TITLE:   GCN CIRCULAR
NUMBER:  23357
SUBJECT: GRB 181020A: Swift-BAT refined analysis
DATE:    18/10/21 14:50:33 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@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),
M. J. Moss (GWU), 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 181020A (trigger #867987)
(Moss et al., GCN Circ. 23349).  The BAT ground-calculated position is
RA, Dec = 13.987, -47.372 deg which is 
  RA(J2000)  =  00h 55m 56.9s 
  Dec(J2000) = -47d 22' 18.1" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 94%.

The mask-weighted light curve shows a large pulse that starts at ~T-1 s, peaks
at ~T+8 s and ends at ~T+30 s. There is a second, much weaker, pulse that occurs
at ~T+200 s and lasts until ~T+270 s. T90 (15-350 keV) is 238.0 +- 11.6 sec 
(estimated error including systematics).

The time-averaged spectrum from T-1.45 to T+271.20 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.25 +- 0.06.  The fluence in the 15-150 keV band is 8.1 +- 0.3 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+7.26 sec in the 15-150 keV band
is 7.7 +- 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/867987/BA/