[vsnet-grb-info 20478] GRB 180331A: Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22574
SUBJECT: GRB 180331A: Swift-BAT refined analysis
DATE:    18/03/31 16:01:42 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien at nasa.gov>

T. Sakamoto (AGU), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF/USRA),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), 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 180331A (trigger #820347)
(Markwardt et al., GCN Circ. 22568).  The BAT ground-calculated position is
RA, Dec = 66.005, 13.386 deg which is
  RA(J2000)  =  04h 24m 01.1s
  Dec(J2000) = +13d 23' 09.2"
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 81%.

The mask-weighted light curve shows a weak pulse that starts at ~T0,
peaks at ~T+9 s, and ends at ~T+50 s. T90 (15-350 keV) is 48.0 +- 22.6 sec
(estimated error including systematics).

The time-averaged spectrum from T+0.58 to T+48.58 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.11 +- 1.04,
and Epeak of 66.1 +- 28.3 keV (chi squared 57.70 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 6.1 +- 1.0 x 10^-7 erg/cm2
and the 1-sec peak flux measured from T+8.08 sec in the 15-150 keV band is
0.5 +- 0.1 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.46 +- 0.19 (chi squared 64.59 for 57 d.o.f.).  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/820347/BA/