{
  "bibcode": "2021GCN.30771....1T",
  "body": "N. Tanvir (Univ. Leicester), A. Rossi (INAF-OAS), D. Xu (NAOC), Z.P. Zhu \n(NAOC,HUST), L. Izzo (DARK/NBI), D. A. Kann (HETH/IAA-CSIC), and A.J. \nLevan (Radboud) report on behalf of the Stargate collaboration:\n\nWe observed the location of the afterglow (Strausbaugh & Cucchiara, GCN \n30769, 30770) of GRB 210905A (Sonbas et al., GCN 30765) using the ESO \nVLT UT3 (Melipal) equipped with the X-shooter spectrograph. Our spectra \ncover the wavelength range 3000-21000 AA, and consist of 4 exposures by \n1200 s each. Our observations started on 2021 September 05 at 02:44 UT, \n~2.53 hours after the GRB detection.\n\nIn the acquisition image obtained between 2.53 and 2.73 hours after the \nburst, the afterglow is well detected at I and z-bands, but not in the \nr-band, confirming the red color already noted by Strausbaugh & \nCucchiara. We measure the following AB magnitudes:\n\nr>23.5\nI=20.3+-0.1\nz=19.4+-0.1\n\nSpectroscopy of the source reveals a continuum well detected in the red \npart of visible arm. A clear break is detected around 9000AA which we \ninterpret as the Lyman-alpha break at z = 6.318, and explains the strong \nr-z color as due to Lyman dropout. Other lines such as Fe II, Al II, C \nIV and Si II are visible and display a double absorption profile, which \nis possibly due to different intervening systems at z1 = 6.312 and z2 = \n6.318. We thus conclude that z=6.318 is the redshift of GRB 210905A. \nFurther analysis is undergoing.\n\nWe acknowledge support from the ESO observing staff at Paranal, in \nparticular Israel Blanchard, Michael Abdul-Masih, and Matias Jones.",
  "circularId": 30771,
  "createdOn": 1630821986000,
  "email": "andrea.rossi@inaf.it",
  "subject": "GRB 210905A: VLT/X-shooter spectroscopic redshift",
  "submitter": "Andrea Rossi at INAF  <andrea.rossi@inaf.it>",
  "eventId": "GRB 210905A"
}