{
  "bibcode": "2020GCN.27596....1F",
  "body": "D. Frederiks, S. Golenetskii, R. Aptekar, A. Lysenko,\nA. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline,\non behalf of the Konus-Wind team, report:\n\nThe extremely-bright, short-duration GRB 200415A\n(IPN localization: Svinkin et al., GCN Circ. 27585, 27595;\nFermi-GBM observation: Bissaldi et al., GCN Circ. 27587)\ntriggered Konus-Wind at T0=31681.401 s UT (08:48:01.401).\n\nThe burst light curve starts at ~T0-2 ms with the sharp\nrise of extremely-bright pulse, with a duration of ~5 ms.\nThis pulse is followed by a weaker, steadily decaying\nemission which is visible up to ~T0+200 ms.\nThe emission is seen up to ~10 MeV.\n\nAs observed by Konus-Wind, the burst had a fluence of\n8.1(-0.8, +0.9)x10^-6 erg/cm2,\nand a 2-ms peak flux, measured from T0-0.002 s,\nof 1.0(-0.08,+0.08)x10^-3 erg/cm2/s\n(both in the 20 keV - 10 MeV energy range).\n\nThe time-integrated spectrum (measured from T0 to T0+0.192 s)\nis best fit in the 20 keV - 15 MeV range\nby a power law with exponential cutoff (CPL) model:\ndN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)\nwith  alpha = +0.10(-0.23,+0.27)\nand Ep = 818(-112,+136) keV (chi2 = 34/49 dof).\nFitting by a GRB (Band) model yields similar alpha and Ep,\nand an upper limit on the high energy photon index: beta < -2.5\n(chi2 =33/49 dof).\n\nThe spectrum measured near the peak count rate (from T0 to T0+0.064 s)\nis best fit in the 20 keV - 15 MeV range by the CPL model\nwith alpha = +0.12(-0.24,+0.20) and Ep = 1060(-160,+190) keV\n(chi2 = 25/36 dof). Fitting by a GRB (Band) model yields similar\nalpha and Ep, and an upper limit on the high energy photon index:\nbeta < -2.6 (chi2 =24/35 dof).\n\nAssuming the likely GRB 200415A association with the nearby Sculptor\ngalaxy at ~3.5 Mpc (Svinkin et al., GCN 27585, GCN 27595),\nwe estimate the burst isotropic energy to ~1.3x10^46 erg and\nthe 2-ms peak luminosity to ~1.6x10^48 erg/s.\nThese values closely resemble the energetics of the initial pulse of\nthe SGR 1806-20 giant magnetar flare (GF) measured by KW and HELICON\n(Frederiks et al., 2007 AstL 33 1).\n\nGRB 200415A also shows a striking similarity, in light curve, spectrum,\nand energy, with GRB 051103 (Frederiks et al., 2007 AstL 33 19),\nthe extragalactic GF candidate in the M81/M82 group of galaxies\nlocated at nearly the same distance, ~3.6 Mpc.\n\nEven the giant magnetar flare origin of GRB 200415A and GRB 051103\ncannot be established unequivocally (the key evidence, pulsating tail,\ncould hardly be detected by KW or Fermi-GBM from ~3.5 Mpc),\nthe common nature of the two ultra-bright flares is highly probable.\n\nThe Konus-Wind light curve of GRB 200415A is available at\nhttp://www.ioffe.ru/LEA/GRBs/GRB200415_T31681/\n\nA comparison of Konus-Wind light curves of GRB 200415A and GRB 051103\ncan be found at http://www.ioffe.ru/LEA/GRBs/GRB200415_T31681/051103_200415.pdf\n\n\nAll the quoted errors are at the 90% confidence level.\nAll the quoted values are preliminary.",
  "circularId": 27596,
  "createdOn": 1587055733000,
  "email": "fred@mail.ioffe.ru",
  "subject": "Konus-Wind observation of GRB 200415A (a magnetar Giant Flare in Sculptor Galaxy?)",
  "submitter": "Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>",
  "eventId": "GRB 200415A"
}