TITLE: GCN CIRCULAR NUMBER: 17530 SUBJECT: GRB 150301B: LCOGT-Sutherland observations DATE: 15/03/02 09:00:17 GMT FROM: Cristiano Guidorzi at Ferrara U,Italy C. Guidorzi (U. Ferrara), J. Japelj, A. Gomboc (U. Ljubljana), C.G. Mundell (U. Bath), on behalf of a large collaboration report: One of the Las Cumbres Observatory 1-m telescopes in Sutherland (South Africa) began observing Swift and Fermi GRB 150301B (Lien et al. GCN 17515; Burns et al. GCN 17525) on March 01 at 20:07:30 UT, i.e. ~29.4 minutes after the BAT trigger with the r', i', and g' filters. We detect the optical afterglow (Lien et al. GCN 17515; Buckley et al. GCN 7518; Kann et al. GCN 17522; de Ugarte Postigo et al. GCN 17523) with the following magnitudes: Mid time from Total Exp Filter Magnitude trigger (min) (s) ------------------------------------------------- 37.7 360 r' 18.85 +- 0.25 42.3 360 i' 18.5 +- 0.3 ------------------------------------------------- Values have been calibrated against nearby USNOB-1 stars (R2 and I). Compared with earlier (Buckley et el.) and later (Kann et al.) observations, our values suggest an overall power-law decay index ~1.