TITLE:   GCN CIRCULAR
NUMBER:  23054
SUBJECT: GRB 180728A: Swift-BAT refined analysis
DATE:    18/07/29 16:17:30 GMT
FROM:    Hans Krimm at NASA-GSFC/NSF  <hans.krimm@nasa.gov>

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

Using the data set from T-239 to T+667 sec from the recent telemetry 
downlink,
we report further analysis of BAT GRB 180728A (trigger #850471)
(Starling, et al., GCN Circ. 23046).  The BAT ground-calculated position is
RA, Dec = 253.574, -54.037 deg which is
    RA(J2000)  =  16h 54m 17.7s
    Dec(J2000) = -54d 02' 13.7"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 57%.

The mask-weighted light curve shows a relatively faint, soft precursor 
near the
trigger time, lasting about 3 seconds.  This was followed by a single, much
brighter pulse, which consisted of two overlapping peaks.   This pulse 
began at
T+11 sec, peaked at T+13 sec, and faded to background by T+40 sec.
T90 (15-350 keV) is 8.68 +- 0.30 sec (estimated error including 
systematics).

The time-averaged spectrum from T-0.24 to T+36.51 sec is best fit by a 
simple
power-law model.  The power law index of the time-averaged spectrum is
1.97 +- 0.03.  The fluence in the 15-150 keV band is 2.96 +- 0.06 x 
10^-5 erg/cm2.
The 1-sec peak photon flux measured from T+12.61 sec in the 15-150 keV band
is 132.0 +- 2.9 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/850471/BA/