TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3407
SUBJECT: GRB 050509a: Swift-BAT refined analysis
DATE:    05/05/10 16:36:13 GMT
FROM:    Louis M Barbier at NASA/GSFC/Swift  <lmb@cosmicra.gsfc.nasa.gov>

L. Barbier (GSFC), S. Barthelmy (GSFC), P. Boyd (GSFC-UMBC),
J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), 
D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), 
T. Mitani (ISAS) D. Palmer (LANL), A. Parsons (GSFC), 
T. Sakamoto (GSFC/NRC), G. Sato (ISAS), M. Suzuki (Saitama), 
J. Tueller (GSFC), W. Voges (MPE)

on behalf of the Swift/BAT team:

At 01:46:28 UT Swift-BAT detected GRB 050509a (trigger=118707)
(GCN Circ 3379, C. Hurkett, et al.). The refined BAT ground position
is (RA,Dec) = 310.608,+54.059, [deg; J2000] {20:42:24; +54:00:14} 
+- 0.45 arcmin, (95% containment). XRT found an uncatalogued
x-ray source 13 arcseconds from the BAT position (GCN Circ 3380,
J. Kennea, et al.) The coding was 100% in the FOV.  

The 1-s maskweighted lightcurve shows two distinct peaks. T90 (15-350 keV) 
is (11.6 +- 1.0) seconds (estimated error including systematics).  

The photon index of the time-averaged spectrum is 2.1 +- 0.2.  
The fluence in the 15-350 keV band is (4.6 +- 0.7) x 10^-7 erg/cm2.  
The 1-s peak photon flux measured from T0+0.388 second in the 15-350 keV 
band is (0.98 +- 0.13) ph/cm2/s.  All the quoted errors are at the 90% 
confidence level.