TITLE:   GCN CIRCULAR
NUMBER:  34623
SUBJECT: GRB 230903A: Swift-BAT refined analysis
DATE:    23/09/05 04:07:26 GMT
FROM:    Mike Moss at George Washington U <mikejmoss3@gmail.com>

M. J. Moss (GSFC),
S. D. Barthelmy (GSFC), 
A. D'Ai (INAF-IASFPA),
H. A. Krimm (NSF),
S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC),
D. M. Palmer (LANL),
T. Parsotan (GSFC/UMBC),
T. Sakamoto (AGU),
M. Stamatikos (OSU)
(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 230903A (trigger #1189514)
(D'Ai, et al., GCN Circ. 34610).  The BAT ground-calculated position is
RA, Dec = 9.898, -40.910 deg which is 
   RA(J2000)  =  00h 39m 35.5s 
   Dec(J2000) = -40d 54' 34.5" 
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 40%.
 
The mask weighted light curve shows a single short pulse. T90 (15-350 keV) is 2.54 +- 0.27 sec (estimated error including systematics). 
The T90 and the spectral hardness of this burst places it on the border of the long-soft and hard-short burst classifications. 
 
The time-averaged spectrum from T+0.20 to T+2.93 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index -0.66 +- 1.49, 
and Epeak of 63.4 +- 17.8 keV (chi squared 44.41 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 2.2 +- 0.4 x 10^-07 erg/cm2
and the 1-sec peak flux measured from T+0.50 sec in the 15-150 keV band is
1.3 +- 0.3 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.40 +- 0.21 (chi squared 54.66 for 57 d.o.f.).  All the quoted errors
are at the 90% confidence level. 
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/1189514/BA/