TITLE:   GCN CIRCULAR
NUMBER:  17604
SUBJECT: GRB 150318A: Swift-BAT refined analysis
DATE:    15/03/18 15:48:56 GMT
FROM:    Hans Krimm at NASA-GSFC  <hans.a.krimm@nasa.gov>

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC),  W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC), C. Pagani (U. Leicester), D. M. Palmer (LANL),
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+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 150318A (trigger #635289)
(Pagani, et al., GCN Circ. 17599).  The BAT ground-calculated position is
RA, Dec = 324.990, -61.461 deg, which is
    RA(J2000)  =  21h 39m 57.6s
    Dec(J2000) = -61d 27' 41.3"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 44%.

The mask-weighted light curve shows two very broad peaks.  The first one runs
from about T-10 sec to T+50 sec, and the second, brighter peak starts at T+50 sec,
peaks at ~T+65 sec and decays to background by T+120 sec.
T90 (15-350 keV) is 83.88 +- 12.57 sec (estimated error including systematics).

The time-averaged spectrum from T-6.60 to T+98.58 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.00 +- 0.12.  The fluence in the 15-150 keV band is 2.5 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+66.62 sec in the 15-150 keV band
is 1.1 +- 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/635289/BA/