TITLE:   GCN CIRCULAR
NUMBER:  16567
SUBJECT: GRB 140710A: P60 Confirmation of Afterglow
DATE:    14/07/10 14:35:19 GMT
FROM:    S. Bradley Cenko at NASA/GSFC  <brad.cenko@nasa.gov>

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

We observed the location of GRB140710A (Siegel et al., GCN 16563) with the robotic Palomar 60 inch telescope.  Observations were obtained in the r', i', and z' filters beginning 3.1 minutes after the Swift trigger time.  We detect a faint source within the XRT error circle in all three filters, roughly consistent with the location of the candidate reported by GROND (Tanga et al., GCNs 16565; Delvaux, GCN 16566).  Using several nearby point sources from the APASS catalog for calibration, we measure the following AB magnitudes:

r' = 19.90 at dt = 3.6 min 
i' = 19.80 at dt = 5.0 min

Over the course of the first hour following the Swift trigger time, the source fades by >~ 1.0 mag in r', confirming that it is indeed the optical afterglow of GRB140710A.