TITLE:   GCN CIRCULAR
NUMBER:  28484
SUBJECT: GRB 200922A: Swift-BAT refined analysis
DATE:    20/09/23 14:47:47 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), M. J. Moss (GWU),
D. M. Palmer (LANL), M. Stamatikos (OSU),
T. N. Ukwatta (LANL) (i.e. the Swift-BAT team):

Using the data set from T-239 to T+871 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 200922A (trigger #997024)
(Moss et al., GCN Circ. 28471).  The BAT ground-calculated position is
RA, Dec = 296.954, -55.199 deg which is
   RA(J2000)  =  19h 47m 49.0s
   Dec(J2000) = -55d 11' 55.1"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 74%.

The mask-weighted light curve shows a single FRED-like pulse that
starts at ~T-2 s, peaks at ~T+0, and ends at ~T+16 s.
T90 (15-350 keV) is 10.30 +- 1.96 sec (estimated error including
systematics).

The time-averaged spectrum from T-1.91 to T+16.22 sec is best fit
by a power law with an exponential cutoff.  This fit gives a photon
index 1.43 +- 0.26, and Epeak of 39.3 +- 5.7 keV (chi squared 52.48
for 56 d.o.f.).  For this model the total fluence in the 15-150 keV
band is 2.8 +- 0.1 x 10^-6 erg/cm2 and the 1-sec peak flux measured
from T-0.46 sec in the 15-150 keV band is 11.4 +- 0.5 ph/cm2/sec.
A fit to a simple power law gives a photon index of 2.12 +- 0.06
(chi squared 76.50 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/997024/BA/