TITLE: GCN CIRCULAR NUMBER: 8106 SUBJECT: GRB080810 - optical observations DATE: 08/08/16 21:42:53 GMT FROM: Christina Thoene at Niels Bohr Institute,DARK Cosmo Ctr Christina C. Thoene (DARK/NBI), Antonio de Ugarte Postigo (ESO) and Christine Liebig (ARI Heidelberg) report: We observed the field of GRB 080810 (Page et al. GCN 8080) with the Danish 1.54m telescope on La Silla/Chile on August 15.40 UT and 16.31 UT (4.85 and 5.76 days after the burst onset). We detect the decaying afterglow at preliminary R-band magnitudes of 22.8+/-0.3 and 23.2+/-0.5. Using the R band and unfiltered magnitudes published in GCNs (Rykoff et al. GCN 8084, Burenin et al. GCN 8088, de Ugarte Postigo et al. GCN 8089 & 8090, Okuma et al. GCN 8091, Kocka et al. GCN 8092, Guidorzi et al. GCN 8093 & 8099, Andreev et al. GCN 8094, Yoshida et al. GCN 8097, Galeev et al. GCN 8098 & 8102, Rumyantsev et al. GCN 8105) together with the data of our own observations we find that the light curve can be described by a powerlaw of index alpha = 1.12 +/- 0.02 between 400s and 1 day after the burst. After 1 day there is a flux excess that can be seen both in the optical and X-ray light curves (explaining the flattening measured by Galeev et al., GCN8098 and Guidorzi et al., GCN8099), after which the light curve begins to decay more steeply with an index in the optical of alpha = 1.8 +/- 0.3. Hail, thunderstorm and heavy rain currently prevent further observations from the DK 1.54m. C. Thoene and C. Liebig acknowledge the excellent cheese fondue at the Swiss telescope yesterday evening.