GCN Circular 41939
Subject
Konus-Wind detection of GRB 250911A
Event
Date
2025-09-22T16:37:08Z (6 days ago)
From
Valentina Panteleeva at Ioffe Institute <panteleevav228@gmail.com>
Via
Web form
V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The long-duration GRB 250911A
(Swift-BAT detection: Klingler et al., GCN 41781;
Palmer et al., GCN 41812;
GECAM-B detection: Zhang et al., GCN 41813;
Insight-HXMT detection: Wang et al., GCN 41827)
triggered Konus-Wind at T0=05370.240 s UT (01:29:30.240).
The burst light curve shows a multipeaked structure
which starts at ~T0-2.3 s and has a total duration of ~57 s.
The weak precursor that triggered Swift-BAT is seen at ~T0-100 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/GRB250911_T05370/
As observed by Konus-Wind, the burst
had the total fluence of 4.54(-0.29,+0.30)x10^-5 erg/cm2,
and the 64-ms peak flux, measured from T0+1.440 s,
of 5.15(-0.88,+0.90)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+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 = -0.85(-0.11,+0.12),
the high energy photon index beta = -2.58(-0.19,+0.14),
the peak energy Ep = 196(-13,+14) keV
(chi2 = 102/97 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 = -0.92(-0.11,+0.12),
the high energy photon index beta = -2.44(-0.19,+0.14),
the peak energy Ep = 257(-25,+26) keV
(chi2 = 88/84 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.