TITLE: GCN CIRCULAR NUMBER: 15191 SUBJECT: GRB 130907A: Skynet DSO-14/Yerkes-41 detections of a possible afterglow DATE: 13/09/08 02:40:43 GMT FROM: Adam S. Trotter at UNC-Chapel Hill/PROMPT/Skynet A. Trotter, J. Haislip, A. LaCluyze, J. Moore, N. Frank, D. Reichart, A. Smith, D. Caton, L. Hawkins, V. Hoette, D. Harper, R. Kron, K. Cudworth, E. Struble, R. Russell, T. Linder, T. Berger, H. T. Cromartie, R. Egger, A. Foster, K. Ivarsen, M. Maples, M. Nysewander, and J. A. Crain report: Skynet observed 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). Starting at 2013-09-08, 00:43 UT (t=3.03h post-trigger) and continuing until 17:41 UT (t=35.5m-4.65h post-trigger), Skynet took a total of 42 160s exposures. We detect an uncatalogued optical source in stacked images at RA 14:23:34.03, Dec +45:36:26.7 (J2000.0), consistent with the afterglow position reported by de Ugarte Postigo et al. (GCN 15187), and ~8" south of the Swift-XRT localization. At t=3.4h post-trigger, R~19.6 mag. The time range of our observations is not sufficient to confirm whether the source is indeed fading. A preliminary light curve is at: http://skynet.unc.edu/grb/grb130907a.png R and I magnitudes are in the Vega system, and r' and i' 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). Skynet observations are ongoing.