{
  "subject": "Konus-Wind detection of GRB 250612C (short/hard with extended emission)",
  "bibcode": "2025GCN.40746....1F",
  "body": "D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,\nA. Tsvetkova,  M. Ulanov, and T. Cline,\non behalf of the Konus-Wind team, report:\n\nThe bright GRB 250612C (Fermi GBM detection: Fermi GBM team, GCN 40704;\nNeights & Meegan, GCN 40713; SVOM/GRM observation: Wang et al., GCN 40708;\nGRID detection: Yang et al., GCN 40732)\ntriggered Konus-Wind (KW) at T0=53591.512 s UT (14:53:11.512).\n\nThe burst light curve shows a very bright, multi-peaked emission episode,\nwhich starts at ~T0-0.05 s and has a duration of ~1.3 s.\nThis episode is followed by a much weaker extended emission tail visible to ~T0+25 s.\nThe emission is seen up to ~15 MeV.\n\nThe Konus-Wind light curve of this GRB is available at\nhttp://www.ioffe.ru/LEA/GRBs/GRB250612_T53591/\n\nAs observed by Konus-Wind, the burst had the total fluence\nof (6.92 ± 0.50)x10^-5 erg/cm^2 and a 16-ms peak energy flux,\nmeasured from T0+0.016, of (3.01 ± 0.38)x10^-4 erg/cm^2/s\n(both in the 20 keV - 10 MeV energy range).\n\nThe time-integrated spectrum of the initial episode (measured from T0 to T0+1.280 s)\nis best fit in the 20 keV - 20 MeV range by a power law with exponential\ncutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)\nwith  alpha = -0.90(-0.03,+0.02) and Ep = 2084 (-97,+103) keV (chi2 = 91.8/74 dof).\nFitting this spectrum by a Band function yields similar, within errors,\nvalues of alpha and Ep, and an upper limit on the high energy photon index beta\nof -4.0 (chi2 = 91.7/73 dof).\n\nThe spectrum near the peak count rate (measured from T0 to T0+0.064 s)\nis best fit in the 20 keV - 20 MeV range by a CPL model with\nalpha = -0.14(-0.13,+0.14) and Ep = 2073 (-214,+263) keV (chi2 = 38.7/35 dof).\nFitting this spectrum by a Band function yields the same values of alpha and Ep,\nand an upper limit on the high energy photon index beta of -2.0 (chi2 = 38.4/34 dof).\n\nThe spectrum of the extended emission, measured from T0+1.280 s to T0+25.856 s,\nis best fit in the 20 keV - 20 MeV range by a simple power law (PL) function with\nthe photon PL index of -1.68 ± 0.12.\n\n\nAll the quoted errors are estimated at the 68% confidence level.\nAll the presented results are preliminary.\n",
  "submittedHow": "email",
  "circularId": 40746,
  "eventId": "GRB 250612C",
  "createdOn": 1750073612376,
  "submitter": "Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>"
}