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

Published online by Cambridge University Press:  24 March 2015

M. Sobolewska ,
A. Siemiginowska ,
B. Kelly  and
K. Nalewajko
M. Sobolewska
Affiliation:
Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland email: [email protected]
A. Siemiginowska
Affiliation:
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
B. Kelly
Affiliation:
Department of Physics, Broida Hall, University of California, Santa Barbara, CA 93106-9530, USA
K. Nalewajko
Affiliation:
Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, Stanford University, 2575 Sand Hill Road M/S 29, Menlo Park, CA 94025, USA NASA Einstein Postdoctoral Fellow
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Abstract

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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.

Keywords

black hole physicsBL Lacertae objects: generalgalaxies: activegalaxies: jetsgamma rays: galaxies
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 10 , Issue S313: Extragalactic jets from every angle , September 2014 , pp. 21 - 26
Copyright
Copyright © International Astronomical Union 2015 

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