[vsnet-grb-info 6696] GRB 080928, Swift-BAT final refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8297
SUBJECT: GRB 080928, Swift-BAT final refined analysis
DATE:    08/09/29 12:41:32 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

E. Fenimore (LANL), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC),
J. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+494 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 080928 (trigger #326115)
(Sakamoto, et al., GCN Circ. 8292).  The BAT ground-calculated position is
RA, Dec = 95.061, -55.176 deg, which is 
   RA(J2000)  =  06h 20m 14.6s 
   Dec(J2000) = -55d 10' 34.8" 
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 84%.
 
With all the data downlinked, the mask-weighted light curve shows
that BAT triggered on a weak blip that occurred long before the
main emission of this burst.  The initial peak started at ~T-10 sec,
peaked at ~T_zero, and returned to baseline around T+30 sec.
Then a second, slightly larger peak, started at ~T+50 and ended at ~T+130 sec.
Then the main emission started at ~T+170, with a pair of peaks at ~T+205 and
~T+215 sec.  The emaission tails down to almost background at T+400 sec
at which time Swift started to enter the SAA and the errors on the flux
become large.  T90 (15-350 keV) is 280 +- 30 sec (estimated error
including systematics).
 
The time-averaged spectrum from T+51.1 to T+381.5 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.77 +- 0.12.  The fluence in the 15-150 keV band is 2.5 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+202.83 sec in the 15-150 keV band
is 2.1 +- 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/326115/BA/