GCN Circular 3273

T. Sakamoto (GSFC/NRC), 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), G. Sato (ISAS), 
M. Suzuki (Saitama), M. Tashiro (Saitama U.), J. Tueller (GSFC), 
on behalf of the Swift/BAT team:

At 11:04:44.5  UT Swift-BAT detected GRB 050416 (trigger=114753)
(GCN Circ 3264, Sakamoto et al.).  The refined BAT ground position
is (RA,Dec) = 188.490,  21.053, [deg; J2000] +- 3 arcmin, (95%
containment).  This is 0.7 arc minutes from the position determined
by the XRT (GCN Circ 3268, Kennea, et al.).

The BAT mask weighted light curve shows a single peak of about one 
second duration followed by a small bump.  Most of the emission is 
in the 15-50 keV band.  T90 (15-350 keV) is (2.4 +- 0.2) seconds 
(estimated error including systematics).

The photon index of the spectrum is 2.9 +- 0.2.  The fluences in 
the 15-50 keV band and in the 15-350 keV band are 
(2.8 +- 0.2) x 10^-7 erg/cm2 and (3.8 +- 0.4) x 10^-7 erg/cm2 respectively.  
The peak photon fluxes in the 15-50 keV band and in the 15-350 band are 
(4.4 + 0.8) ph/cm2/s and (4.8 +- 0.6) ph/cm2/s respectively.  All the 
quoted errors are in 90% confidence level. 

The BAT team cautions that while there appears to be a deficit of 
counts below 20 keV, this is likely due to systematic errors in the 
response matrix being accentuated by the steep spectrum.