{
  "bibcode": "2021GCN.30276....1S",
  "body": "D. Svinkin, S. Golenetskii, D. Frederiks, M. Ulanov,\nA. Tsvetkova, A. Lysenko, A. Ridnaia, and T. Cline\non behalf of the Konus-Wind team, report:\n\nThe very bright, long-duration GRB 210619B\n(Swift-BAT detection: D'Avanzo et al., GCN Circ. 30261;\nGECAM detection: Zhao et al., GCN Circ. 30264;\nFermi-LAT detection: Axelsson et al., GCN Circ. 30270)\ntriggered Konus-Wind at T0=86368.157 s UT (23:59:28.157).\n\nThe burst light curve shows a bright hard initial episode,\nwhich starts at ~T0 and has a duration of ~10 s,\nfollowed by weaker pulses. The total burst duration is ~80 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/GRB210619_T86368/\n\nAs observed by Konus-Wind, the burst\nhad a fluence of 4.60(-0.13,+0.13)x10^-4 erg/cm2,\nand a 64-ms peak flux, measured from T0+0.640 s,\nof 1.54(-0.12,+0.12)x10^-4 erg/cm2/s\n(both in the 20 keV - 10 MeV energy range).\n\nThe time-averaged spectrum of the burst\n(measured from T0 to T0+66.816 s)\nis best fit in the 20 keV - 15 MeV range\nby the GRB (Band) model with the following parameters:\nthe low-energy photon index alpha = -1.02(-0.03,+0.04),\nthe high energy photon index beta = -2.10(-0.04,+0.03),\nthe peak energy Ep = 261(-13,+14) keV\n(chi2 = 118/96 dof).\n\nThe spectrum near the maximum count rate\n(measured from T0+0.512 to T0+0.768 s)\nis best fit in the 20 keV - 15 MeV range\nby the GRB (Band) model with the following parameters:\nthe low-energy photon index alpha = -0.41(-0.11,+0.12),\nthe high energy photon index beta = -2.06(-0.12,+0.09),\nthe peak energy Ep = 572(-81,+98) keV\n(chi2 = 76/60 dof).\n\nAssuming the redshift z=1.937\n(de Ugarte Postigo et al., GCN Circ. 30272)\nand a standard cosmology model with H_0 = 67.3 km/s/Mpc,\nOmega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014),\nwe estimate the following rest-frame parameters:\nthe isotropic energy release E_iso is 4.41(-0.12,+0.12)x10^54 erg,\nthe peak luminosity L_iso is 4.34(-0.34,+0.34)x10^54 erg/s,\nthe rest-frame peak energy of the time-integrated spectrum,\nEp,i,z, is 767(-38,+41) keV, and the rest-frame peak energy of\nthe 'peak' spectrum, Ep,p,z, is 1680(-238,+288) keV.\nWith these energetics, the burst lies within the 90% prediction bands\nfor both 'Amati' and 'Yonetoku' relations built for the sample\nof 138 long KW GRBs with known redshifts\n(Tsvetkova et al., ApJ 850 161, 2017),\nsee http://www.ioffe.ru/LEA/GRBs/GRB210619_T86368/GRB210619B_rest_frame.pdf.\n\nAmong the KW GRB sample, GRB 210619B is within top 4% in the terms\nof E_iso and have L_iso comparable to the most luminous GRB 110918A \n(Frederiks et al., ApJ 779, 151, 2013).\n\nAll the quoted errors are at the 90% confidence level.\nAll the quoted values are preliminary.",
  "circularId": 30276,
  "createdOn": 1624204585000,
  "email": "svinkin@mail.ioffe.ru",
  "subject": "Konus-Wind detection of GRB 210619B",
  "submitter": "Dmitry Svinkin at Ioffe Institute  <svinkin@mail.ioffe.ru>",
  "eventId": "GRB 210619B"
}