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GCN Circular 8923

Subject
GRB 090301A: Swift-BAT refined analysis
Date
2009-03-01T17:22:50Z (15 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
E. E. Fenimore (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), A. M. Parsons (GSFC),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. N. Ukwatta (GWU), L. Vetere (PSU)
(i.e. the Swift-BAT team):
 
Using the data set from T-61 to T+242 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090301A (trigger #344582)
(Vetere, et al., GCN Circ. 8920).  The BAT ground-calculated position is
RA, Dec = 338.142, 26.639 deg, which is 
   RA(J2000)  =  22h 32m 34.2s 
   Dec(J2000) = +26d 38' 19.0" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 35%.
 
The mask-weighted light curve shows a complex of overlapping and separated
peaks starting at ~T-20 sec and ending some time after T+86 sec
at which time the burst location went ouf out the BAT FOV when Swift slewed
to the next planned target.  Given that the burst location will not come out
of the Sun observing consrtaint until after April 15,  we will not have 
any further data on this burst.  T90 (15-350 keV) is 41.0 +- 2.2 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-17.0 to T+72.2 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.08 +- 0.12, 
and Epeak of 343.3 +- 328.8 keV (chi squared 37.39 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 2.3 +- 0.03 x 10^-5 erg/cm2
and the 1-sec peak flux measured from T+23.07 sec in the 15-150 keV band is
18.7 +- 0.6 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.25 +- 0.03 (chi squared 43.70 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/344582/BA/
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