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GCN Circular 23123

Subject
GRB 180809B, Swift-BAT refined analysis
Date
2018-08-10T18:20:37Z (6 years ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
M. Stamatikos (OSU), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF/USRA),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
M. J. Moss (GWU), D. M. Palmer (LANL),
T. Sakamoto (AGU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):

Using the data set from T-240 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 180809B (trigger #852553)
(Moss et al., GCN Circ. 23105).  The BAT ground-calculated position is
RA, Dec = 299.712, -15.293 deg which is
  RA(J2000)  =  19h 58m 50.8s
  Dec(J2000) = -15d 17' 34.0"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 63%.

The mask-weighted light curve shows a multi-peaked structure that starts
at ~T-36 s and ends at ~T+80 s, followed by another pulse that starts
at ~T+200 s and ends at ~T+250 s. The total burst emission ends at ~T+300 s.
T90 (15-350 keV) is 233.2 +- 1.1 sec (estimated error including systematics).

We note that the later pulse overlaps with the XRT flare and some ground-based
optical observations (e.g. Tiurina et al.; GCN #23113), which indicates an increase
 in the optical magnitude from Mag 16.5 to 15.5 at the pulse time.

The time-averaged spectrum from T-36.1 to T+302.3 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.26 +- 0.02.  The fluence in the 15-150 keV band is 7.3 +- 0.1 x 10^-5 erg/cm2.
The 1-sec peak photon flux measured from T+35.10 sec in the 15-150 keV band
is 26.3 +- 0.6 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/852553/BA/
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