{
  "bibcode": "2020GCN.28765....1K",
  "body": "D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, \nDARK/NBI), M. Blazek, J. F. Agui Fernandez, C. C. Thoene (all \nHETH/IAA-CSIC), S. Geier, and M. Rivero (both GRANTECAN) report:\n\nWe observed the afterglow (Lipunov et al., GCN#28718; Xu et al., \nGCN#28719; Belkin et al., GCN#28725; Breeveld & Lien, GCN#28743; Vinko \net al., GCN#28750; Kumar et al., GCN#28753) of GRB 201020B (Fermi GBM \nTeam, GCN#28702; Fermi GBM detection: Malacaria & Meegan, GCN#28710; \nFermi LAT detection: Arimoto et al., GCN#28716; AGILE detection: Ursi et \nal., GCN#28714; Konus-Wind detection: Ridnaia et al., GCN#28723) with \nthe 10.4m GTC telescope, at Roque de los Muchachos Observatory (La \nPalma, Spain) equipped with OSIRIS. The observation started on 24 \nOctober 2020 at 04:05:16 UT (3.438 days after the GRB trigger, following \na period of inclement weather) and consisted of 4 x 1200 s with the \nR1000B grism, covering the wavelength range between 3700 and 7800 AA. \nObservations were taken under good conditions.\n\nAt the afterglow position, a source is clearly detected. We measure i' ~ \n21.45 mag (AB) vs. a nearby PanSTARRS field star. This represents a \nsignificant decay compared to the value reported by Vinko et al. \n(GCN#28750). The afterglow is seen to decay with a slope of 1.68, in \nfull agreement with Kumar et al. (GCN#28753).\n\nA preliminary reduction of the spectrum shows a clear but featureless \ncontinuum. There is an emission feature, which we identify as due to the \n[OII]3727 doublet at z = 0.804. Other interpretations (as Hbeta, [OIII] \nor Halpha) would imply other emission lines should be visible, which \nthey are not. At the same redshift there could be marginal, weak \nfeatures consistent with FeII, MgII, and MgI. Therefore, we suggest z = \n0.804 as the redshift of the GRB.",
  "circularId": 28765,
  "createdOn": 1603520971000,
  "email": "kann@iaa.es",
  "subject": "GRB 201020B: Redshift from GTC/OSIRIS",
  "submitter": "Alexander Kann at IAA-CSIC  <kann@iaa.es>",
  "eventId": "GRB 201020B"
}