TITLE: GCN CIRCULAR NUMBER: 38895 SUBJECT: Konus-Wind detection of GRB 250107C DATE: 25/01/10 15:59:26 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 GRB 250107C (SVOM/GRM observation: Xue et al., GCN 38870; IPN triangulation: Svinkin et al., GCN 38879) triggered Konus-Wind (KW) at T0=67934.719 s UT (18:52:14.719).

The burst consists of two overlapping peaks and had the total duration of ~4 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/GRB250107_T67934/

As observed by Konus-Wind, the burst had a fluence of (3.02 ± 0.13)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0 + 0.960 s, of (2.23 ± 0.15)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+10.752 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 = -0.41 (-0.06,+0.06), the high energy photon index beta = -3.03 (-0.28,+0.18), the peak energy Ep = 254 (-10,+11) keV, chi2 = 78/79 dof.

The spectrum near the peak count rate (measured from T0+0.768 s to T0+1.024 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 = -0.01 (-0.13,+0.15), the high energy photon index beta = -3.09 (-0.49,+0.29), the peak energy Ep = 286 (-22,+21) keV, chi2 = 30/38 dof.

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

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