[vsnet-grb-info 21077] GRB 180823A, Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23175
SUBJECT: GRB 180823A, Swift-BAT refined analysis 
DATE:    18/08/25 20:56:53 GMT
FROM:    Hans Krimm at NSF/NASA-GSFC  <hkrimm at nsf.gov>

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC),  J. R. Cummings (CPI),
H. A. Krimm (NSF/USRA), 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-43 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180823A (trigger #855434)
(Sbarufatti, et al., GCN Circ. 23169).  The BAT ground-calculated position is
RA, Dec = 210.358, 14.901 deg which is 
  RA(J2000)  =  14h 01m 25.9s 
  Dec(J2000) = +14d 54' 03.2" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 92%.

The available data starts as the burst is rising, but it appears that it includes the
entire burst.   The mask-weighted light curve shows a double-peaked structure, 
starting at ~T-43 seconds, with comparably sized peaks at ~T+5 and ~T+20 sec,
and returning to near background by T+70 seconds, with a fainter tail out past
T+100 seconds.  A spacecraft slew took the burst location out of the BAT field
of view around T+450 seconds. T90 (15-350 keV) is 80.3 +- 6.9 sec (estimated 
error including systematics).

The time-averaged spectrum from T-37.5 to T+72.0 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.58 +- 0.05.  The fluence in the 15-150 keV band is 7.8 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+18.33 sec in the 15-150 keV band
is 2.3 +- 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/855434/BA/