GCN Circular 39720
Subject
Konus-Wind detection of GRB 250308A
Date
2025-03-14T15:54:17Z (4 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 short-duration GRB 250308A
(SVOM-GRM detection: Wang et al., GCNs 39632, 39636;
IPN triangulation: Kozyrev et al., GCN 39653;
CALET-GBM detection: Kawakubo et al., GCN 39663;
Swift-BAT/GUANO detection: DeLaunay et al., GCN 39676)
triggered Konus-Wind at T0=65194.997 s UT (18:06:34.997).
The burst light curve shows a multipeaked structure
which starts at ~T0-40 ms and has a total duration of ~0.4 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/GRB250308_T65194/
As observed by Konus-Wind, the burst
had a fluence of 8.23(-0.52,+0.54)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0-6 ms,
of 5.24(-0.69,+0.70)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+0.256 s)
is best fit in the 20 keV - 5 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.41(-0.12,+0.13)
and Ep = 1176(-109,+125) keV (chi2 = 60/52 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.9
(chi2 = 60/51 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.