{
  "bibcode": "2022GCN.32686....1C",
  "body": "A. J. Castro-Tirado, R. Sanchez-Ramirez, Y.-D. Hu, M.D. \nCaballero-Garcia, M. A. Castro Tirado, E. Fernandez-Garcia, I. \nPerez-Garcia (IAA-CSIC), G. Lombardi (GTC, IAC), S. B. Pandey (ARIES), \nJ. Yang (NJU) and B.-B. Zhang (NJU) on behalf of a larger collaboration, \nreport:\n\nFollowing the detection of the extraordinarily bright GRB 221009A \ndetected by Swift, Fermi, MAXI/GSC, INTEGRAL (SPI-ACS), Konus-Wind, the \nIPN, AGILE/MCAL, SolO/STIX, SRG/ART-XC, CALET and GRBAlpha (Dichiara et \nal. GCNC 32632, Veres et al. GCNC 32636, Bissaldi et al. GCNC 32637, \nSvinkin et al. GCNC 32641, Negoro et al. ATEL 15651, Ursi et al. GCNC \n32650, Xiao et al GCNC 32661, Lapshov et al. GCNC 32663, Cannady et al. \nGCNC 32674, Ripa et al. GCNC 32685), we triggered the 10.4m Gran \nTelescopio de Canarias (GTC) equipped with Optical System for Imaging \nand low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) in La \nPalma (Spain), starting on Oct 9, 22:19 UT (~9 hrs after the GBM \ntrigger). Spectroscopy was obtained with both the R1000B (2x900s) and \nR1000R (2x300s) grisms, covering the 363-1000 nm spectral range. A red \ncontinuum is noticeable, in agreement with earlier reports by Perley \n(GCNC 32638) and Xu et al. (GCNC 32647). The GTC spectrum clearly shows \nthe Ca II H & K absorption doublet implying a redshift of z=0.1505, \nconsistent the value derived from X-shooter/VLT (de Ugarte Postigo et \nal. GCNC 32648). ��With this redshift of z= 0.1505, a time-averaged peak \nenergy of 2.52 MeV and a total fluence of 2.6e-2 erg cm^-2, ��we found \nthat the main emission episode (between 174 and 700 s post trigger) of \nGRB 221009A is consistent with the Type II (collapsar origin; Zhang et \nal, 2007, 2009) bursts in the Ep-Eiso diagram (Amati et al. 2002).\n\nWe thank the staff at GTC for their excellent support.",
  "circularId": 32686,
  "createdOn": 1665495464000,
  "email": "ajct@iaa.es",
  "subject": "GRB 221009A: 10.4m GTC spectroscopic redshift confirmation",
  "submitter": "Alberto J. Castro-Tirado at IAA-CSIC  <ajct@iaa.es>",
  "eventId": "GRB 221009A"
}