Duration of the active phase in episodic radio galaxies

Determine the duration of the active phase of AGN jet activity in radio galaxies that undergo multiple episodes of jet launching (for example, restarted radio galaxies and double-double radio galaxies), to inform assessments of nuclear activity duty cycles.

Background

The paper discusses that some radio galaxies do not exhibit a single continuous episode of jet activity, but instead show evidence for multiple, distinct episodes separated by quiescent periods. In such systems, inner lobes trace recent activity while outer lobes retain relic signatures of past activity, observable especially at low radio frequencies due to the long synchrotron lifetimes of low-energy electrons.

Understanding how long a single active phase persists is central to characterizing AGN duty cycles. In J1007+3540, the authors measure radiative ages for different components (inner lobes ~140 Myr; outer lobe/backflow ~240–260 Myr), highlighting episodic behavior but not resolving the general question of the typical duration of an active phase across episodic radio galaxies. Establishing these timescales would link jet energetics, environmental influences, and AGN fueling histories.