TITLE: GCN CIRCULAR NUMBER: 40631 SUBJECT: Konus-Wind detection of GRB 250601A DATE: 25/06/05 15:52:19 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 short-duration GRB 250601A (Fermi GBM detection: Fermi GBM team, GCN 40596; Sharma et al., GCN 40621; Swift/BAT-GUANO localization: DeLaunay et al., GCN 40600) triggered Konus-Wind at T0=62975.326 s UT (17:29:35.326).

The burst light curve shows a multi-peaked pulse, which starts at ~T0-0.5 s and has a total duration of ~0.8 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/GRB250601_T62975/

As observed by Konus-Wind, the burst had a fluence of 2.02(-0.28,+0.31)x10^-6 erg/cm2, and a 16-ms peak flux, measured from T0-0.004 s, of 7.00(-2.01,+2.06)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range).

Since the brightest peak of the burst light curve was detected before the trigger, the spectral analysis was performed using the KW 3-channel light curve data.

Modelling the KW 3-channel time-integrated spectrum (measured from T0-0.492 s to T0+0.276 s) by a power law with exponential cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), yields alpha = 0.31(-0.37,+0.52) and Ep = 436(-62,+76) keV.

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

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