TITLE: GCN CIRCULAR NUMBER: 40746 SUBJECT: Konus-Wind detection of GRB 250612C (short/hard with extended emission) DATE: 25/06/16 11:33:32 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 bright GRB 250612C (Fermi GBM detection: Fermi GBM team, GCN 40704; Neights & Meegan, GCN 40713; SVOM/GRM observation: Wang et al., GCN 40708; GRID detection: Yang et al., GCN 40732) triggered Konus-Wind (KW) at T0=53591.512 s UT (14:53:11.512).
The burst light curve shows a very bright, multi-peaked emission episode, which starts at ~T0-0.05 s and has a duration of ~1.3 s. This episode is followed by a much weaker extended emission tail visible to ~T0+25 s. The emission is seen up to ~15 MeV.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250612_T53591/
As observed by Konus-Wind, the burst had the total fluence of (6.92 ± 0.50)x10^-5 erg/cm^2 and a 16-ms peak energy flux, measured from T0+0.016, of (3.01 ± 0.38)x10^-4 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum of the initial episode (measured from T0 to T0+1.280 s) is best fit in the 20 keV - 20 MeV range by a power law with exponential cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.90(-0.03,+0.02) and Ep = 2084 (-97,+103) keV (chi2 = 91.8/74 dof). Fitting this spectrum by a Band function yields similar, within errors, values of alpha and Ep, and an upper limit on the high energy photon index beta of -4.0 (chi2 = 91.7/73 dof).
The spectrum near the peak count rate (measured from T0 to T0+0.064 s) is best fit in the 20 keV - 20 MeV range by a CPL model with alpha = -0.14(-0.13,+0.14) and Ep = 2073 (-214,+263) keV (chi2 = 38.7/35 dof). Fitting this spectrum by a Band function yields the same values of alpha and Ep, and an upper limit on the high energy photon index beta of -2.0 (chi2 = 38.4/34 dof).
The spectrum of the extended emission, measured from T0+1.280 s to T0+25.856 s, is best fit in the 20 keV - 20 MeV range by a simple power law (PL) function with the photon PL index of -1.68 ± 0.12.
All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary.
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