TITLE:   GCN CIRCULAR
NUMBER:  23154
SUBJECT: GRB 180818A: Swift-BAT refined analysis
DATE:    18/08/19 01:00:13 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

S. D. Barthelmy (GSFC), J. R. Cummings (CPI),
H. A. Krimm (NSF/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), F. E. Marshall (NASA/GSFC),
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-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180818A (trigger #853824)
(Marshall et al., GCN Circ. 23146).  The BAT ground-calculated position is
RA, Dec = 169.698, -48.344 deg which is
  RA(J2000)  =  11h 18m 47.5s
  Dec(J2000) = -48d 20' 37.9"
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 78%.

The mask-weighted light curve shows a single-pulsed structure that starts
at ~T-2 s, peaks at ~T+2 s, and ends at ~T+14 s. T90 (15-350 keV) is
13.7 +- 4.1 sec (estimated error including systematics).

The time-averaged spectrum from T-2.14 to T+14.10 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.15 +- 0.36.  The fluence in the 15-150 keV band is 2.6 +- 0.6 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+1.64 sec in the 15-150 keV band
is 0.6 +- 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/853824/BA/