[vsnet-grb-info 12358] GRB 120909A: Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13733
SUBJECT: GRB 120909A: Swift-BAT refined analysis
DATE:    12/09/09 15:03:07 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

T. N. Ukwatta (MSU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
S. Immler (CRESST/GSFC/UMD), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS),
M. Stamatikos (OSU), J. Tueller (GSFC)
(i.e. the Swift-BAT team):
 
Using the data set from T-41 to T+556 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 120909A (trigger #533060)
(Immler, et al., GCN Circ. 13727).  The BAT ground-calculated position is
RA, Dec = 275.735, -59.432 deg which is 
   RA(J2000)  =  18h 22m 56.5s 
   Dec(J2000) = -59d 25' 55.2" 
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 48%.
 
The mask-weighted light curve shows multiple overlapping peaks. The burst was
already occurring when Swift-BAT came out of the SAA at ~T-40 sec.
The observed peaks occurred at ~T-38, ~T+1, ~T+28, and ~T+48 sec.
The burst returned to baseline at ~T+200 sec.  There is a possible peak
at ~T+490 to ~T+580 sec, at which point Swift had to slew due to an observing
constraint and the location went out of the BAT FoV.
 
The time-averaged spectrum from T-38.98 to T+95.17 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.39 +- 0.06.  The fluence in the 15-150 keV band is 6.8 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+0.88 sec in the 15-150 keV band
is 1.8 +- 0.3 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/533060/BA/