TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3289
SUBJECT: GRB 050418: Swift-BAT refined analysis
DATE:    05/04/18 15:30:54 GMT
FROM:    Takanori Sakamoto at NASA/GSFC  <takanori@milkyway.gsfc.nasa.gov>

T. Mitani (ISAS), L. Barbier (GSFC), 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), J. Tueller (GSFC), 
on behalf of the Swift/BAT team:

At 11:00:34.6 UT Swift-BAT detected GRB 050418 (trigger=114893)
(GCN Circ 3288, Barbier et al.).  The refined BAT ground position
is (RA,Dec) = 44.346, -18.538, [deg; J2000] +- 3 arcmin, (95%
containment).  The partial coding was 48 %.  

The BAT mask-weighted light curve shows an initial triangular peak
(~12 s rise, ~8 s fall time) followed by a quartet of softer peaks
from 50 to 80 seconds after the maximum of the first peak, with
the last and brightest of the four being as intense as the
initial peak in 15-50 keV, but less than a quarter the height
in 50-100 keV.  T90 (15-350 keV) is (83 +- 5) seconds 
(estimated error including systematics).  

The photon index of the time-averaged spectrum is 1.7 +- 0.1.  The 
fluence in the 15-350 keV band are (8.6 +- 0.4) x 10^-6 erg/cm2.  
The 1-s peak photon flux measured from T0+0.75 second in the 15-350 
band is (5.0 +- 0.3) ph/cm2/s.  All the quoted errors are at the 90% 
confidence level.