GCN Circular 36907

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 240718A
(Fermi-GBM detection: Fermi GBM team, GCN 36898
Not found
 
 
;
Preis et al., GCN 36899
Not found
 
 
; de Barra & Meegan, GCN 36903
Not found
 
 
;
SVOM/GRM observation: Zhang et al., GCN 36900
Not found
 
 
;
Fermi-LAT detection: Depalo et al., GCN 36901
Not found
 
 
)
triggered Konus-Wind at T0=23345.357 s UT (06:29:05.357).

The burst light curve shows a multipeaked structure
which starts at ~T0-0.2 s and has a total duration of ~53 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/GRB240718_T23345/

As observed by Konus-Wind, the burst
had a fluence of 1.22(-0.11,+0.11)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+0.560 s,
of 5.04(-0.58,+0.59)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+59.648 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 = -0.91(-0.08,+0.08)
and Ep = 1355(-178,+213) keV (chi2 = 115/83 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.4
(chi2 = 115/82 dof).

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+2.304 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model
with  alpha = -0.38(-0.08,+0.08)
and Ep = 1126(-77,+82) keV (chi2 = 67/63 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.6
(chi2 = 67/62 dof).

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.