TITLE:   GCN CIRCULAR
NUMBER:  30580
SUBJECT: GRB 210731A: Swift-BAT refined analysis
DATE:    21/08/01 21:12:47 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

M. Stamatikos (OSU), S. D. Barthelmy (GSFC),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU),
E. Troja (NASA/GSFC/UMCP) T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):

Using the data set from T-239 to T+409 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 210731A (trigger #1062336)
(Troja et al., GCN Circ. 30568).  The BAT ground-calculated position is
RA, Dec = 300.311, -28.056 deg which is
   RA(J2000)  =  20h 01m 14.5s
   Dec(J2000) = -28d 03' 20.0"
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 39%.

The mask-weighted light curve shows a single-pulse structure that
starts at ~T-1 s, peaks at ~T+11 s, and ends at ~T+30 s.
T90 (15-350 keV) is 22.51 +- 2.79 sec (estimated error
including systematics).

The time-averaged spectrum from T-0.78 to T+25.50 sec is best fit
by a power law with an exponential cutoff.  This fit gives a photon
index -0.25 +- 0.59, and Epeak of 106.5 +- 26.8 keV (chi squared
50.28 for 56 d.o.f.).  For this model the total fluence in the 15-150 keV
band is 2.2 +- 0.2 x 10^-6 erg/cm2 and the 1-sec peak flux measured
from T+11.28 sec in the 15-150 keV band is 1.6 +- 0.3 ph/cm2/sec.
A fit to a simple power law gives a photon index of 1.01 +- 0.11
(chi squared 67.96 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/1062336/BA/