TITLE: GCN CIRCULAR NUMBER: 15193 SUBJECT: GRB 130907A: Skynet DSO-14/Yerkes-41/GORT confirmation of a fading afterglow DATE: 13/09/08 06:28:32 GMT FROM: Adam S. Trotter at UNC-Chapel Hill/PROMPT/Skynet A. Trotter, D. Reichart, J. Haislip, A. LaCluyze, K. McLin, L. Cominsky, A. B. Smith, D. Caton, L. Hawkins, V. Hoette, K. Cudworth, D. Harper, R. Kron, T. Linder, R. Russell, E. Struble, T. Berger, H. T. Cromartie, R. Egger, A. Foster, N. Frank, K. Ivarsen, M. Maples, J. Moore, M. Nysewander, and J. A. Crain report: In Trotter et al. (GCN 15191), we reported Skynet observations of the Swift/XRT localization of GRB 130907A (Page et al., GCN 15183, Swift trigger 569992) with the 14" telescope at the Appalachian State University Dark Sky Observatory (DSO-14) in NC, USA (R and I bands), and with the 41" telescope of Yerkes Observatory in WI, USA (r' and i' bands). Skynet continued observing the field with the 14" GLAST Optical Robotic Telescope (GORT) at the Hume observatory in CA, USA. From t=5.9h - 8.2h post-trigger, GORT took a total of 54x160s exposures in the R and I bands. We confirm a fading afterglow at the position reported by de Ugarte Postigo et al. (GCN 15187) and by Lee et al. (GCN 15192). The afterglow fades from I=18.1 mag at t=3.2h to I=19.2 mag at t=8.2h, consistent with a power-law index alpha~-0.9. A preliminary light curve is at: http://skynet.unc.edu/grb/grb130907a_2.png R and I magnitudes are in the Vega system, and r' and i' magnitudes are in the AB system, calibrated to 5 APASS stars in the field. Magnitudes have not been corrected for line-of-sight Milky Way dust extinction, with expected E(B-V)=0.011 (Schlegel et al. 1998). No further Skynet observations are scheduled.