TITLE:   GCN CIRCULAR
NUMBER:  27273
SUBJECT: GRB 200228B: Swift-BAT refined analysis
DATE:    20/02/29 23:49:33 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC),
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-240 to T+297 sec from the recent telemetry
downlink,
we report further analysis of BAT GRB 200228B (trigger #958733)
(Laha et al., GCN Circ. 27254).  The BAT ground-calculated position is
RA, Dec = 252.007, 16.964 deg which is
   RA(J2000)  =  16h 48m 01.8s
   Dec(J2000) = +16d 57' 50.3"
with an uncertainty of 2.5 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 31%.

The mask-weighted light curve shows a weak pulse that starts at ~T-1 s,
peaks at ~T+2 s, and ends at ~T+7 s. T90 (15-350 keV) is 7.37 +- 1.58 sec
(estimated error including systematics).

The time-averaged spectrum from T-0.84 to T+6.97 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.27 +- 0.36.  The fluence in the 15-150 keV band is 3.0 +- 0.6 x 10^-7
erg/cm2.
The 1-sec peak photon flux measured from T+1.32 sec in the 15-150 keV band
is 1.0 +- 0.4 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/958733/BA/