GCN Circular 21177
Subject
GRB 170531B: Redshift from GTC/OSIRIS
Event
Date
2017-06-01T06:34:45Z (8 years ago)
From
Antonio de Ugarte Postigo at IAA-CSIC <deugarte@iaa.es>
A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), L. Izzo (IAA-CSIC),
D.A. Kann (IAA-CSIC), C.C. Thoene (IAA-CSIC), Z. Cano
(IAA-CSIC), J.P.U. Fynbo (DARK/NBI), D. Garcia Alvarez
(GTC, IAC), D. Perez Valladares (GTC), A. Nu��ez (GTC), M. Huertas (GTC)
report on behalf of a larger collaboration:
We observed the afterglow of GRB 170531B (Evans et al. GCN
21171, Lipunov et al. GCN 21173, Pozanenko et al. GCN 21174)
using OSIRIS at the 10.4 m GTC telescope in La Palma (Spain).
Observation consisted in 3x900s exposures using the R1000B
grism, covering the range between 3700 and 7880 AA. The mean
epoch of the combined spectrum is 03:09:29 UT (5.12 hr after the
GRB onset). Additionally, g, r, i, and z-band observations were
obtained. We note that the coordinates of the afterglow are
19:07:32.09, -16:25:05.8 (J2000 +/-0.5���), which places the GRB
approximately 5��� away from those of the source identified by
Lipunov et al. (GCN 21173) and Pozanenko et al. (GCN 21174).
The afterglow can be also detected in the early Swift/UVOT
images. In the acquisition image we measure a magnitude of
r_AB = 21.9 for the afterglow, as compared to PANSTARRS
catalogue field stars.
The afterglow spectrum shows continuum throughout the
wavelength range and several strong absorption features
corresponding to Lyman-alpha, SiII, OI, CII, SiIV, CIV, AlII and AlII
at a common redshift of 2.366, which we identify as the redshift of
the GRB.
[GCN OPS NOTE(01jun17): Per author's request, authors DPV, AN, & MH
were added to the list.]