GCN Circular 41295
Subject
Konus-Wind detection of GRB 250807A
Event
Date
2025-08-08T18:25:17Z (12 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 250807A
(Swift-BAT detection: Klingler et al., GCN 41262;
AstroSat-CZTI detection: Salunke et al., GCN 41281;
SVOM-GRM detection: Wang et al., GCN 41283)
triggered Konus-Wind at T0=38766.990 s UT (10:46:06.990).
The burst light curve shows a multipeaked structure
which starts at ~T0-2.3 s and has a total duration of ~79 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/GRB250807_T38766/
As observed by Konus-Wind, the burst
had the total fluence of 1.03(-0.09,+0.08)x10^-4 erg/cm2,
and the 64-ms peak flux, measured from T0+35.904 s,
of 1.11(-0.10,+0.10)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+79.104 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 = -1.04(-0.04,+0.04),
the high energy photon index beta = -2.74(-0.66,+0.26),
the peak energy Ep = 369(-26,+26) keV
(chi2 = 132/97 dof).
The spectrum near the maximum count rate
(measured from T0+29.952 to T0+38.144 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.04(-0.05,+0.05)
and Ep = 390(-25,+28) keV (chi2 = 105/86 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.5
(chi2 = 105/85 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.