GCN Circular 35567

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, very bright GRB 240118A
(Fermi GBM observation: Hamburg et al., GCN 35563
Not found
 
 
;
Fermi LAT detection: Bissaldi et al., GCN 35560
Not found
 
 
;
NuSTAR detection: Grefenstette, GCN 35564
Not found
 
 
)
triggered Konus-Wind (KW) at T0=6508.107 s UT (01:48:28.107).

The burst light curve shows a multi-peaked structure,
which starts at ~T0-2.4 s, peaks at ~T0+37.5 s,
and has a total duration of ~90 s.
The emission is seen up to ~15 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB240118_T06508/

As observed by Konus-Wind, the burst had
a fluence of (8.24 ± 0.38)x10^-4 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 37.568 s,
of (6.65 ± 0.63)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+90.880 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 = -0.69 (-0.03,+0.03),
the high energy photon index beta = -2.37 (-0.05,+0.05),
the peak energy Ep = 402 (-12,+13) keV,
chi2 = 167/97 dof.

The spectrum near the peak count rate (measured from T0+36.352 s to T0+38.144 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 = -0.61 (-0.06,+0.07),
the high energy photon index beta = -2.62 (-0.21,+0.15),
the peak energy Ep = 634 (-51,+55) keV,
chi2 = 74/66 dof.

All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.