To be published in "The Starburst-AGN Connection" 2001.
astro-ph/0109495

For a postscript version of the article, click here.

Abstract. Continuum and emission-line variability of active galactic nuclei provides a powerful probe of microarcsecond scale structures in the central regions of these sources. In this contribution, we review basic concepts and methodologies used in analyzing AGN variability. We develop from first principles the basics of reverberation mapping, and pay special attention to emission-line transfer functions. We discuss application of cross-correlation analysis to AGN light curves. Finally, we provide a short review of recent important results in the field.

Table of Contents

• INTRODUCTION
• BACKGROUND AND BASIC PHENOMENOLOGY
• Basic Characteristics of Variability
• Origin of the Variations
• Blazar Variability
• Emission-Line Variability
• The First Monitoring Programs
• Spectrophotometric Flux Calibration
• Requirements for a Successful Monitoring Program
• THEORY OF REVERBERATION MAPPING
• Reverberation Mapping Assumptions
• The Transfer Equation
• Isodelay Surfaces
• Transfer Functions for a Variety of Simple Models
• Transfer Function Recovery
• CROSS-CORRELATION ANALYSIS
• Fundamentals
• Relationship to the Transfer Function
• Discrete Correlation Methods
• Computational Issues
• Uncertainties in Cross-Correlation Lags
• OBSERVATIONAL RESULTS
• Size of the Broad-Line Region
• AGN Black-Hole Masses
• Emission-Line Transfer Functions
• Emission-Line Profile Variability
• Multiwavelength Continuum Variability
• Conclusion
• REFERENCES