TITLE:   GCN CIRCULAR
NUMBER:  22576
SUBJECT: GRB 180331B: Swift-BAT refined analysis
DATE:    18/03/31 23:43:44 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

M. Stamatikos (OSU), 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), T. Sakamoto (AGU),
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 180331B (trigger #820513)
(Lien et al., GCN Circ. 22573).  The BAT ground-calculated position is
RA, Dec = 196.781, 61.735 deg which is
  RA(J2000)  =  13h 07m 07.6s
  Dec(J2000) = +61d 44' 05.9"
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 30%.

The mask-weighted light curve shows a double-peaked structure that starts
at ~T-20 s and ends at ~T+140 s. The two peaks occur at ~T-20 s and ~T+1 s,
respectively. T90 (15-350 keV) is 147.0 +- 33.1 sec (estimated error including systematics).

The time-averaged spectrum from T-22.03 to T+142.97 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.48 +- 0.22.  The fluence in the 15-150 keV band is 1.9 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+0.97 sec in the 15-150 keV band
is 2.8 +- 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/820513/BA/