GCN Circular 41942
Subject
Konus-Wind detection of GRB 250920B
Event
Date
2025-09-22T18:37:52Z (8 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 long-duration GRB 250920B
(Fermi-GBM detection: The Fermi GBM team, GCN 41897;
Sonawane and Meegan, GCN 41919;
Swift-BAT detection: Gupta et al., GCN 41898;
Sakamoto et al., GCN 41923;
Glowbug detection: Cheung et al., GCN 41937)
triggered Konus-Wind at T0=31587.304 s UT (08:46:27.304).
The burst light curve shows a multipeaked structure
which starts at ~T0-3.0 s and has a total duration of ~141 s.
The emission is seen up to ~10 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250920_T31587/
As observed by Konus-Wind, the burst
had the total fluence of 3.80(-0.78,+0.93)x10^-5 erg/cm2,
and the 64-ms peak flux, measured from T0+6.368 s,
of 6.72(-1.17,+1.16)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst
(measured from T0 to T0+131.328 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 = -1.41(-0.10,+0.11),
the high energy photon index beta = -2.41(-7.59,+0.35),
the peak energy Ep = 310(-69,+94) keV
(chi2 = 94/97 dof).
The spectrum near the maximum count rate
(measured from T0+0.256 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 = -1.06(-0.10,+0.10),
the high energy photon index beta = -2.33(-0.38,+0.18),
the peak energy Ep = 296(-38,+52) keV
(chi2 = 87/81 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.