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GCN Circular 21197

Subject
GRB 170604A: GTC spectroscopic redshift
Date
2017-06-05T08:04:01Z (7 years ago)
From
Zach Cano at U of Iceland <zewcano@gmail.com>
L. Izzo, Z. Cano (IAA-CSIC), A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), D.
A. Kann (IAA-CSIC), C. C. Thoene (IAA-CSIC), A. Marante (GTC) and S. Geier
(GTC, IAC) report on behalf of a larger collaboration:

We observed the afterglow of GRB 170604A (Page et al., GCN Circ. 21191)
using OSIRIS at the 10.4 m GTC telescope at La Palma (Spain). The
observation consisted of 2x900s and 1x1200s exposures using the R1000B
grism, which covers a wavelength range of 3700-7880 AA.  Observations began
at 04:14:19 UT on the morning of 05 June, 2017, at a mean epoch of +9.51
hrs from the GRB detection.  The afterglow candidate (Izzo et al, GCN Circ.
21192) is detected in the r-band acquisition image, where we measure r =
20.3 +- 0.1 relative to nearby PANSTARRS standards in the GRB field of
view.

The afterglow spectrum shows a continuum through the observed wavelength
range, and we identify absorption features corresponding to MgII, MgI, and
FeII at a common redshift of z=1.329, which we identify as the redshift of
GRB 170604A.
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