Charge-starved, relativistic jets and blazar variability

TL;DR

This paper proposes a mechanism involving large-amplitude waves in charge-starved, relativistic jets to explain rapid blazar variability, linking jet acceleration and small-scale structures to black-hole magnetosphere conditions.

Contribution

It introduces a new model based on wave propagation in charge-starved jets that accounts for jet acceleration and rapid variability in blazars, emphasizing the role of pair multiplicity.

Findings

Delayed jet acceleration begins around 1 parsec from the black hole.

Rapid variability is linked to low pair multiplicity in the magnetosphere.

Wave-driven structures modulate high-energy emission in blazars.

Abstract

High energy emission from blazars is thought to arise in a relativistic jet launched by a supermassive black hole. The emission site must be far from the hole and the jet relativistic, in order to avoid absorption of the photons. In extreme cases, rapid variability of the emission suggests that structures of length-scale smaller than the gravitational radius of the central black hole are imprinted on the jet as it is launched, and modulate the radiation released after it has been accelerated to high Lorentz factor. We propose a mechanism which can account for the acceleration of the jet, and for the rapid variability of the radiation, based on the propagation characteristics of large-amplitude waves in charge-starved, polar jets. Using a two-fluid (electron-positron) description, we find the outflows exhibit a delayed acceleration phase, that starts at roughly 1pc, where the inertia associated with the wave currents becomes important. The time-structure imprinted on the jet at launch modulates photons produced by the accelerating jet provided the pair multiplicity in the black-hole magnetosphere is sufficiently small, suggesting that very rapid variability is confined to sources in which the electromagnetic cascade in the black-hole magnetosphere is not prolific.