{
  "bibcode": "2021GCN.29415....1F",
  "body": "D. Frederiks, S. Golenetskii, A.Lysenko, A. Ridnaia,\nD. Svinkin, A. Tsvetkova,  M. Ulanov, and T. Cline,\non behalf of the Konus-Wind team, report:\n\nThe long GRB 210204A (Fermi GBM detection:  Bissaldi, GCN 29393;\nGECAM detection: Li et al, GCN 29392;\nIPN triangulation: Hurley et al., GCN 24908;\nAstroSat CZTI Detection: Waratkar et al., GCN 29410),\nassociated with the fast optical transient ZTF21aagwbjr/AT2021buv\n(Kool et al., GCN 29405),\ntriggered Konus-Wind (KW) at T0=23570.576 s UT (06:32:50.576).\n\nThe burst light shows a bright, multi-peaked pulse, which starts\nat ~T0-30 s and has a duration of ~80 s.\nA weaker precursor is clearly visible in the KW waiting\nmode data around ~T0-165 s.\nThe emission in the main pulse is seen up to ~3 MeV.\n\nThe Konus-Wind light curve of this GRB is available at\nhttp://www.ioffe.ru/LEA/GRBs/GRB210204_T23570/\n\nAs observed by Konus-Wind, the burst had\na fluence of (5.7 �� 0.9)x10^-5 erg/cm^2 and\na 64-ms peak energy flux, measured from T0+2.304,\nof (5.0 �� 0.7)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).\n\nThe time-integrated spectrum (measured from T0 to T0+49.408 s)\nis best fit in the 20 keV - 20 MeV range\nby the GRB (Band) function with the following model parameters:\nthe low-energy photon index alpha = -1.04 (-0.12,+0.18),\nthe high energy photon index beta = -2.43 (-0.18,+0.31),\nthe peak energy Ep = 137 (-25,+22) keV,\nchi2 = 79/97 dof.\n\nThe spectrum near the peak count rate (measured from T0\nto T0+8.448 s) is best fit in the 20 keV - 20 MeV range\nby the GRB (Band) function with the following model parameters:\nthe low-energy photon index alpha = -0.28 (-0.54,+0.64),\nthe high energy photon index beta = -2.12 (-0.24,+0.11),\nthe peak energy Ep = 123 (-24,+49) keV,\nchi2 = 109/97 dof.\n\nAssuming the redshift z=1.466 (Izzo et al., GCN 29411)\nand a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315,\nand Omega_Lambda = 0.685 (Planck Collaboration, 2014),\nwe estimate the isotropic energy release E_iso to ~2.3x10^53 erg,\nthe isotropic luminosity L_iso to ~7.1x10^52 erg/s,\nand the rest-frame peak energy of the time-integrated spectrum Ep,z to ~340 keV.\nWith these values, GRB 210204A is within 68% prediction bands\nfor both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs\nwith known redshifts (Tsvetkova et al., ApJ, in press),\nsee http://www.ioffe.ru/LEA/GRBs/GRB210204_T23570/GRB210204A_rest_frame.pdf\n\n\n\nAll the quoted errors are estimated at the 90% confidence level.\nAll the presented results are preliminary.",
  "circularId": 29415,
  "createdOn": 1612708060000,
  "email": "fred@mail.ioffe.ru",
  "subject": "Konus-Wind detection of GRB 210204A / ZTF21aagwbjr",
  "submitter": "Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>",
  "eventId": "GRB 210204A"
}