GCN Circular 42527
Subject
Konus-Wind detection of GRB 251028A
Event
Date
2025-10-31T16:09:13Z (3 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 251028A
(Ferm-GBM detection: The Fermi GBM team, GCN 42497;
Veres and Meegan, GCN 42520;
BALROG localization: Preis & Greiner, GCN 42499;
MAXI-GSC detection: Sugai et al., GCN 42498;
Glowbug detection: Cheung et al., GCN 42506;
SVOM-GRM detection: Guo et al., GCN 42522;
GECAM-B detection: Guo et al., GCN 42523)
triggered Konus-Wind at T0=12396.343 s UT (03:26:36.343).
The burst light curve starts with a possible rise of a weak emission at ~T0-67 s,
which, at ~T0-5.5 s, evolves into the main multi-peaked emission episode
with a duration of ~38 s.
The emission is seen up to ~5 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB251028_T12396/
As observed by Konus-Wind, the burst
had the total fluence of 3.95(-0.25,+0.27)x10^-5 erg/cm2,
and the 64-ms peak flux, measured from T0+19.568 s,
of 3.17(-0.62,+0.64)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the main episode
(measured from T0 to T0+33.024 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 = -0.70(-0.12,+0.13),
the high energy photon index beta = -2.81(-0.39,+0.22),
the peak energy Ep = 229(-15,+16) keV
(chi2 = 92/97 dof).
The spectrum near the maximum count rate
(measured from T0+16.640 to T0+24.832 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 = -0.31(-0.20,+0.22),
the high energy photon index beta = -3.22(-1.23,+0.42),
the peak energy Ep = 217(-15,+17) keV
(chi2 = 77/82 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.