{
  "bibcode": "2021GCN.29944....1X",
  "body": "D. Xu (NAOC), P. Schady (Univ. Bath), K. E. Heintz (Univ. Iceland and \nDAWN/NBI), D. B. Malesani (DTU Space), B. Sbarufatti (PSU), G. Pugliese \n(API, Univ. Amsterdam), D. A. Perley (LJMU), V. D'Elia (ASI/SSDC, \nINAF/OAR), D. A. Kann (HETH/IAA-CSIC), and J. P. U. Fynbo (DAWN/NBI/DTU) \nreport on behalf of the Stargate consortium:\n\nWe observed the optical afterglow (Breeveld & Beardmore, GCN 29933; \nHeintz et al., GCN 29937) of GRB 210504A (Beardmore et al., GCN 29929; \nLien et al., GCN 29330) using the ESO VLT UT3 (Melipal) equipped with \nthe X-shooter spectrograph. Our spectra cover the wavelength range \n3000-21000 AA, and consist of 4 exposures of 1200 s each (8 x 600 s in \nthe NIR). The observation mid-time was 2021 May 05.06 UT (11.6 hr after \nthe GRB).\n\nIn a 60 s image taken with the acquisition camera on May 05.02 UT, we \ndetect the optical afterglow, for which we measure an AB magnitude r' = \n21.11 +- 0.04 mag (calibrated against nearby stars from the Pan-STARRS \ncatalog).\n\nWe clearly detect continuum over the wavelength range of the entire \nspectrum. A trough is visible around 3740 AA, which we identify as due \nto H I. From the detection of several absorption features, which we \ninterpret as due to Si II, C II, C IV, Fe II, Al II, Mg II, among \nothers, as well as the Lyman forest, we infer a redshift z = 2.077.\n\nWe acknowledge excellent support from the observing staff at Paranal, in \nparticular Steffen Mieske, Ditte Slumstrup and Diego Parraguez.",
  "circularId": 29944,
  "createdOn": 1620200180000,
  "email": "kann@iaa.es",
  "subject": "GRB 210504A: VLT X-shooter redshift",
  "submitter": "Alexander Kann at IAA-CSIC  <kann@iaa.es>",
  "eventId": "GRB 210504A"
}