Stochastic approach to modeling the γ-ray variability of Fermi/LAT blazars

• Published in: Proceedings of the International Astronomical Union Vol. 10; no. S313; pp. 21 - 26
• Main Authors: Sobolewska, M., Siemiginowska, A., Kelly, B., Nalewajko, K.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 01.09.2014
• Subjects: Astronomical instruments; Blazars; Contributed Papers; Density; Mathematical models; Sky surveys (astronomy); Slopes; Spectra; Time; BL Lacertae objects: general; gamma rays: galaxies; black hole physics; galaxies: jets; galaxies: active
• ISSN: 1743-9213; 1743-9221
• DOI: 10.1017/S1743921315001805

We studied the γ-ray variability of 13 blazars observed with the Fermi Large Area Telescope (LAT). These blazars were among the brightest ones monitored during the first 4 years of the Fermi sky survey. We modelled their γ-ray light curves with the Ornstein-Uhlenbeck (OU) process or mixed OU process. The power spectral density (PSD) of the OU process is a zero-centered Lorentzian function, proportional to 1/fα with α changing at a characteristic time scale, τ0, from 0 (τ ≫ τ0) to 2 (τ ≪ τ0). The PSD of the mixed OU process has in addition an intermediate part with 0 < α < 2 between the long and short characteristic time scales. We show that the OU model provides a good description of the Fermi/LAT light curves of three blazars in our sample. For the first time we provide constraints on the characteristic γ-ray time scale of variability in two BL Lac sources, 3C 66A and PKS 2155-304. We find that the mixed OU process describes the light curves of the remaining 10 blazars better than the OU process. We infer that their Fermi/LAT PSD resemble power-law functions and constrain their PSD slopes.