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GCN Circular 4975

GRB 060418: Refined Analysis of the Swift-BAT burst
2006-04-18T15:17:40Z (18 years ago)
Louis M Barbier at NASA/GSFC/Swift <>
J. Cummings (GSFC/ORAU), L. Barbier (GSFC), S. Barthelmy (GSFC), 
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/ORAU), G. Sato (ISAS),
J. Tueller (GSFC),  on behalf of the Swift-BAT team:

Using the data set from T-119 to T+183 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 060418 (trigger #205851)
(Falcone, et al. GCN 4966).  The BAT ground-calculated position
is RA,Dec = 236.428, -3.642 deg {15h 45m 42.6s, -3d 38' 31.5"} (J2000)
+- 0.8 arcmin, (radius, sys+stat, 90% containment).  The partial coding was 30%.

The mask-weighted lightcurve shows three overlapping peaks - a slow rise
beginning at T-8 to a broad peak at T+10, a smaller peak at T+18, followed 
by the largest spike at T+27. There is a small bump in the lightcurve at 
T+130 which coincides with a flare seen in the XRT data.
(Falcone et al. GCN 4973). T90 (15-350 keV) is 52 +- 1 s.

The time-averaged spectrum from T-19.2 to T+136.6 is best fit by a 
simple power-law model. The power law index of the time-averaged spectrum 
is 1.66 +- 0.05. The fluence in the 15-150 keV band is 8.1 +- 0.2 x 10-06 
erg/cm2. The 1-sec peak photon flux measured from T+27.45 sec in the 
15-150 keV band is 6.7 +- 0.4 ph/cm2/sec.

Eiso is 5.3e+52 ergs in the 37.35 - 373.5 keV range at the GRB rest
frame using z = 1.49 (Dupree et al. GCN 4969, Vreeswijk et al. GCN 4974).

All the quoted errors are at the 90% confidence level.
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