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GCN Circular 33598

Subject
GRB 230409B: Swift-BAT refined analysis
Date
2023-04-09T17:50:01Z (a year ago)
From
Amy Lien at GSFC <amy.y.lien@nasa.gov>
D. M. Palmer (LANL), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC), T. Parsotan (GSFC/UMBC),
T. Sakamoto (AGU), M. Stamatikos (OSU)
(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 230409B (trigger #1163401)
(Beardmore et al., GCN Circ. 33592).  The BAT ground-calculated position
is RA, Dec = 329.516, 52.832 deg which is
   RA(J2000)  =  21h 58m 03.8s
   Dec(J2000) = +52d 49' 55.1"
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 32%.

The mask-weighted light curve shows a single-pulse structure
that starts at ~T-1 s, peaks at ~T+1 s, and ends at ~T+12 s.
The hump at ~50 s to 100 s mentioned in the previous circular
(Beardmore et al., GCN Circ. 33592) is due to background fluctuation
and is not part of the burst. T90 (15-350 keV) is 9.79 +- 2.59 sec
(estimated error including systematics).

The time-averaged spectrum from T-0.58 to T+11.78 sec is best fit by a
simple
power-law model.  The power law index of the time-averaged spectrum is
1.86 +- 0.19.  The fluence in the 15-150 keV band is 9.9 +- 1.2 x 10^-7
erg/cm2.
The 1-sec peak photon flux measured from T+0.43 sec in the 15-150 keV band
is 3.7 +- 0.5 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/1163401/BA/
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