From Clark Lake to Chandra: Closing in on the Low End of the Relativistic Electron Spectra in Extragalactic Sources

Abstract

The limited angular resolutions and sensitivities historically available below 300 MHz have made it difficult to define the low end of the electron energy distribution, N(gamma). We extrapolate down from the well observed segments of radio spectra with almost complete ignorance of what N(gamma) is actually doing. We do not know if there is a low energy cutoff or if there are other deviations from extrapolated power laws. The result is that we really do not have a good estimate of the total energy density and pressure of the relativistic plasmas we study. The situation is even worse for Inverse Compton (IC) X-ray emission, several flavors of which rely on electrons of Lorentz factors, gamma, of 1000, 300, or in some cases of order 50. If our assumed extrapolations are wrong, some IC emission models may have to be abandoned. We present several examples and demonstrate that the Long Wave Array (LWA) should have sufficient sensitivity and resolution to obtain meaningful constraints on N(gamma) at low energies.