TITLE: GCN CIRCULAR NUMBER: 6387 SUBJECT: GRB 070508: Optical observation limiting magnitude DATE: 07/05/08 09:56:54 GMT FROM: Alan Gilmore at U of Canterbury,Mt John Obs A. C. Gilmore and P. M. Kilmartin (Mt John Observatory of the University of Canterbury) report: We stacked 20 x 120 second clear exposures of the GRB 070508 taken with a SBIG ST9e CCD on a 0.6 m f/6.4 reflector at Mt John Observatory. The exposure set was centred on May 8 07:49 UT (3.5 hours after the burst). Our images do not show any object at the coordinates given by Berger (GCN 6386) to a limiting R magnitude of approximately 20.5 based on USNO B1.0 stars. These observations were made as part of the AAVSO GRB Network, and supported by a grant from the Curry Foundation.