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GCN Circular 8708

Subject
GRB 081221, Swift-BAT refined analysis
Date
2008-12-22T19:27:08Z (15 years ago)
From
Jay R. Cummings at NASA/GSFC/Swift <jayc@milkyway.gsfc.nasa.gov>
J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
E. A. Hoversten (PSU), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD),
K. McLean (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)
(i.e. the Swift-BAT team):

Using the data set from T-239 to T+873 sec from the recent telemetry 
downlink,
we report further analysis of BAT GRB 081221 (trigger #337889)
(Hoversten, et al., GCN Circ.  8687).  The BAT ground-calculated 
position is
RA, Dec = 15.801, -24.542 deg which is
  RA(J2000)  =  01h 03m 12.2s
  Dec(J2000) = -24d 32' 32.8"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 61%.

The mask-weighted light curve shows two main overlapping peaks, the smaller
from about T+0 to T+12 sec and the larger from about T+12 to T+40 sec, with
multiple subsidiary peaks and an extended tail visible to about T+150 sec.
T90 (15-350 keV) is 34 +- 1 sec (estimated error including systematics).

The time-averaged spectrum from T-0.3 to T+112.6 sec is best fit by a power
law with an exponential cutoff.  This fit gives a photon index 1.21 +- 
0.13,
and Epeak of 69.9 +- 3.9 keV (chi squared 37.73 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.81 +- 0.03 x 10-05 
erg/cm2
and the 1-sec peak flux measured from T+21.42 sec in the 15-150 keV band is
18.2 +- 0.5 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.86 (chi squared 119.90 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/337889/BA/
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