GCN Circular 20108
A. Martin-Carrillo (UCD), D. Murphy (UCD), L. Hanlon (UCD), H. J. van Heerden (UFS), B. van Soelen (UFS) and P. J. Meintjes (UFS) We observed the field of GRB 161023A (Mereghetti et al, GCN 20103) using the 40cm UCD Watcher telescope at Boyden Observatory in South Africa. Observations started at 22:39:23 UT, 43.7 seconds after the burst trigger (T0=22:38:40 UT) when the source was just 21.9 degrees above the horizon. A series of 5 second exposures was taken in the SDSS r��� filter using an Andor EMCCD camera for the first 600 seconds, followed by 60 second exposures until the source was below our observation limit at 22:53:33 UT (T0+893 seconds). A bright transient source is clearly detected in all individual frames consistent with the location reported by Gorbovskoy et al. (GCN 20102). The source shows a fast rise up to ~T0+200 seconds where it peaks at m(r���) ~12.8, followed by a slow decay. On our last measurement at T0+893 seconds, the source had faded to m(r���)~14.4. Magnitudes were calibrated using several nearby APASS stars and are shown in the Vega system. No correction for Galactic extinction in the direction of the GRB has been applied.