GCN Circular 37701
Subject
Konus-Wind detection of GRB 240926A
Date
2024-10-03T18:09:39Z (5 months ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Via
legacy email
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 GRB 240926A
(SVOM/GRM observation: Zhang et al., GCN 37616;
IPN triangulation: Kozyrev et al., GCN 37639)
triggered Konus-Wind (KW) at T0=42164.378 s UT (11:42:44.378).
The burst light curve shows a multi-peaked structure,
which starts at ~T0-16 s, peaks at ~T0+31 s,
and has a total duration of ~75 s.
The emission is seen up to ~3 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB240926_T42164/
As observed by Konus-Wind, the burst had
a fluence of (5.89 ± 0.59)x10^-5 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 31.424 s,
of (9.03 ± 0.85)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum (measured from T0 to T0+62.720 s)
is best fit in the 20 keV - 15 MeV range
by a GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.65 (-0.05,+0.06),
the high energy photon index beta = -2.60 (-0.55,+0.21),
the peak energy Ep = 118 (-11,+12) keV,
chi2 = 119/97 dof.
The spectrum near the peak count rate (measured from T0+31.232 s to T0+38.144 s)
is best fit in the 20 keV - 15 MeV range by a power law with exponential
cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.55(-0.07,+0.07) and Ep = 151(-14,+17) keV (chi2 = 98/80 dof).
Fitting this spectrum by a Band function yields the same values of alpha and Ep,
and an upper limit on the high energy photon index beta of -2.6 (chi2 = 98/79 dof).
All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.