TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3173
SUBJECT: GRB 050401 BAT refined analysis
DATE:    05/04/02 20:14:18 GMT
FROM:    Takanori Sakamoto at NASA/GSFC  <takanori@milkyway.gsfc.nasa.gov>

T. Sakamoto (GSFC/NRC), S. Barthelmy, L. Barbier (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), G. Sato (ISAS), 
M. Suzuki (Saitama), M. Tashiro (Saitama U.), J. Tueller (GSFC), 
on behalf of the Swift/BAT team: 
 
At 14:20:15 UT Swift-BAT detected GRB 050401 (trigger=113120) 
(GCN Circ 3162,  Barbier et al.). The refined BAT ground position is 
(RA,Dec) = 247.880, +2.191, [deg; J2000] +- 3 arcmin, (95% containment).  
This is 38 arcseconds from the XRT (GCN Circ 3161, Angelini et al.) and 
confirmed optical afterglow (GCN Circ 3163, McNaught et al.) positions. 
 
The burst had 4 distinct peaks. There were three initial peaks of roughly 
comparable intensity, at times T-6, T-1 and T+3.  These peaks all had 
durations of between 1 and 2 seconds.  These peaks were followed by 
a stronger peak beginning at T+23 and lasting ~6 seconds.  The total 
burst duration T90 is estimated at 33 seconds +/- 2 s 
(including systematics) 
 
The fluence derived from the event data is 1.4 X 10^-5 erg/cm^2 
in the 15-350 keV band.  The 1-s peak flux (T+24.6 s) is 14 ph/cm^2/s 
(also 15-350 keV).  The photon index of the 1-s peak spectrum 
(T+0 s) is 1.17 +/- 0.12 (90% confidence).  The time-averaged 
spectrum yields a photon index of 1.50 +/- 0.06 (90% confidence). 
Both the 1-s and time-averaged spectra are well fit by a simple power-law.