[vsnet-grb-info 15612] GRB 141005A: Additional P60 imaging and afterglow confirmation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16901
SUBJECT: GRB 141005A: Additional P60 imaging and afterglow confirmation
DATE:    14/10/07 06:04:59 GMT
FROM:    Daniel Perley at Caltech  <dperley at astro.caltech.edu>

S. B. Cenko (NASA/GSFC) and D. A. Perley (Caltech) report:

We obtained a second epoch of imaging at the location of the optical 
afterglow (Perley et al., GCN 16884; Littlejohns et al., GCN 16885; 
Schmidl et al., GCN 16898) of GRB 141005A (D'Elia et al., GCN 16882) 
with the robotic Palomar 60 inch telescope.  Observations were obtained 
in the r', i', and z' filters beginning at 2:31 UT on 2014 October 6 
(0.89 d after the burst).

A source is clearly detected at the location of the afterglow candidate 
originally reported in GCN 16884 (Perley et al).  As noted therein, a 
source is also present at this location in pre-outburst SDSS imaging of 
this field.

To search for variability at this location, we performed digital image 
subtraction with the P60 data, using the images from 2014 October 6 as a 
reference template.  We find clear evidence for fading in the i-band 
(and marginal evidence in r and z-bands), confirming that this source is 
indeed the optical afterglow of GRB 141005A but is blended with a bright 
(i' ~ 21.7 mag) host galaxy or foreground object.   Assuming no 
contribution of the afterglow to our template images, we measure i' = 
20.24 +/- 0.10 at 5:18 UT on 2014 October 5 (i.e., 5 min after the Swift 
trigger).