TITLE: GCN CIRCULAR NUMBER: 6771 SUBJECT: GRB 070810b: Image Subtraction of Multiple Keck Observations DATE: 07/09/01 04:05:55 GMT FROM: Daniel Kocevski at UC Berkeley D. Kocevski, J.S. Bloom, C. C. Thoene, and J. Prochaska report: We performed image subtraction between multiple R-band observations of the error box of short burst GRB070810b (Marshall et al., GCN 6743) with the Keck I telescope (+LRIS). The first epoch of observations began at (UT) 2007-08-11 14:45:00 followed by a second epoch six nights later at (UT) 2007-08-17 12:02:00, with equivalent exposures of 630 and 900 seconds respectively. Image subtraction using the public POIS-IPP package(*) software shows no variable sources associated with the S1, S2 XRT positions (GCN 6754 , Starling et al.) or the S3 position (Thoene et al., GCN 6756) nor any significant residual sources within the BAT error circle down to a limiting magnitude of ~25.5 mag in R band. The potential candidate afterglow close to S2, reported by Pozanenko et al. can be resolved as two objects in our images, which show no sign of variability between the two epochs. * See http://pan-starrs.ifa.hawaii.edu/project/IPP/software/