TITLE:   GCN CIRCULAR
NUMBER:  21877
SUBJECT: GRB 170912A: Swift-BAT refined analysis
DATE:    17/09/12 21:42:52 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

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

Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 170912A (trigger #772006)
(Tohuvavohu et al., GCN Circ. 21861).  The BAT ground-calculated position is
RA, Dec = 167.386, -54.343 deg which is
  RA(J2000)  =  11h 09m 32.6s
  Dec(J2000) = -54d 20' 35.4"
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 34%.

The mask-weighted light curve shows a single-peaked structure that starts
at ~T0, peaks at ~T+3, and ends at ~T+25 s. T90 (15-350 keV) is
21.9 +- 5.6 sec (estimated error including systematics).

The time-averaged spectrum from T-0.42 to T+25.64 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.04 +- 0.21.  The fluence in the 15-150 keV band is 1.1 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+2.38 sec in the 15-150 keV band
is 2.0 +- 0.4 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/772006/BA/