TITLE:   GCN CIRCULAR
NUMBER:  17312
SUBJECT: GRB 150120A: P60 optical observations
DATE:    15/01/20 04:06:55 GMT
FROM:    Daniel Perley at Caltech  <dperley@astro.caltech.edu>

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

The Palomar 60-inch robotic telescope began automatic follow-up of the 
location of possibly-short GRB 150120A (D'Elia et al. GCN 17310) 
starting at 2015-01-20 03:00:33 UT, approximately 2.7 minutes after the 
GRB trigger.  A sequence of rotating r, i, and z 60-second exposures was 
acquired, followed by five 180-second exposures in each of r and i 
bands, under good conditions.

No sources are clearly detected inside the enhanced XRT error circle 
(Evans et al., GCN 17311), either in either individual exposures or in 
stacks of all 60-second exposures taken in each filter (approximate UT 
center time 15 minutes post-trigger, limiting magnitudes r>22.5, i>22.4, 
z>20.9).  We detect two faint sources slightly outside the error circle 
in the stacked frames:

  Source A:  RA=00:41:16.55, dec=+33:59:42.87
  Source B:  RA=00:41:16.76, dec=+33:59:42.11

Both sources appear to be marginally detected in SDSS pre-imaging and we 
do not yet have evidence of fading behavior.  Further observations and 
analysis are ongoing.

[GCN OPS NOTE(20jan15):  Per author's request, the date in the third line
was changed from 2015-01-t0 to 2015-01-20.]