[vsnet-grb-info 1827] GRB050724: Refined analysis of the Swift-BAT possible short burst

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3667
SUBJECT: GRB050724:  Refined analysis of the Swift-BAT possible short burst
DATE:    05/07/24 16:27:35 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <Scott at lheamail.gsfc.nasa.gov>

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

Using the full data set from the recent telemetry downlink, we report
further analysis of Swift-BAT Trigger #147478 (Covino, et al., GCN 3665).
The ground-analysis position is RA,Dec 246.177,-27.525 (J2000) with an
uncertainty of 3 arcmin (radius, 90%, stat+sys).  T90 is 3 +- 1 sec.
The lightcurve has an initial hard FRED peak at T+0.00 sec (FWHM of 0.256 sec)
and there is a smaller much softer peak at T+1.00 sec.  Fitting a simple
power law over the full interval from T-1.0 to T+3.0 seconds, the photon index
is 1.71 +/- 0.16 with a fluence of 6.3 +/- 1.0 X 10^-7 erg/cm^2.
The peak flux in a 1-sec wide window starting at T+0.04 seconds
is 3.9 +/- 0.3 ph/cm^2/sec.  All values are in the 15-350 keV band
at the 90% confidence level.

Given the second emission peak at T+1, the T90 of 3 sec, and
the power law index value of 1.71, we can not confirm, nor rule out,
that this burst falls into the short-burst category.  However, in the
energy range above 25 keV, the second, softer peak  and subsequent emission
is much less prominent, and so it is likely  that BATSE would have
classified this as a short GRB.