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2020ApJS..250....1T - Astrophys. J., Suppl. Ser., 250, 1-1 (2020/September-0)

A comprehensive power spectral density analysis of astronomical time series. I. The Fermi-LAT gamma-ray light curves of selected blazars.

TARNOPOLSKI M., ZYWUCKA N., MARCHENKO V. and PASCUAL-GRANADO J.

Abstract (from CDS):

We present the results of the Fermi-Large Area Telescope 10 yr long light curve (LC) modeling of selected blazars: six flat-spectrum radio quasars (FSRQs) and five BL Lacertae (BL Lacs), examined in 7, 10, and 14 day binning. The LCs and power spectral densities (PSDs) were investigated with various methods: Fourier transform, Lomb-Scargle periodogram (LSP), wavelet scalogram, autoregressive moving average (ARMA) process, continuous-time ARMA (CARMA), Hurst exponent (H), and the A – T plane. First, with extensive simulations we showed that parametric modeling returns unreliable parameters, with a high dispersion for different realizations of the same stochastic model. Hence, any such analysis should be supported with Monte Carlo simulations. For our blazar sample, we find that the power-law indices β calculated from the Fourier and LSP modeling mostly fall in the range 1 <= β <= 2. Using the wavelet scalograms, we confirm a quasi-periodic oscillation (QPO) in PKS 2155-304 at a 3σ significance level, but do not detect any QPOs in other objects. The ARMA fits reached higher orders for 7 day binned LCs and lower orders for 10 and 14 day binned LCs for the majority of blazars, suggesting there might exist a characteristic timescale for the perturbations in the jet and/or accretion disk to die out. ARMA and CARMA modeling revealed breaks in their PSDs at timescales of a few hundred days. The estimation of H was performed with several methods. We find that most blazars exhibit H > 0.5, indicating long-term memory. Finally, the FSRQ and BL Lac subclasses are clearly separated in the A – T plane.

Abstract Copyright: © 2020. The American Astronomical Society. All rights reserved.

Journal keyword(s): Active galactic nuclei - Blazars - Light curves - Time series analysis - High energy astrophysics - BL Lacertae objects - Quasars

Simbad objects: 17

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2021.03.09-10:10:36

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