GCN Circular 32600
Subject
Konus-Wind detection of GRB 220927A
Event
Date
2022-09-29T20:38:34Z (3 years ago)
From
Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>
A.Ridnaia, D. Frederiks, A.Lysenko, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The long-duration GRB 220927A
(Fermi-GBM detection: Fermi GBM Team, GCN 32594;
IPN triangulation: Kozyrev et al., GCN 32597)
triggered Konus-Wind at T0=20180.364 s UT (05:36:20.364).
The burst light curve shows a multipeaked initial emission
episode which starts at ~T0-1.9 s and ends at ~T0+8.3 s,
followed by a weaker episode at ~T0+35 s.
The total burst duration is ~46.7 s.
The emission is seen up to 2 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB220927_T20180/
As observed by Konus-Wind, the burst
had a fluence of 4.18(-1.08,+1.60)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0+3.968 s,
of 9.37(-2.57,+2.78)x10^-7 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum of the burst
(measured from T0 to T0+41.216 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.37(-0.77,+2.06),
the high energy photon index beta = -2.60(-7.40,+0.35),
the peak energy Ep = 40(-22,+15) keV,
chi2 = 93/96 dof.
The spectrum near the maximum count rate
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.97(-0.43,+0.61),
the high energy photon index beta = -3.04(-6.96,+0.44),
the peak energy Ep = 48(-6,+6) keV,
chi2 = 83/94 dof.
All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.