{
  "bibcode": "2021GCN.30037....1T",
  "body": "N. R. Tanvir (Univ. Leicester), D. Xu (NAOC/CAS), L. Izzo (DARK/NBI), D. \nA. Kann (HETH/IAA-CSIC), D. B. Malesani (DTU space), J.-B. Vielfaure \n(APC), P. Jakobsson (Univ. Iceland), A. de Ugarte Postigo (HETH/IAA-CSIC \nand DARK/NBI), K. E. Heintz (Univ. Iceland and DAWN/NBI), V. D'Elia \n(ASI/SSDC), A. J. Levan (Radboud Univ.), S. D. Vergani (CNRS, Paris \nObs.), S. Campana (INAF/Brera), G. Pugliese (Amsterdam), report on \nbehalf of the Stargate collaboration:\n\nWe observed the field of GRB 210517A (D'Elia et al., GCN 30032; Ursi et \nal., GCN 30036) using the ESO VLT UT3 (Melipal) equipped with the \nX-shooter spectrograph. Our spectra cover the wavelength range \n3000-21000 AA, and consist of 4 exposures by 600 s each. The observation \nmid time was 2021 May 17.387 UT (3.82 hr after the GRB).\n\nIn a 30 s image taken with the acquisition camera on May 17.364 UT, we \ndetect a single object consistent with the UVOT-enhanced XRT position \n(Beardmore et al., GCN 30034), at J2000 coordinates:\n\nRA = 23:52:53.95\nDec = -39:06:08.3\n\nWe measure for this target an AB magnitude r = 22.3 +- 0.1 (calibrated \nagainst the Legacy Survey, but only very few, faint stars are present in \nthe acquisition camera field of view). We note that at the same \nposition, to within the uncertainties, there is a faint object visible \nin the Legacy Survey, with AB magnitude r ~ 23.7. We conclude that the \nabove source is the optical afterglow of GRB 210517A, and the archival \nobject is its host galaxy.\n\nIn our spectra, continuum is detected over the whole observed range. A \nprominent emission line is detected around 4236 AA, which we identify as \nLy alpha in emission. This interpretation is confirmed by the detection \nof both emission lines in the near-infrared arm (corresponding to [O II] \nand [O III]), and a plethora of metallic absorption features, among them \nSi II, Si IV, O I, C IV, C II, all at a common redshift z = 2.486. \nConsistent with the detection of bright Ly alpha in emission, the \nobserved HI absorption column density is low.\n\nWe note that at z = 2.486 the galaxy is a particularly bright GRB host, \nwith an absolute AB magnitude M(1800 AA) ~ -21.5.\n\nWe acknowledge excellent support from the ESO observing staff in \nParanal, in particular Luca Sbordone, Francisco Caceres, and Boris \nHaeussler.",
  "circularId": 30037,
  "createdOn": 1621256820000,
  "email": "malesani@space.dtu.dk",
  "subject": "GRB 210517A: VLT/X-shooter optical afterglow and redshift",
  "submitter": "Daniele B Malesani at DTU Space  <malesani@space.dtu.dk>",
  "eventId": "GRB 210517A"
}