{
  "bibcode": "2022GCN.31544....1T",
  "body": "A. Tsvetkova, D. Frederiks, A.Lysenko, D. Svinkin,\nA. Ridnaia, M. Ulanov (all Ioffe), and A.Y. Lien (U Tampa), report:\n\nThe long GRB 211227A (Swift-BAT detection:\nBeardmore et al., GCN 31316; Lien et al., GCN 31326;\nMAXI/GSC detection: Tominaga et al., GCN 31319;\nCALET-GRBM detection: Cherry et al., GCN 31333),\nT0 (BAT) = 23:32:06.867, was detected by Konus-Wind (KW)\nin the waiting mode.\n\nA Bayesian block analysis of the KW waiting mode data in 25-400 keV range\nreveals two episodes with count rate excess >10 sigma over background.\nThe first one, lasting from ~T0-50 s to ~T0-10 s, is due to the solar\nactivity and is not associated with the GRB.\nThe second episode, from ~T0-1.5 s to ~T0+81 s, is consistent in time\nwith the BAT detection. It has a double-peaked structure,\nwith the first, narrow pulse peaking at ~T0, and the second,\nmore broad pulse - at ~T0 + 11 s.\n\nTo derive broad-band spectral parameters of this burst,\nwe performed a joint spectral analysis of the Swift/BAT data (15-150 keV)\nand the KW 3-channel spectral data (25-1700 keV).\n\nA fit to the time-averaged spectrum, measured from T0-1.540 s�� to \nT0+83.836 s,\nby the Band GRB function gives alpha = -1.34 (-0.08,+0.10),\nbeta = -2.26 (-1.11,+0.24), and Ep = 192 (-42,+45) keV; chi^2 = 48.5/ 57 \ndof.\n\nA fit to the spectrum near the peak KW count rate, measured from \nT0+10.236 s to T0+19.068 s,\nby the Band function gives alpha = -1.09 (-0.07,+0.08), beta = -2.29 \n(-0.11,+0.28),\nand Ep = 374 (-70,+66) keV; chi^2 = 47.1/58 dof.\n\nThe spectrum of the short initial pulse, measured from T0-1.540 s to \nT0+4.348 s,\nis well fit by a power law with an exponential cutoff (CPL), with\nalpha = -1.56 (-0.06,+0.15) and Ep = 366 (-179,+1201) keV; chi^2 = \n49.3/59 dof.\nAlthough the Band model fit to this spectrum is not constrained,\nfixing beta to the value -2.26, obtained for the time-integrated spectrum,\ngives alpha = -1.49 (-0.18, +0.24) and Ep = 240 (-116, +759) keV; chi^2 \n= 49.0/59 dof.\n\nIn the 15-1500 keV band, the total burst fluence is \n2.60(-0.21,+0.21)x10^-5 erg/cm^2,\nand the 64 ms peak energy flux is 2.0(-0.4,+0.4)x10^-6 erg/cm^2/s.\n\nAssuming the redshift z=0.228 (Malesani et al., GCN 31324)\nof the host galaxy candidate (Fu et al., GCN 31320),\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 isotropic energy release E_iso to 4.9(-0.4,+0,4)x10^51 erg,\nthe isotropic luminosity L_iso to 4.7(-1.0,+1,0)x10^50 erg/s,\nand the rest-frame peak energies of the time-integrated and peak spectra\nto 235(-51,+56) keV and 460 (-86, +81) keV, correspondingly.\nWith these values, GRB 211227A is consistent with the 90% prediction \nbands for the 'Amati'\nrelation and is an outlier in the 'Yonetoku' relation for the sample of�� \n >300 long KW GRBs\nwith known redshifts (Tsvetkova et al., 2021, ApJ, 908, 83).\nHowever, if we assume a higher burst redshift (z>0.5), GRB 211227A is \nconsistent\nwith both 'Amati' and 'Yonetoku' relations,\nsee http://www.ioffe.ru/LEA/GRBs/GRB211227A/GRB211227A_rest_frame.pdf\n\nAll the quoted errors are estimated at the 68% confidence level.\nAll the presented results are preliminary.\n\nThe KW light curve of this burst is available at \nhttp://www.ioffe.ru/LEA/GRBs/GRB211227A/",
  "circularId": 31544,
  "createdOn": 1643884363000,
  "email": "tsvetkova@mail.ioffe.ru",
  "subject": "GRB 211227A: Konus-Wind detection and joint Konus-Wind+Swift-BAT spectral analysis",
  "submitter": "Anastasia Tsvetkova at Ioffe Institute  <tsvetkova@mail.ioffe.ru>",
  "eventId": "GRB 211227A"
}