{
  "bibcode": "2013GCN.14487....1G",
  "body": "S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, V. Pal'shin,\nP. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf\nof the Konus-Wind team, report:\n\nThe long extremely intense GRB 130427A (Swift-BAT trigger #554620:\nMaselli et al., GCN 14448; Barthelmy et al., GCN 14470;\nFermi-LAT detection: Zhu et al., GCN 14471;\nFermi-GBM observation: von Kienlin, GCN 14473;\nSPI-ACS/INTEGRAL observations: Pozanenko et al., GCN 14484)\ntriggered Konus-Wind (K-W) at T0=28029.501s UT (07:47:09.501)\n~50 s before the BAT trigger.\n\nThe K-W light curve shows a huge mult-peaked emission complex\nstarted at ~T0, peaked at ~T0+8 s, and having a duration of ~20 s.\nThe emission is seen up to ~12 Mev.\nThis extremely bright phase of the event passes into a weaker decaying\ntail out to ~T0+120s, when the second emission episode started.\nIt shows a FRED-like pulse, ~100 times weaker in a peak count\nrate than the initial complex.\nThe decaying emission is detectable by K-W in the 20-1200 keV band\nout to ~T0+250s, when the instrument switched into the data readout mode.\n\nThe Konus-Wind light curve of this GRB is available at\nhttp://www.ioffe.ru/LEA/GRBs/GRB130427_T28029/\n\nAs observed by Konus-Wind, the main phase of the burst had\na fluence of (2.68 � 0.01)x10^-3 erg/cm2 and a 16-ms peak flux,\nmeasured from T0+7.774 s, of (6.9 � 0.1)x10^-4 erg/cm2/s\n(both in the 20 - 1200 keV energy range).\nThe fluence of GRB 130427A is the highest observed by K-W\nfor ~18 years of GRB observations and its peak flux\nis only ~30% lower than measured by K-W for the\nultra-luminous GRB 110918A.\n\nThe time-averaged spectrum of the main phase of the burst\n(measured from T0 to T0+18.688 s) is best fit in the 20 keV-15 MeV range\nby the GRB (Band) function with the following model parameters:\nthe low-energy photon index alpha = -0.958 � 0.006,\nthe high energy photon index beta = -4.17 � 0.16,\nthe peak energy Ep = 1028 � 8 keV,\nchi2 = 124/96 dof.\n\nThe spectrum at the maximum count rate (measured from T0+7.680 to T0+7.936 s)\nis best fit in the 20 keV - 15 MeV range\nby a power law with exponential cutoff model, for which:\nthe photon index alpha = -0.57 � 0.02, and\nthe peak energy Ep = 1213 � 31 keV,\nchi2 = 63/84 dof.\n\nModelling the 3-channel time-averaged spectrum\nof the second emission episode (from T0+120 s to T0+250 s)\nby a power law with exponential cutoff model\nyiels the photon index alpha~-1.6 and\nthe peak energy Ep ~ 240 keV.\nThe 20-1200 keV energy fluence measured at this\nphase of the event is ~9x10^-5 erg/cm2.\n\nAssuming z=0.34 (Levan et al., GCN 14455; Xu et al. GCN 14478)\nand a standard cosmology model with H_0 = 70 km/s/Mpc,\nOmega_M = 0.27, and Omega_Lambda = 0.73,\nthe isotropic energy release E_iso is ~8.5x10^53 erg,\nand the peak luminosity (L_iso)_max is ~2.7x10^53 erg/s.\n\nAll the quoted errors are estimated at the 1 sigma confidence level.",
  "circularId": 14487,
  "createdOn": 1367144570000,
  "email": "fred@mail.ioffe.ru",
  "subject": "Konus-Wind observation of GRB 130427A",
  "submitter": "Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>",
  "eventId": "GRB 130427A"
}