TITLE:   GCN CIRCULAR
NUMBER:  40121
SUBJECT: Konus-Wind detection of GRB 250407A
DATE:    25/04/08 16:13:31 GMT
FROM:    Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>

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-duration GRB 250407A ( Fermi-GBM detection:
The Fermi GBM team, GCN 40104; Mukherjee & Meegan, GCN 40114;
SVOM/GRM observation: Wang et al., GCN 40120)
triggered Konus-Wind (KW) at T0=56895.249 s UT (15:48:15.249).
The burst afterglow was detected and localized
by SRG/ART-XC (Molkov et al. 2025, GCN 40110)
and Swift-XRT (Dichiara et al. 2025, GCN 40113).

The burst light curve shows a bright pulse
which starts at ~T0-6 s and has a total duration of ~20 s.
A weaker emission can be traced at least to ~T0+50 s.
The emission in the main pulse is seen up to ~15 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250407_T56895/

As observed by Konus-Wind, the burst had
a fluence of (1.57 ± 0.04)x10^-4 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 5.292 s,
of (1.41 ± 0.05)x10^-4 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+15.616 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 = -1.02 (-0.03,+0.03),
the high energy photon index beta = -2.27 (-0.07,+0.06),
the peak energy Ep = 648 (-44,+46) keV,
chi2 = 162/97 dof.

The spectrum near the peak count rate (measured from T0+5.888 s to T0+7.424 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 = -0.76 (-0.06,+0.07),
the high energy photon index beta = -2.38 (-0.14,+0.11),
the peak energy Ep = 833 (-99,+106) keV,
chi2 = 78/65 dof.

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