TITLE:   GCN CIRCULAR
NUMBER:  17744
SUBJECT: GRB 150423A: Keck redshift of neighboring galaxy
DATE:    15/04/24 09:15:25 GMT
FROM:    Daniel Perley at Caltech  <dperley@astro.caltech.edu>

D. A. Perley (Caltech) reports:

Further to GCN 17733, I report analysis of the spectroscopy acquired of 
  S2, the neighboring object located 4.0 arcseconds northeast of the 
optical afterglow of GRB 150423A, first announced by Varela et al. (GCN 
17732).

The spectrum of this object shows weak emission lines from OII (3727), 
OIII (5007), Halpha (6563), and marginally Hbeta (4861), all at a common 
redshift of z=0.456.  No features are visible in the trace of S1 at any 
of the same wavelengths (or elsewhere in its spectrum).

At this redshift, the offset between the sources corresponds to 23 kpc 
in projection.

Further observations of S1 will be necessary to determine whether it is 
entirely afterglow or if it also contains flux from a (coincident) host 
galaxy, perhaps at a different redshift.