A Novel Approach to Study the Variability of NGC 5548

A Bewketu Belete,J R De Medeiros,I C Leão,L J Goicoechea,B L Canto Martins

doi:10.3847/1538-4357/ab2457

A Bewketu Belete, J R De Medeiros + Show 3 more

Open Access

https://doi.org/10.3847/1538-4357/ab2457

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Abstract

Abstract Understanding the properties of the continuum radiation and broad emission lines of active galactic nuclei provides significant information not only to model the radiation mechanism and constrain the geometry and kinematics of the broad-line region (BLR) but also to probe the central engine of the sources. Here we investigate the multifractal behavior of the Hβ emission line and the 5100 Å continuum flux light curves of NGC 5548. The aim is to search for multiscaling signatures in the light curves and check if there is a possible nonlinear relationship between them. To this end, we use a multifractality analysis technique called the Multifractal Detrended Moving Average analysis. We detect multifractal (nonlinear) signatures in the full monitoring and densely sampled period of the Hβ line and 5100 Å continuum light curves of NGC 5548, possibly indicating the presence of complex and nonlinear interaction in the 5100 Å continuum and Hβ emission line regions. Moreover, the degree of multifractality of the Hβ line is found to be about twice that of the 5100 Å continuum. The nonlinearity of both emissions could be generated when the BLR reprocesses the radiation from the central compact source. Finally, we found that antipersistent long-range temporal correlation is the main source of the multifractality detected in both light curves.

Highlights

In the study of active galactic nuclei, understanding the nature of the central engine, the geometry and kinematics of the broad-line region, and the connection between the continuum and the BLR remain the most important questions
If not all, AGNs consist of mainly four important regions: the central engine, the continuum region, the BLR, and the narrow-line region (NLR)
It has been recognized that knowledge about the variations in the broad emission lines of quasars provides us with valuable information that can be used to constrain the size of the BLR and the continuum region (e.g., Lewis & Ibata 2004)

Summary

Introduction

In the study of active galactic nuclei (hereinafter AGNs), understanding the nature of the central engine, the geometry and kinematics of the broad-line region (hereinafter BLR), and the connection between the continuum and the BLR remain the most important questions. The technique based on the lag between the intrinsic variability of the continuum and of the broad emission lines, reverberation mapping, has been applied in studying the geometry and kinematics of the BLR (e.g., Peterson 1993, 2006; Gondhalekar et al 1994; Bon et al 2018; Lira et al 2018). Though it has been applied largely following its success, the reverberation mapping technique of determining the size of BLR continues to have several limitations (e.g., Guerras et al 2013 and the references therein)

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