GCN Circular 18273
WeiKang Zheng, Alexei V. Filippenko and Heechan Yuk (UC Berkeley), Yinan Zhu (NAOC) and Daniel A. Perley (Dark Cosmology Center) report on behalf of the KAIT GRB team: We observed the optical afterglow of GRB 150910A (Pagani et al., GCN 18264; Zheng & Filippenko, GCN 18265) with the Kast spectrograph on the 3m Shane telescope at Lick Observatory, started at 10:08 UT (about 1.1 hours after the burst), covering the 3500 - 10000 A wavelength range. A 1200-second and a 2400-second exposures were acquired. The spectrum shows blue continuum flux across the entire spectral range. We detect absorption lines from Mg II (2796,2803) and Fe II (2344,2374,2383) at a common redshift of z=1.359, as well as additional lines further to the blue. We suggest this as the likely redshift of the GRB.