{
  "bibcode": "2022GCN.32668....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 extraordinary bright GRB 221009A\n(Fermi-GBM detection: Veres et al. GCN Circ 32636, Lesage et al. GCN Circ 32642;\nFermi-LAT detection: Bissaldi et al. GCN Circ 32637;\nIPN triangulation: Svinkin et al. GCN Circ 32641;\nAGILE/MCAL detection detection: Ursi et al., GCN Circ 32650)\ntriggered Konus-Wind (KW) at T0=47821.648 s UT (13:17:01.648).\n\nThe burst light curve starts with a FRED-like initial pulse (IP)\nthat lasts from ~T0-1 s to ~T0+25 s. The IP is followed by an extremely\nbright multi-peaked emission in the interval from ~T0+170 s to ~T0+600 s,\nwhere a preliminary-estimated count rate reaches several hundred counts/s.\nThe emission at this stage is seen up to at least ~15 MeV.\nThe pulsed phase of the burst evolves to a steadily decaying emission tail,\nwhich is visible in the KW data for more than 10000 s.\n\nThe preliminary Konus-Wind light curve of this GRB is available at\nhttp://www.ioffe.ru/LEA/GRBs/GRB221009_T47821/\n\nA time-averaged spectrum of the IP (measured from T0 to T0+28.842 s)\nis best fit in the 20 keV - 15 MeV range by a power law with exponential\ncutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)\nwith  alpha = -1.62(-0.04,+0.05) and Ep = 975(-332,+712) keV (chi2 = 80/98 dof).\nThe fluence in this time interval is estimated to (2.4 �� 0.3)x10^-05 erg/cm^2\nand a 64-ms peak energy flux, measured from T0 + 5.760 s,\nto (6.2 �� 0.7)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).\n\nA time-averaged spectrum at the onset of the brightest phase of the event\n(measured from T0+180.48 to T0+200.064 s) is best fit in the 20 keV - 15 MeV range\nby a GRB (Band) function with the following model parameters:\nthe low-energy photon index alpha = -1.09 (-0.01,+0.01),\nthe high energy photon index beta = -2.60 (-0.06,+0.06),\nthe peak energy Ep = 1060 (-30,+31) keV, chi2 = 161/97 dof.\nThe fluence in this time interval is estimated to (8.8 �� 0.1)x10^-04 erg/cm^2\n\nThe brightness of the main burst episode doesn't allow to perform\nthe standard KW spectral analysis of the emission at this stage of the event.\nHowever, using the latter spectrum and a count rate light curve in the 80-320 keV range\nwith preliminary dead-time corrections applied, we obtain a rough estimate\nof the fluence of the event in the interval from T0 to T0+600 s of ~0.052 erg/cm^2,\nwhich is the highest value observed for GRBs for almost 28 years of the KW operation.\nFurther analysis of this extraordinary event is ongoing and\nthe results will be reported eslsewhere.\n\nAssuming the redshift z=0.151 (de Ugarte Postigo et al., GCN 32648)\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 burst isotropic energy release E_iso to a high,\nbut reasonable value of ~3.0x10^54 erg.\nThe rest-frame peak energy of the spectrum Ep,z is estimated to ~1150 keV.\nWith these preliminary values, GRB 221009A perfectly fits the\n'Amati' relation for the sample of >300 long KW GRBs with known redshifts\n(Tsvetkova et al., 2017; Tsvetkova et al., 2021),\nsee http://www.ioffe.ru/LEA/GRBs/GRB221009_T47821/GRB221009A_rest_frame.pdf\n\nAll the quoted errors are at the 68% confidence level.\nAll the presented results are preliminary.",
  "circularId": 32668,
  "createdOn": 1665433089000,
  "email": "fred@mail.ioffe.ru",
  "subject": "Konus-Wind detection of GRB 221009A",
  "submitter": "Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>",
  "eventId": "GRB 221009A"
}