TITLE:   GCN CIRCULAR
NUMBER:  18214
SUBJECT: GRB 150831A: Swift-BAT refined analysis
DATE:    15/08/31 19:08:41 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

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

Using the data set from T-240 to T+938 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 150831A (trigger #653838)
(Lien, et al., GCN Circ. 18209).  The BAT ground-calculated position is
RA, Dec = 221.034, -25.619 deg which is
  RA(J2000)  =  14h 44m 08.1s
  Dec(J2000) = -25d 37' 08.4"
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 52%.

The mask-weighted light curve shows a short pulse that starts and peaks
at ~ T0, and ends at ~ T+1.4 s. T90 (15-350 keV) is 1.15 +- 0.23 sec
(estimated error including systematics).

The time-averaged spectrum from T-0.03 to T+1.40 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
0.81 +- 0.16.  The fluence in the 15-150 keV band is 3.8 +- 0.3 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.0 sec in the 15-150 keV band
is 3.4 +- 0.3 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

The lag analysis using 8-ms binned light curve gives a spectral lag
of -2 ms +-  5 ms for the 100-350 keV and 25-50 keV band,
and 13 ms +- 20 ms for the 50-100 keV and 15-25 keV band.
These values are consistent with short GRBs.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/653838/BA/