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GCN Circular 3251

Subject
GRB 050412: Swift-BAT refined analysis
Date
2005-04-12T16:38:05Z (19 years ago)
From
Scott Barthelmy at NASA/GSFC <Scott@lheamail.gsfc.nasa.gov>
J. Tueller, L. Barbier, S. Barthelmy (GSFC), J. Cummings (GSFC/NRC),
E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC),
G. Sato (ISAS), M. Suzuki (Saitama), M. Tashiro (Saitama U.)
on behalf of the Swift/BAT team:

At 05:44:03  UT Swift-BAT detected GRB 050412 (trigger=114485)
(GCN Circ 3237, Cummings et al.).  The refined BAT ground position
is (RA,Dec) = 181.089,  -1.206, [deg; J2000] +- 3 arcmin, (95%
containment).  This is 1.0 arc minutes from the position determined
by the XRT (GCN Circ 3241, Tamburelli et al.) and the LCO (GCN Circ
3244, Fox et al.)

Examination of the mask weighted light curve shows a 16-second main
peak, starting ~8 seconds before the trigger and having a roughly
symmetrical shape.  This is followed by smaller secondary peaks
lasting until ~24 seconds after the trigger.  The estimated T90
(15-350 keV) is 26 seconds +/- 2 secs (estimated error including
systematics).

Analysis of the event data shows that this is a very hard burst with
significant emission throughout the BAT energy range (15-350 keV).
The time-averaged total spectrum is consistent with a simple power-law,
with a photon index of  -0.62 +/- 0.18 (90% confidence).  However,
there may be significant systematic uncertainties with such a
hard spectrum.  The photon index of the 5-s peak spectrum (starting at
T0-0.784 s) (also simple power-law) is -0.47 +/- 0.23 (90% confidence).
The fluence derived from the event data is 2.1 (+/- 0.5) X 10^-6 erg/cm^2
in the 15-350 keV band and 9.6 (+/- 1.1) X 10^-7 erg/cm^2 in the
15-200 keV band.  The 5-s peak flux is 0.7 +/- 0.1 ph/cm^2/s (15-350 keV).
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