TITLE:   GCN CIRCULAR
NUMBER:  22584
SUBJECT: GRB 180402A, Swift-BAT refined analysis
DATE:    18/04/02 19:58:51 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

T. N. Ukwatta (LANL), 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),
M. Stamatikos (OSU) (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 180402A (trigger #821103)
(Lien et al., GCN Circ. 22580).  The BAT ground-calculated position is
RA, Dec = 251.923, -14.928 deg which is
  RA(J2000)  =  16h 47m 41.6s
  Dec(J2000) = -14d 55' 41.6"
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 37%.

The mask-weighted light curve shows a single short pulse that starts
at ~T0, peaks at ~0.1 s, and ends at ~0.3 s T90 (15-350 keV) is 0.18 +- 0.03 sec
(estimated error including systematics). The ground analysis confirmed
that the additional variation seen in the raw light curve are indeed from
MAXI J1820+070 (Lien et al., GCN Circ. 22580).

The time-averaged spectrum from T+0.05 to T+0.26 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
0.52 +- 0.30.  The fluence in the 15-150 keV band is 1.4 +- 0.2 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.34 sec in the 15-150 keV band
is 1.8 +- 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/821103/BA/