TITLE:   GCN CIRCULAR
NUMBER:  26692
SUBJECT: GRB 200109A: Swift-BAT refined analysis
DATE:    20/01/09 21:24:27 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

H. A. Krimm (NSF), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), S. Laha (GSFC/UMBC),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
A. Melandri (INAF-OAB), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. Stamatikos (OSU),
T. N. Ukwatta (LANL) (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 200109A (trigger #948361)
(Melandri et al., GCN Circ. 26678).  The BAT ground-calculated position is
RA, Dec = 307.116, 52.988 deg which is
   RA(J2000)  =  20h 28m 27.7s
   Dec(J2000) = +52d 59' 17.7"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.

The mask-weighted light curve shows a weak structure with several
overlapping
pulses that start at ~T-30 s to ~T+20 s, followed by a weaker tail
emission that lasts till ~T+100 s. T90 (15-350 keV) is 112.0 +- 32.0 sec
(estimated error including systematics).

The time-averaged spectrum from T-31.45 to T+112.55 sec is best fit by a
simple
power-law model.  The power law index of the time-averaged spectrum is
1.31 +- 0.14.  The fluence in the 15-150 keV band is 2.1 +- 0.2 x 10^-6
erg/cm2.
The 1-sec peak photon flux measured from T+8.05 sec in the 15-150 keV band
is 0.7 +- 0.2 ph/cm2/sec.  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/948361/BA/