TITLE:   GCN CIRCULAR
NUMBER:  21879
SUBJECT: GRB 170912B: Swift-BAT refined analysis
DATE:    17/09/13 01:42:01 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

D. M. Palmer (LANL), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF/USRA),
S. J. LaPorte (PSU), 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-240 to T+480 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 170912B (trigger #772052)
(LaPorte et al., GCN Circ. 21864).  The BAT ground-calculated position is
RA, Dec = 215.464, -61.997 deg which is
  RA(J2000)  =  14h 21m 51.3s
  Dec(J2000) = -61d 59' 50.8"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.

The mask-weighted light curve shows several overlapping pulses that starts
at ~ T0 and ends at ~ T+40 s. T90 (15-350 keV) is 19.6 +- 6.2 sec
(estimated error including systematics).

The time-averaged spectrum from T-0.93 to T+38.75 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.88 +- 0.07.  The fluence in the 15-150 keV band is 2.4 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-0.07 sec in the 15-150 keV band
is 5.7 +- 0.3 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/772052/BA/