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TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4345
SUBJECT: GRB 051213: Swift-BAT detection of a burst
DATE:    05/12/13 08:09:13 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <Scott@lheamail.gsfc.nasa.gov>

T. Mineo (IASF-Pa INAF), S. Barthelmy (GSFC), G. Cusumano (IASF-Pa INAF),
N. Gehrels (GSFC), S. Hunsberger (PSU), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), K. Page (U Leicester), D. Palmer (LANL)
on behalf of the Swift team:

At 07:13:04 UT, Swift-BAT triggered and located GRB 051213 (trigger=172516).
The BAT on-board calculated location is RA,Dec 252.123d,-59.207d
{16h 48m 29s,-59d 12' 25"} (J2000), with an uncertainty of 3 arcmin
(radius, 90% containment, stat+sys).  The spacecraft did not slew
because of the Sun observing constraint.  The location is 36 deg from the Sun,
and it will not be observable by Swift NFIs for at least three weeks.
This was a 64-sec image trigger with a 9-sigma significance in the image domain.
The BAT lightcurve shows hints of emission, but it is not possible
to separate source variations from background variations in the rate domain.
The full data set from the next Malindi downlinks in a few hours
will allow the separation of source from background.

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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@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.