TITLE:   GCN CIRCULAR
NUMBER:  40456
SUBJECT: GRB 250509A: Swift-BAT refined analysis
DATE:    25/05/14 02:57:21 GMT
FROM:    Rahul Gupta at NASA GSFC <rahul.gupta@nasa.gov>

T. Parsotan (GSFC), S. D. Barthelmy (GSFC), 
R. Gupta (GSFC), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC), M. J. Moss (GSFC),
D. M. Palmer (LANL), D. Sadaula (GSFC/UMBC),
T. Sakamoto (AGU), M. H. Siegel (PSU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250509A (trigger #1311764)
(Siegel, et al., GCN Circ. 40407).  The BAT ground-calculated position is
RA, Dec = 46.451, -38.854 deg which is 
   RA(J2000)  =  03h 05m 48.3s 
   Dec(J2000) = -38d 51' 15.1" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 96%.
 
The mask-weighted BAT light curve shows a sharp rise and exponential decay profile. 
T90 (15-350 keV) is 55.43 +- 10.47 sec (estimated error including systematics).
 
The time-averaged spectrum from T-2.85 to T+71.46 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.54 +- 0.08.  The fluence in the 15-150 keV band is 2.4 +- 0.1 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T+0.42 sec in the 15-150 keV band
is 1.9 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 
 
The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1311764