TITLE: GCN CIRCULAR NUMBER: 40453 SUBJECT: Konus-Wind detection of GRB 250506A DATE: 25/05/13 10:36:33 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 250506A (Fermi-GBM detection: The Fermi GBM team, GCN 40355; SVOM detection: Wang et al., GCN 40358; GECAM-B detection: Wang et al., GCN 40396; GRBAlpha detection: Pal et al., GCN 40440;) triggered Konus-Wind at T0=08605.817 s UT (02:23:25.817).
The burst light curve shows a multi-peaked structure which starts at ~T0-2.1 s and has a total duration of ~56 s. The emission is seen up to ~7 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250506_T08605
As observed by Konus-Wind, the burst had a fluence of 2.41(-0.16,+0.38)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+33.728 s, of 8.39(-0.74,+0.75)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+57.600 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 = -1.06(-0.04,+0.08), the high energy photon index beta = -3.51(-6.49,+0.91), the peak energy Ep = 284(-28,+28) keV (chi2 = 123/97 dof).
The spectrum near the maximum count rate (measured from T0+33.024 to T0+41.216 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 = -1.02(-0.07,+0.08) and Ep = 278(-21,+25) keV (chi2 = 111/98 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.0 (chi2 = 111/97 dof).
All the quoted errors are at the 68% confidence level. All the quoted values are preliminary.
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