Flat-spectrum radio sources: cosmic conspiracy or relativistic neutrons?

Abstract

RADIO-LOUD active galactic nuclei (AGNs) tend to show extended emission in the form of jets and an unresolved central core, from which the jets presumably originate. The intensity spectrum of the core varies smoothly from 10^8.5 to 10¹⁶ Hz in frequency¹, and is flat (constant with frequency) between 10⁹ and 10¹² Hz, implying that a single emission mechanism, probably synchrotron radiation, is responsible. Because synchrotron emission below ∼10^l3Hz would be self-absorbed for a uniform source under conditions typical of AGNs, inhomogeneous models have been used to account for these spectra. These models, which require the magnetic field strength and the electron density and energy to vary according to strict power laws, reproduce the flat spectra by a number of self-absorbed components^2–4, but they do not explain the origin of radiating electrons at ∼10¹⁸ cm from the AGN core, in view of the very short lifetime of the electrons in an AGN environment. Here we propose that energy is transported from the central source by relativistic neutrons, which travel freely over a large volume and decay into relativistic protons. The protons produce secondary electrons which generate the observed radiation. The photon spectra thus produced are largely model independent and flat.