Multiwavelength variability power spectrum analysis of the blazars 3C 279 and PKS1510−089 on multiple timescales

Abstract

We present the results of variability power spectral density (PSD) analysis using multiwavelength radio to GeV\,γ-ray light curves covering decades/years to days/minutes timescales for the blazars 3C\,279 and PKS\,1510−089. The PSDs are modeled as single power-laws, and the best-fit spectral shape is derived using the `power spectral response' method. With more than ten years of data obtained with weekly/daily sampling intervals, most of the PSDs cover ∼2-4 decades in temporal frequency; moreover, in the optical band, the PSDs cover ∼6 decades for 3C\,279 due to the availability of intranight light curves. Our main results are the following: (1) on timescales ranging from decades to days, the synchrotron and the inverse Compton spectral components, in general, exhibit red-noise (slope ∼2) and flicker-noise (slope ∼1) type variability, respectively; (2) the slopes of γ-ray variability PSDs obtained using a 3-hr integration bin and a 3-weeks total duration exhibit a range between ∼1.4 and ∼2.0 (mean slope = 1.60±0.70), consistent within errors with the slope on longer timescales; (3) comparisons of fractional variability indicate more power on timescales ≤100\, days at γ-ray frequencies as compared to longer wavelengths, in general (except between γ-ray and optical frequencies for PKS 1510−089); (4) the normalization of intranight optical PSDs for 3C\,279 appears to be a simple extrapolation from longer timescales, indicating a continuous (single) process driving the variability at optical frequencies; (5) the emission at optical/infrared wavelengths may involve a combination of disk and jet processes for PKS\,1510−089.