[vsnet-grb-info 18656] GRB 161023A VLT/X-shooter redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20104
SUBJECT: GRB 161023A VLT/X-shooter redshift
DATE:    16/10/24 03:17:06 GMT
FROM:    Nial Tanvir at U.Leicester  <nrt3 at star.le.ac.uk>

N. R. Tanvir (U. Leicester), T. Kruehler (MPE), A. De Cia (ESO),
K. Wiersema (U. Leicester), D. Xu (NAOC), D. Malesani (DARK/NBI),
report on behalf of a larger collaboration:

We observed the optical counterpart of the bright INTEGRAL
GRB 161023A (Mereghetti et al. GCN 20103; Gorbovskoy et al.
GCN 20102) with the ESO Very Large Telescope UT 2 (Kueyen)
equipped with the X-shooter spectrograph, covering the wavelength
range 3500-20000 AA.  Observations started on October 24.05 UT
(approx 3.0 hr after the GRB) and consisted of 2 exposures of
600 s each.

The spectrum exhibits numerous absorption features including the
hydrogen Lyman series, and lines of SII, SiII, SiIV, CIV, AlII, FeII, OI,
several of which are fine structure lines, at a redshift of z=2.708. We
conclude this is the redshift of the GRB.

We acknowledge the generosity of the visiting observer, Chris D'Andrea,
who approved the override, and expert support from the ESO observing
staff, particularly Linda Schmidtobreick, in obtaining these observations.