Large-scale extragalactic jets powered by very-high-energy gamma rays.

Area of Science:

• Astrophysics
• High-energy astrophysics
• Plasma physics

Background:

• Nonthermal synchrotron emission from large-scale jets in radiogalaxies and quasars requires a continuous supply of relativistic electrons.
• The standard model posits in situ acceleration of electrons within the jets.
• This continuous electron production must occur over scales exceeding 100 kpc.

Purpose of the Study:

• To propose an alternative model for the origin of relativistic electrons in large-scale jets.
• To investigate the role of electromagnetic cascades in supplying these electrons.
• To challenge the necessity of in situ acceleration for explaining synchrotron emission.

Main Methods:

• Theoretical modeling of electromagnetic cascade development.
• Analysis of particle injection and propagation within relativistic jets.
• Comparison of cascade model predictions with observational constraints on synchrotron emission.

Main Results:

• Electromagnetic cascades initiated by extremely high-energy gamma rays can effectively produce relativistic electrons.
• These cascades can distribute electrons throughout the entire length of the jet.
• This provides a viable "nonacceleration" mechanism for supplying electrons.

Conclusions:

• The proposed electromagnetic cascade model offers a compelling alternative to in situ acceleration for explaining relativistic electrons in radiogalaxy and quasar jets.
• This mechanism can account for the observed nonthermal synchrotron emission over large scales.
• Further observational and theoretical work is needed to fully validate this nonacceleration scenario.