TITLE: GCN CIRCULAR NUMBER: 11066 SUBJECT: GRB 100805A: IAC80 and 1.5m OSN optical observations DATE: 10/08/06 17:24:14 GMT FROM: Javier Gorosabel at IAA-CSIC J. Gorosabel (IAA-CSIC, Granada), M. Chioare Diaz-Martin (IAC, Obs. del Teide, Tenerife), R. Iglesias Marzoa (Univ. of La Laguna, Tenerife), A. Sota (IAA-CSIC, Granada), A.J. Castro-Tirado (IAA-CSIC, Granada), J.M. Castro Cerón (ESAC, Madrid), report on behalf of a larger collaboration: "We observed the field of GRB 100805A (Hoversten et al., GCNC 11047) with the 0.82m IAC80 (Obs. of Teide, Tenerife, Spain) and 1.5m OSN (Obs. of Sierra Nevada, Granada, Spain) telescopes in VRI-bands. The observations were carried out on Aug 6.0515-6.1393 UT (IAC80) and Aug 6.1608-6.1875 UT (1.5m OSN), respectively. The optical afterglow is marginally detected in our images with a preliminary magnitude of R~21.5, calibrated against USNO-B1.0 field stars."