GCN Circular 9724
Subject
GRB 090727: Swift-BAT refined analysis
Date
2009-07-28T12:00:35Z (15 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
C. B. Markwardt (GSFC/UMD), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), P. A. Evans (U Leicester), E. E. Fenimore (LANL),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), D. M. Palmer (LANL),
A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
Using the data set from T-240 to T+962 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 090727 (trigger #358520)
(Evans, et al., GCN Circ. 9718). The BAT ground-calculated position is
RA, Dec = 315.917, 64.937 deg, which is
RA(J2000) = 21h 03m 40.0s
Dec(J2000) = +64d 56' 12.7"
with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 83%.
The mask-weighted light curve shows an initial FRED-like peak starting at
~T-5 sec, peaking at ~T_zero, and ending at ~T+20 sec. The second, weaker,
peak starts at ~T+130 to ~T+150 sec. The third peak starts at ~T+180 sec,
peaks at ~T+270 sec, and ends at ~T+320 sec. This third peak corresponds
to the flare mentioned in Circ 9723 (Evans). T90 (15-350 keV) is 302 +- 23 sec
(estimated error including systematics).
The time-averaged spectrum from T-1.3 to T+318.9 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.24 +- 0.24. The fluence in the 15-150 keV band is 1.4 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+0.12 sec in the 15-150 keV band
is 0.5 +- 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/358520/BA/