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GCN Circular 9465

Subject

GRB 090531B: Swift-BAT refined analysis

Event

GRB 090531B

Date

2009-06-01T00:03:02Z (16 years ago)

From

Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>

T. N. Ukwatta (GWU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC)
(i.e. the Swift-BAT team):
 
Using the data set from T-61 to T+242 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090531B (trigger #353728)
(Cummings, et al., GCN Circ. 9461Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 252.070, -36.015 deg, which is 
   RA(J2000)  =  16h 48m 16.8s 
   Dec(J2000) = -36d 00' 53.4" 
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted light curve shows an initial bright spike with a total
width of 1.3 sec.  It returns to baseline and then starts (!T+15 sec)
a long smooth rise to a peak around T+40 sec and a smooth decline
ending at ~T+110 sec.  The spike is spectrally harder than the long smooth peak.
This lightcurve is consistance with a short hard burst with an extended emission.
T90 (15-350 keV) is 80 +- 23 sec (estimated error including systematics).
 
The time-averaged spectrum from T-13.0 to T+67.0 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.51 +- 0.22.  The fluence in the 15-150 keV band is 7.1 +- 0.9 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.2 sec in the 15-150 keV band
is 1.25 +- 0.1 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/353728/BA/