[vsnet-grb-info 16303] GRB 150314A: P60 observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17584
SUBJECT: GRB 150314A: P60 observations
DATE:    15/03/15 01:06:49 GMT
FROM:    Daniel Perley at Caltech  <dperley at 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 GRB 150314A (Hagen et al., GCN 17573) at 05:08:40 UT on 
2015-03-14, 13.4 minutes after the GRB trigger.   A sequence of 
60-second r, i, and z exposures were acquired, lasting until 06:36 UT. 
Another sequence of 180-second g, r, and i exposures was taken between 
09:01 UT and 10:54 UT.

We detect the optical afterglow reported by Zheng and Filippenko (GCN 
17574) in individual exposures from the early sequence as well as in a 
stack of the later-time exposures.  Calibrating to a nearby USNO star 
(RA=126.701423, dec=63.829609,  R2=15.33) gives the following photometry:

t_med = 834s   : R = 18.59 +/- 0.05
t_med = 1179s  : R = 18.96 +/- 0.05
t_med = 1437s  : R = 19.06 +/- 0.07
t_med = 1693s  : R = 19.41 +/- 0.07
t_med = 1977s  : R = 19.59 +/- 0.08
t_med = 18365s : R = 21.73 +/- 0.13

The afterglow fades as approximately t^-0.9 throughout our observations.