Radio-loud and radio-quiet quasars: one population, different epochs of observation

TL;DR

This paper reviews evidence that quasars' radio emission varies rapidly and intermittently, suggesting radio-loudness depends on the epoch of observation, and introduces a new model for radio-quiet quasar core emission.

Contribution

It synthesizes evidence for episodic jet activity and proposes a new model for radio-quiet quasar core emission, emphasizing the importance of observation epoch.

Findings

Radio synchrotron lobes fade rapidly after ejection

Jet activity in quasars is intermittent and episodic

A new model explains weak core radio emission in radio-quiet quasars

Abstract

I bring together evidence for the rapidity with which quasars' radio synchrotron lobe emission fades and for the intermittency with which jet plasma is ejected from individual quasars and radio galaxies and affirm the picture presented by Nipoti et al (2005) that the radio-loudness of quasars is a function of the epoch at which they are observed. I briefly illustrate this account with examples of successive episodes of jet activity where the axis along which jet plasma is launched appears to have precessed. A new model for the weak core radio emission from radio-quiet quasars, that is not any kind of jet ejecta, is also briefly described.