[vsnet-grb-info 16748] GRB 150716A: P60 Candidate Optical Afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18029
SUBJECT: GRB 150716A: P60 Candidate Optical Afterglow
DATE:    15/07/16 21:02:36 GMT
FROM:    S. Bradley Cenko at NASA/GSFC  <brad.cenko at nasa.gov>

S. B. Cenko (NASA/GSFC) and D. A. Perley (DARK) report on behalf of a larger collaboration:

We have imaged the location of the X-ray afterglow of GRB 150716A (Kocevski et al., GCN 18027) with the automated Palomar 60 inch telescope.  Observations were obtained in the r, i, and z filters beginning at 07:11 UT (~ 4 minutes after the Swift trigger time) and ending at 8:18 UT.  Within the XRT error circle, we detect a large number of sources, one of which shows marginal evidence for fading:

  RA: 18:33:57.13
  Dec: -12:58:46.3

By comparison with the nearby USNO-B1 catalog star 0770-0591035 (I2 magnitude = 17.66), we measure the following magnitudes for this source:

UT          Magnitude
----------------------------------
07:11      21.48 +/- 0.22
08:17      > 22.15 

The source reported by RATIR (Watson et al, GCN 18028) is clearly detected in our images, but a) does not appear to fade, and b) is outside the revised XRT error circle.

We thank Alan Watson and Nat Butler for sharing the RATIR images with us.