Methods of Reverberation Mapping. I. Time-lag Determination by Measures of Randomness

TL;DR

This paper introduces a new method for measuring time delays in quasar reverberation mapping using measures of randomness, which is effective for irregularly sampled data and does not rely on complex modeling.

Contribution

It presents an optimized von Neumann-based scheme for time-lag determination that outperforms existing correlation methods and requires fewer assumptions about variability processes.

Findings

The method accurately recovers known time delays in quasar data.

It handles sparse and irregular sampling effectively.

The size-luminosity relation of the broad-line region is confirmed with less assumption.

Abstract

A class of methods for measuring time delays between astronomical time series is introduced in the context of quasar reverberation mapping, which is based on measures of randomness or complexity of the data. Several distinct statistical estimators are considered that do not rely on polynomial interpolations of the light curves nor on their stochastic modeling, and do not require binning in correlation space. Methods based on von Neumann's mean-square successive-difference estimator are found to be superior to those using other estimators. An optimized von Neumann scheme is formulated, which better handles sparsely sampled data and outperforms current implementations of discrete correlation function methods. This scheme is applied to existing reverberation data of varying quality, and consistency with previously reported time delays is found. In particular, the size-luminosity relation of the broad-line region in quasars is recovered with a scatter comparable to that obtained by other works, yet with fewer assumptions made concerning the process underlying the variability. The proposed method for time-lag determination is particularly relevant for irregularly sampled time series, and in cases where the process underlying the variability cannot be adequately modeled.