Program: GN-2013B-Q-60

In Faranoff-Riley type II (FRII) radio galaxies the jets extending from the nucleus remain well-collimated over long distances and terminate in a shock upon encountering the denser intergalactic medium. In the shock regions, commonly referred to as hotspots, jet particles get re-accelerated and emit over a range of frequencies, spanning from the radio- to the X-Ray bands. The emission mechanism can either be synchrotron radiation or inverse-Compton scattering (IC). Cygnus A (3C405) is the closest, powerful FRII radio galaxy, it has been studied extensively in radio and X-Rays, but optical and NIR data are scarce. We propose to obtain deep optical and NIR images of the hotspot regions in Cygnus A, with the aim to identify the hotspot counterparts. Measuring the optical and NIR hotspot fluxes will allow us to bridge the gap between existing radio and X-Ray data and construct a full, spatially resolved and astrometric accurate spectral energy distribution (SED) of the emitting electron population. The slope of the full SED will then be used to identify the emission mechanism and, in case of IC emission, used to directly measure the underlying magnetic field strength. In turn, this will allow us to calculate the energy contained in the hotspots and the energy injected in the radio lobes, improving our understanding of radio galaxy evolution and the impact on their immediate surroundings.