A Comprehensive Power Spectral Density Analysis of Astronomical Time Series. I. The Fermi-LAT Gamma-Ray Light Curves of Selected Blazars

DOI: 
10.3847/1538-4365/aba2c7
Publication date: 
01/09/2020
Main author: 
Tarnopolski, Mariusz
IAA authors: 
Pascual-Granado, Javier
Authors: 
Tarnopolski, Mariusz;Żywucka, Natalia;Marchenko, Volodymyr;Pascual-Granado, Javier
Journal: 
The Astrophysical Journal Supplement Series
Refereed: 
Yes
Publication type: 
Article
Volume: 
250
Pages: 
1
Abstract: 
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 ${ \mathcal A }\mbox{--}{ \mathcal T }$ 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 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 ${ \mathcal A }\mbox{--}{ \mathcal T }$ plane.
Database: 
ADS
SCOPUS
URL: 
https://ui.adsabs.harvard.edu/#abs/2020ApJS..250....1T/abstract
ADS 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;739;158;1319