TITLE:   GCN CIRCULAR
NUMBER:  18328
SUBJECT: GRB 150915A, Swift-BAT refined analysis
DATE:    15/09/17 09:05:19 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

D. M. Palmer (LANL), S. D. Barthelmy (GSFC),  J. R. Cummings (GSFC/UMBC),
V. D'Elia (ASDC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), 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 150915A (trigger #655721)
(D'Elia, et al., GCN Circ. 18315).  The BAT ground-calculated position is
RA, Dec = 319.675, -34.874 deg which is
  RA(J2000)  =  21h 18m 42.0s
  Dec(J2000) = -34d -52' -27.1"
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 55%.

The mask-weighted light curve shows a weak complex structure that starts
at ~ T0-70 s and ends at ~T0+120 s. There might be additional weak emission
that starts since the beginning of the event data. T90 (15-350 keV)
is 164.7 +- 49.7 sec (estimated error including systematics).

The time-averaged spectrum from T-69.0 to T+116.8 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.51 +- 0.42.  The fluence in the 15-150 keV band is 8.0 +- 1.8 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+17.68 sec in the 15-150 keV band
is 0.5 +- 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/655721/BA/