Time Series Analysis of Active Galactic Nuclei: The case of Arp 102B, 3C 390.3, NGC 5548 and NGC 4051

TL;DR

This study compares two time series analysis methods, ZDCF and SPEAR, on AGN emission lines to measure time lags, revealing correlations with line properties and implications for black hole mass estimates.

Contribution

It introduces a comparative analysis of ZDCF and SPEAR methods for AGN reverberation mapping, highlighting their correlation and impact on black hole mass estimation.

Findings

Hβ lags are larger than Hα for some AGNs, suggesting emission at larger radii.

ZDCF and SPEAR time lags are highly correlated (r ~ 0.87).

Uncertainty in black hole mass estimates increases with line broadening.

Abstract

We used the Z-transformed Discrete Correlation Function (ZDCF) and the Stochastic Process Estimation for AGN Reverberation (SPEAR) methods for the time series analysis of the continuum and the H${\alpha}$ and H${\beta}$ line fluxes of a sample of well known type 1 active galactic nuclei (AGNs): Arp 102B, 3C 390.3, NGC 5548, and NGC 4051, where the first two objects are showing double-peaked emission line profiles. The aim of this work is to compare the time lag measurements from these two methods, and check if there is a connection with other emission line properties. We found that the obtained time lags from H$\beta$ are larger than those derived from the H$\alpha$ analysis for Arp 102B, 3C 390.3 and NGC 5548. This may indicate that the H$\beta$ line originates at larger radii in these objects. Moreover, we found that the ZDCF and SPEAR time lags are highly correlated ($r \sim0.87$), and that the error ranges of both ZDCF and SPEAR time lags are correlated with the FWHM of used emission lines ($r\sim 0.7$). This increases the uncertainty of the black hole mass estimates using the virial theorem for AGNs with broader lines.