TITLE:   GCN CIRCULAR
NUMBER:  28661
SUBJECT: GRB 201015A: redshift confirmation
DATE:    20/10/16 18:15:26 GMT
FROM:    Daniele B Malesani at DTU Space  <malesani@space.dtu.dk>

L. Izzo (DARK/NBI), D. B. Malesani (DTU Space), Z.P. Zhu (NAO/CAS, 
HUST), D. Xu (NAO/CAS), A. de Ugarte Postigo (HETH, IAA-CSIC), T. 
Pursimo, report on behalf of a larger collaboration:

We observed the optical counterpart of GRB 201015A (D'Elia et al., GCN 
28632; Lipunov et al., GCN 28634) with the Nordic Optical Telescope, 
equipped with the ALFOSC spectrograph. Spectroscopic observations 
started on 2020 Oct 15.978 UT (38 min after the GRB trigger) and 
consisted of four 900-s exposures with grism #4, covering the wavelength 
range 3800-9400 AA.

A trace is visible across the full spectral range. In the blue part, 
weak absorption features are detected which can be interpreted as Mg II, 
Mg I and Ca II at z = 0.423. Faint emission lines are also detected at a 
consistent redshift, identified as [O II] and Halpha. Our data allow 
thus to confirm the redshift value reported by de Ugarte Postigo et al. 
(GCN 28649) using the GTC. We note that the detection of absorption 
features sets a firm lower limit to the GRB redshift, excluding a chance 
superposition with a background galaxy.

This work made use of the GRBspec database grbspec.iaa.es.