{
  "bibcode": "2025GCN.41957....1P",
  "eventId": "GRB 250920C",
  "circularId": 41957,
  "subject": "Konus-Wind detection of GRB 250920C",
  "submittedHow": "web",
  "format": "text/plain",
  "submitter": "Valentina Panteleeva at Ioffe Institute <panteleevav228@gmail.com>",
  "createdOn": 1758654758801,
  "body": "V. Panteleeva, 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-duration GRB 250920C (Fermi-GBM detection:\nThe Fermi GBM team, GCN 41903; Mailyan & Meegan, GCN 41917;\nSwift-BAT detection: Gupta et al., GCN 41904; Gupta et al., GCN 41924; \nSVOM-GRM observaion: Wang et al., GCN 41929)\ntriggered Konus-Wind at T0=55519.312 s UT (15:25:19.312).\n\nThe burst light curve shows a multipeaked structure\nwhich starts at ~T0-0.4 s and has a total duration of ~41 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/GRB250920_T55519/\n\nAs observed by Konus-Wind, the burst\nhad the total fluence of 2.91(-0.21,+0.29)x10^-5 erg/cm2,\nand the 64-ms peak flux, measured from T0+25.904 s,\nof 8.27(-0.78,+0.78)x10^-6 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+41.216 s)\nis best fit in the 20 keV - 10 MeV range\nby the GRB (Band) model with the following parameters:\nthe low-energy photon index alpha = -1.22(-0.07,+0.09),\nthe high energy photon index beta = -3.19(-6.81,+0.51),\nthe peak energy Ep = 160(-12,+9) keV\n(chi2 = 104/97 dof).\n\nThe spectrum near the maximum count rate\n(measured from T0+24.832 to T0+33.024 s)\nis best fit in the 20 keV - 10 MeV range\nby a power law with exponential cutoff model:\ndN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)\nwith alpha = -1.14(-0.07,+0.07)\nand Ep = 220(-14,+16) keV (chi2 = 96/81 dof).\nFitting by a GRB (Band) model yields the same alpha and Ep,\nand an upper limit on the high energy photon index: beta < -3.15\n(chi2 = 97/80 dof).\n\nAssuming the redshift z=1.399 (Sanchez-Ramirez et al., GCN 41928;\nIzzo et al., GCN 41955)\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 following rest-frame parameters:\nthe isotropic energy release E_iso is 1.54(-0.11,+0.16)x10^53 erg,\nthe peak luminosity L_iso is 1.05(-0.10,+0.10)x10^53 erg/s,\nthe rest-frame peak energy of the time-averaged spectrum\nEp,i,z is 383(-30,+22) keV and the spectrum near the maximum count rate\nEp,p,z is 528(-33,+38) keV.\n\nWith the obtained estimates, GRB 250920C is inside 68% prediction bands for\nboth the 'Amati' and the 'Yonetoku' relations derived for the sample of >300 long\nKW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021),\nsee http://www.ioffe.ru/LEA/GRBs/GRB250920_T55519/GRB250920C_rest_frame.pdf\n\nAll the quoted errors are at the 68% confidence level.\nAll the quoted values are preliminary."
}