{
  "bibcode": "2025GCN.41027....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\nWe report on a further analysis of the KW detection\nof the very bright, long-duration GRB 250706C\n(Frederiks et al., GCN 41013), which common origin with\nthe SVOM/ECLAIRs GRB 250706B (Palmerio et al., GCN 40989)\nwas confirmed from the FERMI/LAT observation (Longo et al., GCN 41019).\n\nGRB 250706C triggered Konus-Wind (KW) at T0=60322.626 s UT (16:45:22.626),\n~1200 s before the SVOM/ECLAIRs trigger on GRB 250706B.\nThe burst light curve shows a very bright, multi-peaked\nemission pulse with the duration of ~50 s (20-1500 keV).\nThis pulse is followed by a weaker, smoothly decaying emission tail,\nvisible up to the end of the KW triggered data record (~T0+250 s).\nThe emission in the main pulse is seen up to ~15 MeV.\n\nThe KW light curve is available at\nhttp://www.ioffe.ru/LEA/GRBs/GRB250706_T60322/\n\nAs observed by Konus-Wind, the burst had\nthe total fluence of (5.12 ± 0.06)x10^-4 erg/cm^2 and\na 16-ms peak energy flux, measured from T0 + 36.800 s,\nof (4.16 ± 0.22)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).\n\nThe time-integrated spectrum (measured from T0 to T0+51.968 s)\nis best fit in the 20 keV - 15 MeV range by a GRB (Band) function\nwith the following model parameters:\nthe low-energy photon index alpha = -1.00 (-0.01,+0.01),\nthe high energy photon index beta = -3.65 (-0.44,+0.23),\nthe peak energy Ep = 850(-15,+15) keV,\nchi2 = 125/96 dof.\n\nThe spectrum near the peak count rate (measured from T0+36.608 s to T0+37.120 s)\nis best fit in the 20 keV - 15 MeV range by a GRB (Band) function\nwith the following model parameters:\nthe low-energy photon index alpha = -1.10 (-0.04,+0.04),\nthe high energy photon index beta = -2.91 (-0.60,+0.30),\nthe peak energy Ep = 1005(-91,+104) keV,\nchi2 = 69/58 dof.\n\nThe spectrum of the decaying tail (measured from T0+51.968 s to T0+232.192)\nis best fit by a simple power law (PL) function with the PL photon index\nof (-2.0 ± 0.06), chi2 = 92/99 dof.\n\nAssuming the redshift z=0.942 (Palmerio et al., GCN 41022)\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 (1.26 ± 0.02)x10^54 erg,\nthe isotropic peak luminosity L_iso to (2.00 ± 0.11)x10^53 erg/s, and\nthe rest-frame peak spectral energy Epi,z to 1650(-30,+30) keV.\nWith the obtained estimates, GRB 250706B/C is consistent with 68% prediction bands\nof both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs\nwith known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021),\nsee http://www.ioffe.ru/LEA/GRBs/GRB250706_T60322/GRB250706BC_rest_frame.pdf\n\nAll the quoted errors are estimated at the 68% confidence level.\nAll the presented results are preliminary.\n",
  "eventId": "GRB 250706B",
  "submitter": "Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>",
  "createdOn": 1751982905449,
  "submittedHow": "email",
  "subject": "GRB 250706B/C: Konus-Wind analysis of the prompt emission",
  "circularId": 41027
}