TITLE: GCN CIRCULAR NUMBER: 18703 SUBJECT: GRB151215A: Early optical light curve from pt5m, La Palma DATE: 15/12/16 15:03:14 GMT FROM: Liam K Hardy at U of Shffield L. K. Hardy (Sheffield), S. P. Littlefair (Sheffield), V. S. Dhillon (Sheffield, IAC), T. Butterley (Durham) and R. W. Wilson (Durham) report: The automated robotic telescope 'pt5m' (Hardy et al. 2015, MNRAS 454, 4316) on La Palma observed the field of GRB 151215A (Gibson et al., GCN 18691) starting at 03:02:42 UT on Dec 15, 53 seconds after the alert notice release and 74 seconds after the GRB detection. Observations comprised of 59 x 60-second exposures in the Johnson/Cousins R-band with approximately 6-seconds dead time between images. The final image was taken 65 minutes after the first. We detect the optical counterpart to the GRB and observe a rapidly declining light curve. Photometry is performed using historical instrumental zeropoints. We measure an initial magnitude of R = 17.13 +/- 0.04 (2 minutes after the GRB) and a final magnitude of R = 20.8 +/- 0.7 (67 minutes after the GRB). The light curve is available at: http://slittlefair.staff.shef.ac.uk/images/grb151215.png