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GCN Circular 13828

Subject
GRB 120927A, Swift-BAT refined analysis
Date
2012-09-28T17:04:37Z (12 years ago)
From
Jay R. Cummings at NASA/GSFC/Swift <james.r.cummings@nasa.gov>
GRB 120927A, Swift-BAT refined analysis
  
D. M. Palmer (LANL), 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), A. Maselli (INAF-IASFPA),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC),
T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
  
Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 120927A (trigger #534815)
(Maselli, et al., GCN Circ. 13822Not found
 
 
).  The BAT ground-calculated position is
RA, Dec = 136.606, 0.420 deg which is
    RA(J2000)  =  09h 06m 25.3s
    Dec(J2000) = +00d 25' 13.5"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).  The
partial coding was 64%.
  
The mask-weighted light curve shows multiple overlapping peaks with an overall
FRED profile starting about T-15 seconds and significant until about
T+32 seconds.  T90 (15-350 keV) is 43 +- 18 sec (estimated error including
systematics).
  
The time-averaged spectrum from T-37.94 to T+41.04 sec is best fit by a power
lawwith an exponential cutoff.  This fit gives a photon index 0.63 +- 0.38,
and Epeak of 66.1 +- 9.6 keV (chi squared 50.98 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 2.6 +- 0.3 x 10^-06 erg/cm2
and the 1-sec peak flux measured from T-3.93 sec in the 15-150 keV band is
1.6 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.64 +- 0.08 (chi squared 77.30 for 57 d.o.f.).  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/534815/BA/