TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3385
SUBJECT: GRB 050509b: Swift-BAT refined analysis of the short hard burst
DATE:    05/05/09 07:06:49 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <Scott@lheamail.gsfc.nasa.gov>

S. Barthelmy (GSFC),  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), T. Sakamoto (GSFC/NRC), G. Sato (ISAS),
M. Suzuki (Saitama), J. Tueller (GSFC), T. Mitani (ISAS),
F. Marshall (GSFC), T. Takahashi (ISAS)
on behalf of the Swift/BAT team:

At 04:00:19.23 UT Swift-BAT detected GRB 050509b (trigger=118749)
(GCN Circ 3381, C. Hurkett et al.).  The refined BAT ground position
is (RA,Dec) = 189.073,+28.991 {12:36:18,28:59:28} +- 2.8 arcmin [deg; J2000],
(95% containment).  This is 59 arcsec from the XRT position (Kennea et al.,
GNC 3383).  The burst was in the fully-coded FOV.  Using the event-by-event
data, the lightcurve shows a single spike with a duration of ~30msec.
Further, the hardness ratio S(50-100)/S(25-50) of ~1.5 puts this burst cleanly
in the short-hard cluster on the hardness_ratio vs duration scatter-plot.
 
Using a simple power-law model, the photon index of the time-averaged
spectrum is 1.5 +- 0.4.  The fluence in the 15-350 keV band is
(2.3 +- 0.9) x 10^-8 erg/cm2.  The 1-s peak photon flux 
in the 15-350 band is (1.57 +- 0.36) ph/cm2/s.
All the quoted errors are at the 90% confidence level. 

We note that location is consistant with the galaxy cluster NSC J123610+285901
which has a redshift of z=0.22, which roughly translates to a distance 
of ~1 Gpc.  We also note that at this distance and the observed flux,
this is is an order of magnitude farther than the 27-Dec-04 SuperFlare
event from SGR1806-20 could be seen.