TITLE: GCN CIRCULAR NUMBER: 11200 SUBJECT: GRB 100901A: multicolor photometry at Mt.Terskol DATE: 10/09/03 21:36:18 GMT FROM: Alexei Pozanenko at IKI, Moscow M. Andreev, A. Sergeev (Terskol Branch of Institute of Astronomy), A.Pozanenko (IKI), N. Parakhin, S. Velichko, N. Borachok (IC AMER) V. Petkov (Baksan Neutrino Observatory INR RAS) on behalf of larger GRB follow up collaboration report: We performed multicolor observations of the afterglow (Immler et al., GCN 11159; Guidorzi et al., GCN 11160; Ivanov et al., GCN 11161; Klunko et al., GCN 11162) of the Swift GRB 100901A (Immler et al., GCN 11159) with the Zeiss-2000 and Meade-35 telescopes of Mt.Terskol of the first day after burst onset. The afterglow photometry is based on several reference stars of SDSS DR7 and Lupton transformation ugri -> BV: T0+ Filter, OT (d) Telescope: Meade-35 0.3527 V 17.80+/-0.05 Telescope: Zeiss-2000 0.3704 B 18.11+/- 0.02 0.4490 B 18.45+/- 0.02 0.4579 V 18.06+/- 0.02 0.4634 r(Gunn) 17.85+/- 0.02 0.4714 g(Gunn) 18.37+/- 0.02 The photometry is still preliminary and can be updated later.