Using Leaked Power to Measure Intrinsic AGN Power Spectra of Red-Noise Time Series

TL;DR

This paper introduces a new method using the normalized leakage spectrum (NLS) to accurately measure the intrinsic high-frequency power spectra of AGN variability, overcoming biases caused by red-noise leakage and gaps in data.

Contribution

The study develops a novel NLS approach that effectively constrains the intrinsic AGN PSD by accounting for red-noise leakage effects, validated through Monte Carlo simulations.

Findings

NLS sensitively reflects the underlying PSD under severe red-noise leakage.

The method accurately constrains the intrinsic high-frequency PSD of AGNs.

Monte Carlo simulations confirm the effectiveness of the NLS approach.

Abstract

Fluxes emitted at different wavebands from active galactic nuclei (AGNs) fluctuate at both long and short timescales. The variation can typically be characterized by a broadband power spectrum, which exhibits a red-noise process at high frequencies. The standard method of estimating power spectral density (PSD) of AGN variability is easily affected by systematic biases such as red-noise leakage and aliasing, in particular, when the observation spans a relatively short period and is gapped. Focusing on the high-frequency PSD that is strongly distorted due to red-noise leakage and usually not significantly affected by aliasing, we develop a novel and observable normalized leakage spectrum (NLS), which describes sensitively the effects of leaked red-noise power on the PSD at different temporal frequencies. Using Monte Carlo simulations, we demonstrate how an AGN underlying PSD sensitively determines the NLS when there is severe red-noise leakage and thereby how the NLS can be used to effectively constrain the underlying PSD.