TITLE: GCN CIRCULAR NUMBER: 7488 SUBJECT: GRB 080320: Gemini-N optical afterglow DATE: 08/03/20 17:00:48 GMT FROM: Nial Tanvir at IofA U.Cambridge N. R. Tanvir, E. Rol (U. Leicester), A. Stephens (Gemini), report on behalf of a larger collaboration: We obtained griz observations of the field of GRB 080320 starting approximately 80 mins post-burst with Gemini-N/GMOS. Conditions were rather poor, with some cirrus, which reduced the depth of the images. A 2nd epoch of i-band imaging was obtained 9 hours post-burst. A fading point source is seen in both i-band images, somewhat outside the enhanced XRT error circle (GCN 7479). The position (J2000) of this counterpart, with respect to nearby SDSS stars, is (to 0.25 arcsec in each coordinate): RA = 11 50 56.427 dec= +57 09 23.90 The SDSS galaxy noted in GCN 7480 is about 3 arcsec away from the counterpart, and therefore probably unrelated to it. Preliminary photometry (again relative to SDSS field stars) gives i'=22.9, and fading between the epochs of 0.37+/-0.03 mag. This relatively slow rate of fading could indicate a contribution from a host galaxy. The counterpart is seen in the z-band, but is absent (or very faint) in the r-band image with a limit of about r~24. This red r-i colour could be explained by a Lyman-alpha break if the redshift is z~4.5 to 5. Further analysis is ongoing.