TITLE:   GCN CIRCULAR
NUMBER:  21186
SUBJECT: GRB 170531B: Swift-BAT refined analysis
DATE:    17/06/01 16:18:59 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), P. A. Evans (U Leicester),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), 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+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 170531B (trigger #755354)
(Evans et al., GCN Circ. 21171).  The BAT ground-calculated position is
RA, Dec = 286.901, -16.414 deg which is
  RA(J2000)  =  19h 07m 36.3s
  Dec(J2000) = -16d 24' 51.6"
with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 96%.

The mask-weighted light curve shows a multi-peaked structure that starts
at ~T0 and ends at ~T+180 s. T90 (15-350 keV) is 164.13 +- 8.82 sec
(estimated error including systematics).

The time-averaged spectrum from T+0.55 to T+181.67 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.95 +- 0.14.  The fluence in the 15-150 keV band is 2.0 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+42.71 sec in the 15-150 keV band
is 0.8 +- 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/755354/BA/