TITLE: GCN CIRCULAR NUMBER: 7680 SUBJECT: GRB 080503: No further optical rebrightening DATE: 08/05/05 13:15:41 GMT FROM: Daniel Perley at U.C. Berkeley D. A. Perley and J. S. Bloom (UC Berkeley) report on behalf of a larger collaboration: Starting at UT 11:32 on the night of 2008-05-05, we began a series of additional r-band imaging follow-up observations of the optical counterpart associated with GRB 080503 (GCN 7665, Mao et al.), using Gemini-North (+GMOS). The new source (s2) reported in our previous circular (GCN 7678) is still present at about the same magnitude. Using a stack of 9x180s images, we present the following measurement of the magnitudes of s1 and s2: s1: R = 26.33 +/- 0.20 s2: R = 25.46 +/- 0.09 This is consistent (within about 2-sigma) with the previous night's measurement and suggests neither additional rebrightening nor dramatic fading. We continue to strongly encourage follow-up with large-aperture instruments. We also issue the following correction to GCN 7678: the data table at the bottom (with heading "UT_start exposure filter magnitude") is not valid. This is photometry of s1 based on an older calibration, and including a Keck R-band limiting magnitude that will be refined in a future circular. The preceding photometry of s1 and s2 in that circular is still valid. To reiterate, the r-band evolution of the optical counterpart (s2) to date, calibrated to USNO B1.0 R-band, is given by: t(hr) magnitude 0.98 R > 25.6 1.5 R > 26.5 26.0 R = 25.28 +/- 0.09 47.4 R = 25.46 +/- 0.09 Further observations are ongoing.