A Comprehensive Power Spectral Density Analysis of Astronomical Time Series. I. The FermiLAT GammaRay Light Curves of Selected Blazars
Abstract
We present the results of the FermiLarge Area Telescope 10 yr long light curve (LC) modeling of selected blazars: six flatspectrum 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, LombScargle periodogram (LSP), wavelet scalogram, autoregressive moving average (ARMA) process, continuoustime ARMA (CARMA), Hurst exponent (H), and the ${ \mathcal A }\mbox{}{ \mathcal T }$ 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 powerlaw indices β calculated from the Fourier and LSP modeling mostly fall in the range 1 ≲ β ≲ 2. Using the wavelet scalograms, we confirm a quasiperiodic oscillation (QPO) in PKS 2155304 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 longterm memory. Finally, the FSRQ and BL Lac subclasses are clearly separated in the ${ \mathcal A }\mbox{}{ \mathcal T }$ plane.
 Publication:

The Astrophysical Journal Supplement Series
 Pub Date:
 September 2020
 DOI:
 10.3847/15384365/aba2c7
 arXiv:
 arXiv:2006.03991
 Bibcode:
 2020ApJS..250....1T
 Keywords:

 Active galactic nuclei;
 Blazars;
 Light curves;
 Time series analysis;
 High energy astrophysics;
 BL Lacertae objects;
 Quasars;
 16;
 164;
 918;
 1916;
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 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Astrophysics of Galaxies;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 59 pages, 23 figures, 7 tables