TITLE:   GCN CIRCULAR
NUMBER:  23001
SUBJECT: GRB 180721A: Swift-BAT refined analysis
DATE:    18/07/21 19:01:43 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

H. A. Krimm (NSF/USRA), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), B. Sbarufatti (PSU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):

Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180721A (trigger #849018)
(Sbarufatti et al., GCN Circ. 22994).  The BAT ground-calculated position is
RA, Dec = 347.708, 4.871 deg which is
  RA(J2000)  =  23h 10m 49.9s
  Dec(J2000) = +04d 52' 16.1"
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.

The mask-weighted light curve shows a single-pulse structure that starts
at ~T-1 s, peaks at ~T+2 s, and ends at ~T+10 s. The main pulse is followed
by some weak emission that last till ~T+50 s. T90 (15-350 keV) is 47.6 +- 3.0 sec
(estimated error including systematics).

The time-averaged spectrum from T-0.39 to T+48.92 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.25 +- 0.22.  The fluence in the 15-150 keV band is 5.9 +- 0.9 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+1.82 sec in the 15-150 keV band
is 0.9 +- 0.1 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/849018/BA/