Gaussian Process Modeling Blazar Multiwavelength Variability: Indirectly Resolving Jet Structure

TL;DR

This study uses Gaussian process modeling to analyze long-term multiwavelength variability in blazars, revealing that jet variability is consistent across different energies and may be driven by the same physical process as accretion disks.

Contribution

The paper introduces a novel application of Gaussian process methods to compare thermal and nonthermal emissions in blazars, providing insights into jet structure and variability mechanisms.

Findings

Optical and gamma-ray timescales are statistically consistent.

Synchrotron and inverse-Compton emissions share the same power spectral density.

Jet variability timescales are similar to those of accretion disk emission.

Abstract

Blazar jet structure can be indirectly resolved by analyzing the multiwavelength variability. In this work, we analyze the long-term variability of blazars in radio, optical and X-ray energies with the Gaussian process (GP) method. The multiwavelength variability can be successfully characterized by the damped-random walk (DRW) model. The nonthermal optical characteristic timescales of 38 blazars are statistically consistent with the $\gamma$-ray characteristic timescales of 22 blazars. For three individuals (3C 273, PKS 1510-089, and BL Lac), the nonthermal optical, X-ray, and $\gamma$-ray characteristic timescales are also consistent within the measured 95$\%$ errors, but the radio timescale of 3C 273 is too large to be constrained by the decade-long light curve. The synchrotron and inverse-Compton emissions have the same power spectral density, suggesting that the long-term jet variability is irrelevant to the emission mechanism. In the plot of the rest-frame timescale versus black hole mass, the optical-$\gamma$-ray timescales of the jet variability occupy almost the same space with the timescales of accretion disk emission from normal quasars, which may imply that the long-term variabilities of the jet and accretion disk are driven by the same physical process. It is suggested that the nonthermal optical-X-ray and $\gamma$-ray emissions are produced in the same region, while the radio core which can be resolved by very-long-baseline interferometry locates at a far more distant region from the black hole. Our study suggests a new methodology for comparing thermal and nonthermal emissions, which is achieved by using the standard GP method.