TITLE: GCN CIRCULAR NUMBER: 17315 SUBJECT: GRB 150120B: P60 optical afterglow DATE: 15/01/20 08:11:39 GMT FROM: Daniel Perley at Caltech D. A. Perley (Caltech) reports on behalf of a larger collaboration: The Palomar 60-inch robotic telescope began automatic follow-up of the location of GRB 150120B (D'Elia et al., GCN 17314) starting at 07:26:07 UT on 2015-01-20. In the first three 60-second frames (r, i, and z-bands) we detect a bright (r~18.7 mag), new source at the following location (J2000): RA = 02:37:09.770 dec = +08:04:40.37 After these three frames, the telescope received the initial XRT position notice and it executed a large slew to a new position, and this optical source was no longer in the field of view. It returned to the field with the updated XRT position notice in an image starting at 07:47:47; the GRB afterglow shows significant fading (to r~19.7 mag) in this observation since the first epoch, confirming it as the optical afterglow. We also note that the optical position above is near, but significantly outside (7 arcsec west) of, the updated XRT position given in GCN 17314. [GCN OPS NOTE(20jan15): Per author's request, the GRB name in the Subject-line was changed from 140120B to 150120B.]