GCN Circular 41941
Subject
Konus-Wind detection of GRB 250920A
Event
Date
2025-09-22T18:33:59Z (2 days ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
Via
Web form
D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia,
A. Tsvetkova, M. Ulanov, and T. Cline
on behalf of the Konus-Wind team, report:
The bright, long-duration GRB 250920A
(Ferm-GBM detection: The Fermi GBM team, GCN 41895;
Sonawane and Smith, GCN 41918;
BALROG localization: Preis and Greiner, GCN 41896
AstroSat-CZTI detection: Harsha et al., GCN 41899;
SVOM-GRM detection: Wang et al., GCN 41912;
NuSTAR-detection: Waratkar et al., GCN 41926;
IPN triangulation: Kozyrev et al., GCN 41940)
triggered Konus-Wind at T0=10444.538 s UT (02:54:04.538).
The burst light curve shows a multipeaked structure
which starts at ~T0-1.1 s and has a total duration of ~12.5 s.
The emission is seen up to ~15 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250920_T10444/
There are no data for the ~18-70 keV band in the triggered mode.
As observed by Konus-Wind, the burst
had the total fluence of 4.52(-0.15,+0.15)x10^-5 erg/cm2,
and the 64-ms peak flux, measured from T0+1.984 s,
of 4.06(-0.28,+0.28)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst
(measured from T0 to T0+18.432 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 = -0.84(-0.05,+0.05),
the high energy photon index beta = -2.61(-0.09,+0.08),
the peak energy Ep = 162(-6,+6) keV
(chi2 = 106/97 dof).
The spectrum near the maximum count rate
(measured from T0+1.792 to T0+2.048 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 = -0.58(-0.09,+0.09),
the high energy photon index beta = -2.46(-0.14,+0.11),
the peak energy Ep = 332(-27,+31) keV
(chi2 = 44/46 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.