TITLE: GCN CIRCULAR NUMBER: 39590 SUBJECT: Konus-Wind detection of GRB 250222A DATE: 25/03/04 13:35:08 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 250222A (SVOM-GRM detection: Wang et al., GCN 39454; IPN triangulation: Svinkin et al., GCN 39588) triggered Konus-Wind (KW) at T0=51862.905 s UT (14:24:22.905).

The burst light curve shows a bright, multi-peaked pulse, with the duration of ~2.5 s, followed by a weaker, decaying emission. The total duration of the burst is ~13 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/GRB250222_T51862/

As observed by Konus-Wind, the burst had a fluence of (1.79 ± 0.19)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0 + 0.064 s, of (1.53 ± 0.20)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+16.640 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 = -0.51 (-0.22,+0.26), the high energy photon index beta = -2.28 (-0.14,+0.11), the peak energy Ep = 173 (-21,+23) keV, chi2 = 98/97 dof.

The spectrum near the peak count rate (measured from T0 to T0+0.256 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 = 0.40 (-0.61,+1.09), the high energy photon index beta = -1.97 (-0.13,+0.10), the peak energy Ep = 169 (-39,+46) keV, chi2 = 42/43 dof.

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

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