GCN Circular 37603
Subject
Konus-Wind detection of GRB 240918B
Event
Date
2024-09-24T19:27:38Z (a year ago)
From
Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>
Via
Web form
A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The long-duration GRB 240918B
(Fermi-GBM detection: The Fermi GBM team, GCN 37558;
INTEGRAL SPI-ACS detection: Pawar, GCN 37560;
AstroSat CZTI detection: Joshi et al., GCN 37588;
IPN triangulation: Kozyrev et al., GCN 37602)
triggered Konus-Wind at T0=75415.787 s UT (20:56:55.787).
The burst light curve shows a multipeaked structure
which starts at ~T0-1.9 s and has a total duration of ~4.4 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/GRB240918_T75415/
As observed by Konus-Wind, the burst
had a fluence of 4.19(-0.60,+0.71)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0+1.264 s,
of 2.56(-0.89,+0.93)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+8.448 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 = -0.49(-0.44,+0.56)
and Ep = 173(-28,+45) keV (chi2 = 112/99 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.2
(chi2 = 111/98 dof).
All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.