Lognormal variability in BL Lacertae

TL;DR

This paper reports the first detection of lognormal X-ray variability in the blazar BL Lac, suggesting a link between accretion disk activity and jet behavior, with variability amplitude proportional to flux.

Contribution

It demonstrates that BL Lac exhibits lognormal X-ray flux variability, a feature previously observed in other compact systems, indicating a possible connection between accretion processes and jet emissions.

Findings

Flux variations follow a lognormal distribution.

Variability amplitude scales with flux level.

BL Lac shows less variability compared to other blazars.

Abstract

X-ray data from the blazar BL Lac are used to investigate the nature of its variability, and more precisely the flux dependency of the variability and the distribution of fluxes. The variations in the flux are found to have a lognormal distribution and the average amplitude of variability is proportional to the flux level. BL Lac is the first blazar in which lognormal X-ray variability is clearly detected. Lognormal variability in X-ray light curves, probably related to accretion disk activity, has been discovered in various compact systems, such as Seyfert galaxies and X-ray binaries. The light curve is orders of magnitude less variable than other blazars, with few bursting episodes. If this defines a specific state of the source, then the lognormality might be the imprint of the accretion disk on the jet, linking for the first time accretion and jet properties in a blazar.