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GCN Circular 19350

Subject
GRB 160425A VLT/X-shooter redshift
Date
2016-04-26T09:28:42Z (8 years ago)
From
Nial Tanvir at U.Leicester <nrt3@star.le.ac.uk>
N. R. Tanvir (U. Leicester), D. Xu (NAO/CAS), T. Kruehler (MPE),
D. Malesani, J. P. U. Fynbo (DARK/NBI), G. Pugliese (U. Amsterdam),
A. J. Levan (U. Warwick), Z. Cano (U. Iceland) report on behalf
of a larger collaboration:

We observed the optical counterpart of the unusual
GRB 160425A (Krimm et al., GCN 19343) 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 April 26.26 UT
(approx 6.9 hr after the GRB) and consisted of 4 exposures of
1200 s each.

In our acquisition images, we detect an extended object
consistent with the position of the UVOT counterpart,
whose morphology exhibits two knots separated by ~1.2". 
That object is faintly visible in the digitized sky survey, 
and is likely the host galaxy of GRB 160425A.

The spectrum reveals two distinct systems at z=0.555, based 
on emission lines of Halpha, Hbeta, [O III], [O II] and [S III].  
The velocity separation between them is ~180 km/s, and the 
spatial separation is consistent with the two knots seen in
the imaging (corresponding to ~8 kpc at this distance), 
suggesting an interacting pair of galaxies. 

We acknowledge expert support from the ESO observing staff, 
particularly Jose Velazquez and Juan Carlos Munoz, in obtaining 
these observations.
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