Bottom-up modelling of gamma-ray AGNs

I discuss the role of radio observations and modelling of the low-frequency emission in active galactic nuclei (AGN). I emphasise the significance of the synchrotron spectrum in understanding the sources and modelling their gamma-ray emission. I discuss some of the AGN-specific parts of the Planck early-release data analysis published elsewhere [1]. The focus of the discussion is on modelling the blazar spectral energy distribution and gamma-ray variability using a "bottom-up" approach, from the point of view of the radiating particles, emphasising the role of low-energy emission in determining the parameters and conditions responsible for the high-energy emission.