[vsnet-grb-info 7210] GRB 090107: Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8783
SUBJECT: GRB 090107: Swift-BAT refined analysis
DATE:    09/01/07 13:51:47 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

G. Sato (ISAS), 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), 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 090107 (trigger #339295)
(Ukwatta, et al., GCN Circ. 8782).  The BAT ground-calculated position is
RA, Dec = 302.409, 4.744 deg, which is 
   RA(J2000)  =  20h 09m 38.2s 
   Dec(J2000) = +04d 44' 37.9" 
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 74%.
 
The mask-weighted light curve shows two peaks.  The first is about 1.2 sec wide
and peaks at ~T+0.9 sec.  The second is about 6 sec wide and peaks at ~T+11 sec.
Because of the Sun observing constraint and because of a regular pre-planned 
target slew, the BAT has no data on this event past T+260 sec, until the next orbit.
T90 (15-350 keV) is 12.2 +- 0.7 sec (estimated error including systematics).
 
The time-averaged spectrum from T+0.2 to T+12.9 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.69 +- 0.27.  The fluence in the 15-150 keV band is 2.3 +- 0.5 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.30 sec in the 15-150 keV band
is 1.1 +- 0.2 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/339295/BA/