TITLE: GCN CIRCULAR NUMBER: 41295 SUBJECT: Konus-Wind detection of GRB 250807A DATE: 25/08/08 18:25:17 GMT FROM: Dmitry Svinkin at Ioffe Institute svinkin@mail.ioffe.ru

D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report:

The long-duration GRB 250807A (Swift-BAT detection: Klingler et al., GCN 41262; AstroSat-CZTI detection: Salunke et al., GCN 41281; SVOM-GRM detection: Wang et al., GCN 41283) triggered Konus-Wind at T0=38766.990 s UT (10:46:06.990).

The burst light curve shows a multipeaked structure which starts at ~T0-2.3 s and has a total duration of ~79 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/GRB250807_T38766/

As observed by Konus-Wind, the burst had the total fluence of 1.03(-0.09,+0.08)x10^-4 erg/cm2, and the 64-ms peak flux, measured from T0+35.904 s, of 1.11(-0.10,+0.10)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+79.104 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 = -1.04(-0.04,+0.04), the high energy photon index beta = -2.74(-0.66,+0.26), the peak energy Ep = 369(-26,+26) keV (chi2 = 132/97 dof).

The spectrum near the maximum count rate (measured from T0+29.952 to T0+38.144 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 = -1.04(-0.05,+0.05) and Ep = 390(-25,+28) keV (chi2 = 105/86 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.5 (chi2 = 105/85 dof).

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

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