[vsnet-grb-info 19362] GRB 170428A: GTC spectroscopic redshift of candidate host galaxy

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21059
SUBJECT: GRB 170428A: GTC spectroscopic redshift of candidate host galaxy
DATE:    17/05/02 17:43:47 GMT
FROM:    Zach Cano at U of Iceland  <zewcano at gmail.com>

​​L. Izzo, Z. Cano (IAA-CSIC), A. de Ugarte Postigo (IAA-CSIC, DARK/NBI),
D. A. Kann, C. Thoene (IAA-CSIC), and S. Geier (IAC, GRANTECAN) report on
behalf of a larger collaboration:

We observed the field of short-duration GRB 170428A (Beardmore et al., GCN
Circ. 21042) with OSIRIS mounted on the 10.4-m GTC telescope on La Palma
(Spain) starting at 04:31:49 UT on 01 May 2017, at a mean time of +2.82
days from the GRB detection. The observations consisted of 4 x 900 s
spectra using grism R1000R, which covers the wavelength range between 5100
and 10000 AA.

In our r-band acquisition image, (30 second exposure time), we see the host
candidate of Xu et al. (GCN Circ. 21048), which is also slightly visible in
the r-band Pan-STARRS image.  The slit was centred on the host galaxy
candidate, and in the faint trace we detect emission lines corresponding to
Halpha, [OIII] 5007, Hbeta, and [OII] 3726,3729, all at a common redshift
of z=0.454.  The angular separation between the candidate host and the GRB
position determed by GROND (Bolmer et al., GCN Circ. 21050) is 1.2'' +-
0.3'', which at this redshift implies an offset of 6.9 kpc +- 1.7 kpc.

GTC finder chart of the AG position and candidate host:
http://www.iaa.es/~deugarte/GRBs/170428A/GTC.jpeg