TITLE:   GCN CIRCULAR
NUMBER:  16181
SUBJECT: GRB 140428A: Keck redshift estimate
DATE:    14/04/29 08:49:50 GMT
FROM:    Daniel Perley at Caltech  <dperley@astro.caltech.edu>

D. A. Perley (Caltech) reports:

I re-observed the afterglow candidate of GRB 140428A in longslit mode 
using LRIS on the Keck I 10m telescope.  One 940-second exposure was 
taken using the 400/8500 grating (red camera) and 600/4000 grism (blue 
camera).

In a provisional reduction, the spectrum of the object shows a weak, 
flat continuum between 7000 Angstroms and the red limit of the 
wavelength range at approximately 10100 Angstroms.  The flux sharply 
drops to zero at 7000 angstroms, though there is faint flux detected in 
some places slightly further to the blue.  No trace is detected on the 
blue camera.

If the drop at 7000 Angstroms is interpreted as a DLA and the onset of 
the Lyman-alpha forest, this would indicate a redshift for this object 
of approximately z=4.7.