{
  "bibcode": "2022GCN.32819....1M",
  "body": "P. Minaev (IKI), A. Pozanenko (IKI), I. Chelovekov (IKI) report on \nbehalf of GRB IKI FuN:\n\nWe analyze the first episode of GRB 221009A (Dichiara et al., GCN 32632; \nKennea and Williams, GCN  32635; Veres et al., GCN 32636; Bissaldi et \nal., GCN  32636; Svinkin et al., GCN 32641; Piano et al., GCN 32657; \nPillera et al., GCN 32658;  Gotz et al., GCN 32660; Xiao et al., GCN \n32661; Frederiks et al., GCN 32668; GCN 32668; Ripa et al., GCN 32685; \nKozyrev et al., GCN 32805) not affected by dead time and pile-up \ninstrumental effects, using publicly available data of GBM/Fermi and \nSPI-ACS/INTEGRAL.\n\nWe investigate energy spectrum of the time interval (T0-1, T0+55) s, \nwhere T0 = 13:16:59 UTC 2022-10-09 is a time of  GBM/Fermi trigger.  The \nspectrum can be fitted by a simple power law model with the spectral \nindex of gamma = -1.68 +/- 0.01.\n\nSee the spectrum in http://grb.rssi.ru/GRB221009A/GRB221009A_1st_episode.png\n\nIt is in a contradiction with CPL (power law with exponential cutoff) \nspectral model for the episode, obtained by Lesage et al., GCN 32642 \nusing GBM/Fermi data (Epeak = 375 +/- 87 keV) and by Frederiks et al., \nGCN 32668 using Konus/WIND data (Epeak = 975 (-332, +712) keV). The \nvalue of spectral index is not typical for indexes before the break (in \nCPL or Band model), but it is a rather typical for the index after the \nbreak in Band model. We hypothesize the actual break to be placed at low \nenergies (Epeak < 20 keV). The hypothesis could be supported by placing \nEiso parameter into Amati correlation diagram.   The Eiso = (3.2 +/- \n0.1)E51 erg is calculated  within our power law model with gamma = -1.68 \nand using redshift value of z = 0.151 (de Ugarte Postigo et al., GCN \n32648; Castro-Tirado et al., GCN 32686). The Eiso value corresponds to 2 \nsigma range of possible Epeak value of (20, 315) keV for type II (long) \nGRBs (Minaev et al., MNRAS, 492, 2, 1919, 2020).\n\nSee the correlation diagram in\nhttp://grb.rssi.ru/GRB221009A/GRB221009_Amati_1st_episode.png\n\nThe softness of the spectrum is also confirmed by our analysis of \nSPI-ACS/INTEGRAL data: assuming high values of Epeak (e.g. Epeak = 975 \nkeV) and using SPI-ACS - GBM cross-calibration method to convert SPI-ACS \ncount fluxes to energy units (Minaev et al., in preparation) we obtain \nunderestimated value of fluence F_ACS = (1.3 +/- 0.3)E-5 erg/cm^2  for \nEpeak = 975 keV, which is less than reference value of F_GBM = (2.38 +/- \n0.04)E-5 erg/cm^2 in (10, 1000) keV range, calculated within our power \nlaw model with gamma = -1.68.\nUsing data of GBM/Fermi we perform cross-correlation analysis of the \ninitial episode and find significant spectral lags, typical for type II \n(long) GRBs (e.g. Minaev et al., Astronomy Letters, 40, 5, 235, 2014). \nSpectral lag ��� energy dependence is fitted satisfactory by logarithmic \nfunction lag ~ A*log(E) with spectral lag index A = 0.11 +/- 0.03.\n\nThe spectral lag and its parameter can be found in \nhttp://grb.rssi.ru/GRB221009A/GRB221009_GBM_lags_1st_episode.png",
  "circularId": 32819,
  "createdOn": 1666479912000,
  "email": "apozanen@iki.rssi.ru",
  "subject": "GRB 221009A: Analysis of the initial episode using data of GBM/Fermi and SPI-ACS/INTEGRAL",
  "submitter": "Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>",
  "eventId": "GRB 221009A"
}