TITLE: GCN CIRCULAR NUMBER: 38954 SUBJECT: Konus-Wind detection of GRB 250113A DATE: 25/01/15 13:54:39 GMT FROM: Anna Ridnaia at Ioffe Institute ridnaia@mail.ioffe.ru

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 250113A (SVOM/GRM observation: Wang et al., GCN 38923; INTEGRAL/SPI-ACS detection: Barria et al., GCN 38935; IPN triangulation: Kozyrev et al., GCN 38953) triggered Konus-Wind at T0=23073.686 s UT (06:24:33.686).

The burst light curve shows a multipeaked structure which starts at ~T0-3.0 s and has a total duration of ~46.8 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/GRB250113_T23073/

As observed by Konus-Wind, the burst had a fluence of 3.88(-0.13,+0.14)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+0.656 s, of 6.12(-1.01,+1.03)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+49.408 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 = -1.42(-0.05,+0.05) and Ep = 251(-18,+21) keV (chi2 = 75/88 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.5 (chi2 = 75/87 dof).

The spectrum near the maximum count rate (measured from T0+0.256 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.19(-0.16,+0.19), the high energy photon index beta = -2.49(-0.27,+0.18), the peak energy Ep = 321(-30,+31) keV (chi2 = 59/74 dof).

All the quoted errors are at the 68% confidence level. All the quoted values are preliminary.

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