GCN Circular 19971
Subject
GRB 161001A: X-shooter spectroscopy, candidate host galaxy and redshift
Date
2016-10-01T12:57:15Z (8 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@dark-cosmology.dk>
T. Kruehler (MPE Garching), D. Xu (NAOC/CAS), J. Bolmer (MPE Garching
and ESO Santiago), K. Wiersema (Univ. Leicester), D. Malesani (DARK/NBI
and DTU Space), R. Sanchez-Ramirez (IAA-CSIC), J. P. U. Fynbo
(DARK/NBI), report on behalf of a larger collaboration:
We observed the field of GRB 1601001A (Page et al., GCN 19967) with the
ESO Very Large Telescope Unit 2 (Kueyen) equipped with the X-shooter
spectrograph.
Close to, but outside, the enhanced XRT position (Osborne et al., GCN
19969), in our acquisition image we detect a bright, pointlike source at
coordinates RA = 04:47:40.71, Dec = -57:15:36.8. This source is faintly
visible in the archival DSS data and is pointlike in our images (0.75"
seeing).
A spectrum was secured of this object, for a total of 4x600 s, starting
on Oct 1.299 UT (6.1 hr after the GRB). The continuum is consistent with
a stellar spectrum, and we conclude that this target is not associated
with GRB 161001A.
Our slit, at a position angle of 319.6 deg (CCW from north), does
however cover a portion of the XRT error circle. Within the wings of the
the PSF of the DSS object, approximately 0.8 arcsec SE, we detect a
number of emission lines which are consistent with [O II], Hbeta, [O
III] and Halpha at a common redshift of z = 0.891, revealing the
presence of a background object. While we cannot accurately determine
its position from the slit information alone, that is consistent with
being at the edge of the XRT error circle. Our images also hint a faint
extension of the DSS object at a position consistent with that of the
emission lines, which could represent the continuum emission of the
object. As such, this is a candidate host galaxy of GRB 161001A.
We caution that we have no way to confirm the association between the
emission line object and the GRB. No variability can be inferred from
our data, and as we lack an estimate of the continuum flux, we can not
presently quantify the chance association probability.
A finding chart showing the region surrounding the XRT position is shown
at this URL:
http://www.astro.ku.dk/~malesani/GRB/161001A/GRB161001A_slit.png
We acknowledge excellent support from the ESO observing staff at
Paranal, in particular Zahed Wahhaj, Jonathan Smoker, and Claudia Cid.
