GCN Circular 23155

J. R. Cummings (CPI), S. D. Barthelmy (GSFC),
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 180818B (trigger #853882)
(Marshall et al., GCN Circ. 23149
Not found
 
 
).  The BAT ground-calculated position is
RA, Dec = 104.227, 39.310 deg which is
  RA(J2000)  =  06h 56m 54.5s
  Dec(J2000) = +39d 18' 35.1"
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 89%.

The mask-weighted light curve shows two pulses. The first pulse starts at
at ~T-100 s, peaks at ~T-80 s, and ends at ~T-50 s. The second pulse starts
at ~T+10 s, peaks at ~T+30 s, and ends at ~T+60 s. T90 (15-350 keV) is
134.4 +- 9.8 sec (estimated error including systematics). However, note that
the burst came into the BAT FOV at ~T-128 s, and thus there might be additional
burst emission beforehand.

The time-averaged spectrum from T-93.58 to T+62.74 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.77 +- 0.12.  The fluence in the 15-150 keV band is 2.3 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-82.11 sec in the 15-150 keV band
is 1.2 +- 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/853882/BA/