius, sys+stat, 90% containment).  The partial coding was 68%.

The mask-weighted light curve shows a double-peaked structure, with each
episode lasting ~30 seconds and showing a roughly time-symmetrical structure.
The first episode peaks at T-7 sec, and the second at T+49 sec and emission
returns to background levels between the two episodes.   T90 (15-350 keV)
is (70 +- 5) sec (estimated error including systematics).

The power law index of the time-averaged spectrum is 1.64 +- 0.20.
The fluence in the 15-150 keV band is (8.0 +- 1.0) x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+48.9 sec in the 15-150 keV
band is (0.51 +- 0.14) ph/cm2/sec.  All the quoted errors are at the 90%
confidence level.

We are classifying this event as GRB, but given the soft spectrum and
long duration, we can not rule out that it is a hard x-ray transient.