TITLE:   GCN CIRCULAR
NUMBER:  15155
SUBJECT: GRB 130831A, Swift-BAT refined analysis
DATE:    13/09/01 04:15:22 GMT
FROM:    Tilan Ukwatta at MSU  <tilan.ukwatta@gmail.com>

S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL),
N. Gehrels (GSFC), L. M. Z. Hagen (PSU),
H. A. Krimm (GSFC/USRA), A. Y. Lien (NASA/GSFC/ORAU),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), G. Sato (ISAS), M. Stamatikos (OSU),
J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):

Using the data set from T-61 to T+243 sec from the
recent telemetry downlink, we report further analysis
of BAT GRB 130831A (trigger #568849) (Hagen, et al.,
GCN Circ. 130831A). The BAT ground-calculated position is
RA, Dec = 358.635, 29.431 deg which is
   RA(J2000)  =  23h 54m 32.4s
   Dec(J2000) = +29d 25' 51.4"
with an uncertainty of 1.0 arcmin, (radius, sys+stat,
90% containment). The partial coding was 28%.

BAT mask-weighted light curve shows a bright peak
starting from ~T-1 sec peaking around T+3 sec
and ending at ~T+12 sec. Two more very weak
emission can be seen around T+20 sec and T+32 sec.
T90 (15-350 keV) is 32.5 +- 2.5 sec
(estimated error including systematics).

The time-averaged spectrum from T-1.86 to T+41.38 sec
is best fit by a simple power-law model. The power
law index of the time-averaged spectrum is 1.93 +- 0.05.
The fluence in the 15-150 keV band is
6.5 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon
flux measured from T+2.30 sec in the 15-150 keV band
is 13.6 +- 0.6 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/568849/BA/