Gaussian Process Modeling Blazar Multiwavelength Variability: Indirectly Resolving Jet Structure

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 model. The nonthermal optical characteristic timescales of 38 blazars are statistically consistent with the γ -ray characteristic timescales of 22 blazars. For three individual sources (3C 273, PKS 1510-089, and BL Lac), the nonthermal optical, X-ray, and γ -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- γ -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 γ -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.

Keywords

• Blazars
• Jets
• Light curves
• Time series analysis