The flux distribution of individual blazars as a key to understand the dynamics of particle acceleration

TL;DR

This paper demonstrates that linear Gaussian fluctuations in particle acceleration or escape timescales can produce non-Gaussian flux distributions in blazars, helping to identify the micro-physical origins of their variability.

Contribution

It shows that simple linear Gaussian variations can explain complex flux distributions, providing a new method to understand particle acceleration mechanisms in blazars.

Findings

Gaussian fluctuations in acceleration explain flux variability in Mkn 421

Flux distributions can reveal micro-physical variability origins

Spectral index distributions support the acceleration variability model

Abstract

The observed log-normal flux distributions in the high energy emission from blazars have been interpreted as being due to variability stemming from non-linear multiplicative processes generated dynamically from the accretion disc. On the other hand, rapid minute scale variations in the flux point to a compact emitting region inside the jet, probably disconnected from the disc. In this work, we show that linear Gaussian variations of the intrinsic particle acceleration or escape time-scales can produce distinct non-Gaussian flux distributions, including log-normal ones. Moreover, the spectral index distributions can provide confirming evidence for the origin of the variability. Thus, modelling of the flux and index distributions can lead to quantitative identification of the micro-physical origin of the variability in these sources. As an example, we model the X-ray flux and index distribution of Mkn 421 obtained from over 9 years of MAXI observations and show that the variability in the X-ray emission is driven by Gaussian fluctuations of the particle acceleration process rather than that of the escape rate.