[vsnet-grb-info 14885] GRB 140428A: Keck detection of a red optical afterglow candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16180
SUBJECT: GRB 140428A: Keck detection of a red optical afterglow candidate
DATE:    14/04/29 07:23:15 GMT
FROM:    Daniel Perley at Caltech  <dperley at astro.caltech.edu>

D. A. Perley (Caltech) reports:

I observed the position of GRB 140428A (Kocevski et al., GCN 16177; Page 
et al., GCN 16178) using LRIS on the Keck I 10-meter telescope.  A 
single 150-second imaging exposure was acquired simultaneously in both g 
and i filters.  An faint source is well-detected inside the XRT error 
circle in the i-band image at the following location (J2000):

RA  =  12:57:28.392
dec = +28:23:06.28

However, the object is completely absent in g-band.  Photometry relative 
to SDSS gives magnitudes of:

g > 26.42
i = 23.55 +/- 0.07

at a time of 06:09:30 UT (2014-04-29), 7.478 hours after the GRB trigger.

If this corresponds to the afterglow of the GRB, the red color suggests 
either a (moderately) high-redshift or dust-extinguished event.  Further 
observations are planned.