{
  "eventType": [
    "GRB",
    "Gamma-ray Transient"
  ],
  "createdOn": 1790257173009,
  "circularId": 45722,
  "submittedHow": "web",
  "subject": "Konus-Wind detection of GRB 260921A (possible merger-origin)",
  "format": "text/plain",
  "eventId": "GRB 260921A",
  "submitter": "Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>",
  "body": "A. Ridnaia, D. Frederiks, A. Lysenko, V. Panteleeva,\nD. Svinkin, A. Tsvetkova,  M. Ulanov, and T. Cline,\non behalf of the Konus-Wind team, report:\n\nThe long-duration GRB 260921A\n(Fermi-GBM detection: Fermi GBM Team, GCN 45674;\nSonawane, GCN 45684;\nSwift-BAT detection: Page et al., GCN 45676;\nParsotan et al., GCN 45686;\nAstroSat-CZTI detection: Goyal et al., GCN 45687)\ntriggered Konus-Wind at T0=34147.045 s UT (09:29:07.045).\n\nThe burst light curve shows a multipeaked structure\nwhich starts at ~T0-2.8 s and has a total duration of ~8.9 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/GRB260921_T34147/\n\nAs observed by Konus-Wind, the burst\nhad the total fluence of 7.93(-0.60,+0.68)x10^-6 erg/cm2,\nand the 64-ms peak flux, measured from T0+2.880 s,\nof 3.71(-0.70,+0.73)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+8.448 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 = -0.92(-0.18,+0.21)\nand Ep = 334(-43,+59) keV (chi2 = 78/82 dof).\nFitting by a GRB (Band) model yields the same alpha and Ep,\nand an upper limit on the high energy photon index: beta < -2.3\n(chi2 = 79/81 dof).\n\nThe spectrum near the maximum count rate\n(measured from T0+0.256 to T0+8.448 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 = -0.90(-0.21,+0.24)\nand Ep = 308(-41,+59) keV (chi2 = 80/83 dof).\nFitting by a GRB (Band) model yields the same alpha and Ep,\nand an upper limit on the high energy photon index: beta < -2.3\n(chi2 = 80/82 dof).\n\nAssuming the redshift z=1.300 (Segura et al., GCN 45678)\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 3.65(-0.27,+0.31)x10^52 erg,\nthe peak luminosity L_iso is 3.93(-0.74,+0.77)x10^52 erg/s,\nthe rest-frame peak energy of the time-averaged spectrum\nEp,i,z is 768(-99,+136) keV and the spectrum near the maximum count rate\nEp,p,z is 708(-95,+135) keV.\n\nWith the obtained estimates, GRB 260921A is a clear outlier\nin the 'Amati' relation and nearly an outlier in the 'Yonetoku'\nrelation derived for the sample of >300 long KW GRBs with known redshifts\n(Tsvetkova et al., 2017; Tsvetkova et al., 2021), but is generally consistent \nwith the Type I (merger-origin) population,\nsee http://www.ioffe.ru/LEA/GRBs/GRB260921_T34147/GRB260921A_rest_frame.pdf\n\nAll the quoted errors are at the 68% confidence level.\nAll the quoted values are preliminary."
}