Recurrence plot analysis of blazar gamma-ray light curves: Exploiting the time-domain capabilities of Fermi-LAT

TL;DR

This paper applies recurrence plot analysis to long-term gamma-ray light curves of blazars from Fermi-LAT, revealing potential nonlinearity and determinism in their variability, and introduces a new method for nonstationary time series analysis.

Contribution

It introduces the recurrence plot method for analyzing nonstationary gamma-ray light curves of blazars, enabling better characterization of their variability and jet dynamics.

Findings

Mkn 421 shows more determinism than PKS 1424-41.

Both sources potentially exhibit nonlinearity.

Recurrence analysis can be extended to a larger blazar sample.

Abstract

Variability studies of jetted AGN, in particular blazars, have been used to gain a better understanding of the particle acceleration mechanisms in jets. However, statistical methods used for the characterization of variability often rely on stationary time series data, which is not fulfilled for most blazar light curves. We introduce the recurrence plot method for long-term $\gamma$-ray light curves sampled by Fermi-LAT and present our results for the BL Lac object Mkn 421 and the FSRQ PKS 1424-41. Using surrogates to determine the significance of our findings, we conclude that Mkn 421 exhibits more determinism than PKS 1424-41, and that both sources potentially show nonlinearity. However, the latter has to be tested against more advanced surrogates that are able to replicate the nonstationarity of the original light curves. In future work, we will extend our recurrence analysis to a sample of $\sim50$ $\gamma$-ray bright sources to probe the jet dynamics of different blazar classes.