A Minimal Stochastic Variability Model of Blazars in Turbulent Cascade

TL;DR

This paper introduces a minimal physical model based on turbulent cascade processes in magnetized jets to explain the universal stochastic variability observed in blazars, aligning well with various observational features.

Contribution

The model offers a new physical framework for blazar variability, emphasizing turbulence and energy transfer without complex particle acceleration or cooling details.

Findings

Reproduces the universal power spectral density (PSD) structure of blazars.

Explains the steeper high-frequency PSD slope observed in AGN variability.

Matches observed fractional variability amplitude (FVA) characteristics.

Abstract

In this paper, we propose a novel minimal physical model to elucidate the long-term stochastic variability of blazars. The model is built on the realistic background of magnetized plasma jets dissipating energy through a turbulent cascade process that transfers energy to small-scale structures with highly anisotropic radiation. The model demonstrates the ability to spontaneously generate variability features consistent with observations of blazars under uniformly random fluctuations in the underlying physical parameters. This indicates that the model possesses self-similarity across multiple time scales, providing a natural explanation for the universal power spectral density (PSD) structure observed in different types of blazars. Moreover, the model exhibits that when the cascade process produces a relatively flat blob energy distribution, the spectral index of the model-simulated PSD in the high-frequency regime will be steeper than that predicted by the Damped Random Walk (DRW) model, which is in agreement with recent observations of active galactic nucleus (AGN) variability, providing a plausible theoretical explanation. The model is also able to reproduce the observed fractional variability amplitude (FVA) characteristics of blazars, and suggests that the specific particle acceleration and radiative cooling processes within the blob may not be the key factor shaping the long-term stochastic variability. This minimal model provides a new physical perspective for understanding the long-term stochastic variability of blazars.