{
  "bibcode": "2020GCN.28764....1D",
  "body": "A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D. A. Kann, M. Blazek, \nJ. F. Agui Fernandez, C. C. Thoene (all HETH/IAA-CSIC), S. Geier, and M. \nRivero (both GRANTECAN) report:\n\nWe observed the afterglow (Lipunov et al., GCN#28760, Marshall et al., \nGCN#28761, Fernandez-Garcia et al., GCN#28763) of GRB 201024A (Marshall \net al., GCN#28761) with the 10.4m GTC telescope, at Roque de los \nMuchachos Observatory (La Palma, Spain) equipped with OSIRIS. The \nobservation started on 24 October 2020 at 03:28:47 UT (0.663 hrs after \nthe GRB onset) and consisted of 3 x 900 s with the R1000B grism, \ncovering the wavelength range between 3700 and 7800 AA. Observations \nwere taken under good conditions but high airmass.\n\nAt the afterglow position, a clear source is detected. We measure r' ~ \n19.3 mag (AB) vs. nearby PanSTARRS field stars. This indicates the \nsource has faded rapidly vs. the early MASTER/BOOTES detection, as \nLipunov et al., GCN#28760 and Fernandez-Garcia et al., GCN#28763 stated.\n\nA preliminary reduction of the spectrum shows a clear continuum, with \nMnII, FeII, FeII*, MgII, and MgI absorption lines, as well as the [OII] \ndoublet in emission, all at a common redshift of z = 0.999, which we \nidentify as the redshift of the GRB.\n\nWe furthermore note that there is an underlying galaxy at the OT \nposition visible in SDSS and PanSTARRS, at r ~ 21.15 mag. We also see a \nsecond galaxy offset by a few arcsec in our finding chart.\n\nWe thank P. D'Avanzo and L. Izzo for pointing out the galaxy.",
  "circularId": 28764,
  "createdOn": 1603513735000,
  "email": "kann@iaa.es",
  "subject": "GRB 201024A: Redshift from GTC/OSIRIS",
  "submitter": "Alexander Kann at IAA-CSIC  <kann@iaa.es>",
  "eventId": "GRB 201024A"
}