{
  "bibcode": "2016GCN.19600....1X",
  "body": "D. Xu (NAOC/CAS), D. Malesani (DARK/NBI), J. P. U. Fynbo (DARK/NBI), N. \nR. Tanvir (Univ. Leicester), A. J. Levan (Univ. Warwick), D. A. Perley \n(DARK/NBI), report on behalf of a larger collaboration:\n\nWe observed the optical afterglow of the Fermi GRB 160625B (Dirirsa et \nal., GCN 19580; Burns, GCN 19581; Troja et al., GCN 19588) with the ESO \nVLT UT2 (Kueyen) equipped with the X-shooter spectrograph. Observations \nstarted on 2016 June 27.19 UT (1.25 days after the Fermi trigger) and \nconsisted of 4 spectra by 600 s each, covering the wavelength range \n3500-20000 AA.\n\nThe afterglow is well detected in the acquisition image with R ~ 19.1 +- \n0.3, where the large error is due to scatter in the USNO magnitudes used \nas reference, and the r versus R filter transformation.\n\nThe continuum trace is well detected in our exposures, down to ~3100 AA. \nThe lack of any drop sets an upper limit to the redshift z < 1.55. A \nnumber of superimposed absorption features are visible; among others, we \ndetect Mg I, Mg II, Fe II, C IV, Si IV, O I, Si II, Zn II, Al II, and Al \nIII, all at a common redshift z = 1.406, which we conclude to be the \nredshift of GRB 160625B. We also detect an intervening Mg II absorption \nsystem at z = 1.319.\n\nAt z = 1.406, the fluence in the 10-1000 keV Fermi band (Burns, GCN \n19587) corresponds to an isotropic-equivalent energy of ~2.5*10^54 erg.\n\nWe acknowledge excellent support from the ESO observing staff in \nParanal, in particular Juan Carlos Munoz, Elizabeth (Liz) Bartlett, \nDimitri Gadotti and Francisco Caceres.",
  "circularId": 19600,
  "createdOn": 1467021038000,
  "email": "malesani@dark-cosmology.dk",
  "subject": "GRB 160625B: VLT/X-shooter redshift",
  "submitter": "Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani@dark-cosmology.dk>",
  "eventId": "GRB 160625B"
}