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
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.