{
  "submitter": "Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>",
  "subject": "Konus-Wind detection of GRB 230818A",
  "circularId": 34511,
  "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 long GRB 230818A (Swift detection: Tohuvavohu et al., GCN 34479;\nFermi GBM observation: Veres et al., GCN 34501)\ntriggered Konus-Wind (KW) at T0=84458.443 s UT (23:27:38.443).\n\nThe burst light curve shows a single FRED-like pulse\nwhich starts at ~T0-0.256 s and has a duration of ~10 s.\nThe emission is seen up to ~2 MeV.\n\nThe Konus-Wind light curve of this GRB is available at\nhttp://www.ioffe.ru/LEA/GRBs/GRB230818_T84458/\n\nAs observed by Konus-Wind, the burst had\na total fluence of (4.91 ± 1.76)x10^-6 erg/cm^2 and\na 64-ms peak energy flux, measured from T0,\nof (3.08 ± 0.90)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).\n\nThe time-integrated spectrum of the burst (measured from T0 to T0+16.640 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 = -1.00(-0.23,+0.27) and Ep = 251(-49,+81) keV (chi2 = 91/98 dof).\nFitting this spectrum by a Band function yields the same values of alpha and Ep,\nand an upper limit on the high energy photon index beta of -2.5 (chi2 = 91/97 dof).\n\nThe spectrum near the peak count rate (measured from T0 to T0+0.256 s)\nis best fit in the 20 keV - 15 MeV range by a CPL model\nwith alpha = -0.40(-0.44,+0.56) and Ep = 259(-45,+64) keV (chi2 = 18/17 dof).\nFitting this spectrum by a Band function yields the same values of alpha and Ep,\nand an upper limit on the high energy photon index beta of -2.7 (chi2 = 18/16 dof).\n\nAssuming the redshift z=2.42 (Malesani et al., GCN 34485)\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 (6.95 ± 2.49)x10^52 erg,\nthe isotropic peak luminosity L_iso to (1.49 ± 0.44)x10^53 erg/s,\nthe rest-frame peak energy of the time-integrated spectrum Ep,i,z to ~860 keV,\nand the rest-frame peak energy at the peak of the emission Ep,p,z to ~890 keV.\nWith the obtained estimates, GRB 230818A is inside 90% prediction band for\nthe 'Amati' relation and inside 68% prediction band for the 'Yonetoku' relation\nderived for the sample of >300 long KW GRBs with known redshifts\n(Tsvetkova et al., 2017; Tsvetkova et al., 2021), see\nhttp://www.ioffe.ru/LEA/GRBs/GRB230818_T84458/GRB230818A_rest_frame.pdf\n\nAll the quoted errors are estimated at the 68% confidence level.\nAll the presented results are preliminary.\n\n",
  "bibcode": "2023GCN.34511....1F",
  "eventId": "GRB 230818A",
  "submittedHow": "email-legacy",
  "createdOn": 1692631015531
}