[vsnet-grb-info 5023] GRB 070809, Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6732
SUBJECT: GRB 070809, Swift-BAT refined analysis
DATE:    07/08/10 01:46:26 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

H. Krimm (GSFC/USRA), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
C. Markwardt (GSFC/UMD), F. E. Marshall (NASA/GSFC), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-120 to T+183 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 070809 (trigger #287344)
(Marshall, et al., GCN Circ. 6728).  The BAT ground-calculated position is
RA, Dec = 203.767, -22.119 deg  which is 
   RA(J2000)  =  13h 35m 4.2s 
   Dec(J2000) = -22d 7' 7" 
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 74%.
 
The mask-weighted light curve consists of a single peak starting at ~T-0.3
and ending at ~T+1.2 sec.  T90 (15-350 keV) is 1.3 +- 0.1 sec (estimated error
including systematics).
 
The time-averaged spectrum from T-0.4 to T+1.1 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.69 +- 0.22.  The fluence in the 15-150 keV band is 1.0 +- 0.1 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.08 sec in the 15-150 keV band
is 1.2 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.  We note that the T90-hardness_ratio for this burst falls in between
the SHB and LSB clusters in the T90-HR scatter plot for Swift-BAT.