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GCN Circular 25639

Subject
LIGO/Virgo S190901ap: Keck I LRIS spectroscopy of ZTF19abvizsw
Date
2019-09-04T00:27:15Z (5 years ago)
From
Mansi M. Kasliwal at Caltech/Carnegie <mansikasliwal@gmail.com>
Kevin Burdge (Caltech), Daniel A. Perley (LJMU) and Mansi M. Kasliwal
(Caltech) report on behalf of the GROWTH collaboration:

We obtained a Keck I LRIS spectrum of ZTF19abvizsw (Kool et al. GCN
25616).  The reduced spectrum shows a featureless continuum superimposed
with a number of narrow absorption lines, including Mg II, Mg I, and Fe II
at a consistent redshift of z=1.26.

This is far beyond the GW distance constraints on S190901ap (LVC et al. GCN
25614, GCN 25606) and demonstrates that this source is unrelated to the
LIGO/Virgo source.  It could be a flaring AGN or blazar, but there is no
counterpart in PS1 or WISE and only a dim, marginal object at this location
in the Legacy Survey.  It may also be a GRB afterglow.

Our conclusions disagree with those of Salmaso et al. (GCN 25618), who
reported an M- or K-dwarf spectrum for this object.  We note that there is
a bright, red star less than 2 arcsec away from the transient position and
it is possible that the spectrum reported in GCN 25618 may correspond to
that object.
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