TITLE:   GCN CIRCULAR
NUMBER:  17335
SUBJECT: GRB 150120B: Additional P60 observations
DATE:    15/01/21 03:32:27 GMT
FROM:    Daniel Perley at Caltech  <dperley@astro.caltech.edu>

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

We obtained further observations at the position of the optical 
afterglow (Perley, GCN 17315) of GRB 150120B (D'Elia et al., GCN 17314) 
with the Palomar 60-inch robotic telescope on the night of 2015-01-21 
UT.   In a combined stack of five 300-second r-band exposures we no 
longer detect any significant emission at the location of the optical 
afterglow.  We estimate a limiting magnitude of r>22.7 mag (3 sigma) at 
a mid-time of 02:32:27 UT, t=0.799 days after the GRB.  Relative to our 
previous observations, this suggests a decay power-law slope of at least 
alpha>0.75.