Hard radio, spectra from reconnection regions in Galactic nuclei

Extremely flat and inverted radio spectra as observed in galactic nuclei an d BL Lac sources are still a challenge for fast-particle acceleration model s. Continuous acceleration by electric fields in reconnection regions can r esult in almost-constant particle distributions and therefore in inverted s ynchrotron spectra independent of the details of the injected spectra. Thes e spectra are calculated from a spatially averaged diffusion transport equa tion in momentum space that includes systematic momentum gains and losses a s well as finite particle-escape lifetimes.