{
  "bibcode": "2020GCN.28840....1V",
  "body": "J.-B. Vielfaure (GEPI, Paris Observatory), D. B. Malesani (DTU Space), \nD. A. Kann (HETH/IAA-CSIC), B. Sbarufatti (PSU), N. R. Tanvir (Univ. \nLeicester), and D. H. Hartmann (Clemson University) report on behalf of \nthe Stargate Consortium:\n\nWe observed the optical afterglow (Marshall et al., GCN 28827) of GRB \n201104B (Sbarufatti et al., GCN 28825) using the ESO VLT UT3 (Melipal) \nequipped with the X-shooter spectrograph. Our spectra cover the \nwavelength range 3000-21000 AA, and consist of 2 exposures of 1200 s \neach. The observation mid-time was 2020 Nov 5.0831 UT (8.431 hr after \nthe GRB).\n\nIn a 60 s image taken with the acquisition camera on Nov 5.0596 UT, we \ndetect the optical afterglow, for which we measure a magnitude r = 21.01 \n+/- 0.02 mag (AB magnitude, calibrated against nearby stars from the \nPan-STARRS catalog; Chambers et al. 2016, arXiv:1612.05560).\n\nWe clearly detect continuum over the entire wavelength range. A trough \nis visible around 3590 AA, which we identify as due to H I. From \ndetection of multiple absorption features, which we interpret as due to \nSiII, CI, CII, SiIV, CIV, FeII, AlII, AlIII, MgII, we infer a redshift z \n= 1.954. In particular, fine structure lines from Fe II* are visible, \nwhich confirm the association of the absorption system with the GRB. \nEmission lines are also detected, which we interpret as due to [O II], \nHbeta, [O III], and Halpha at the same redshift.\n\nWe acknowledge excellent support from the ESO observing staff in \nParanal, in particular Florian Rodler, Ivan Aranda, and Matias Jones.\n\n[GCN OPS NOTE(06nov2020): Per author's request, has two changes:\n1) from \"which we interpret as due to [O II], [O III], ad Halpha\"\nto \"which we interpret as due to [O II], Hbeta, [O III], and Halpha\"\n2) adding Ivan Aranda, and Matias Jones to the acknowledgement list.]",
  "circularId": 28840,
  "createdOn": 1604545380000,
  "email": "kann@iaa.es",
  "subject": "GRB 201104B: VLT/X-shooter redshift",
  "submitter": "Alexander Kann at IAA-CSIC  <kann@iaa.es>",
  "eventId": "GRB 201104B"
}