Time variability provides key information about the physics of astrophysical objects beyond that given solely in their energy spectra. As indicated in this paper, this information is vital to properly understand the phenomena and processes involved. Given the progress in gamma-ray astronomy, statistical tools can now be applied to study the timing properties of AGN and to characterize their variability in terms of, e.g., flux distributions (PDF) and (temporal) frequency dependence (PSD), along with characteristic timescales and possible QPOs. This positive development is set to strengthen with upcoming instrumental developments and will make it possible to deepen our understanding of the link between accretion dynamics, black hole physics, and jet ejection.
Funding: Funding by a DFG Heisenberg Fellowship RI 1187/6-1 is gratefully acknowledged.
Acknowledgments: Support and hospitality of the Max-Planck-Institut für Kernphysik (MPIK), Heidelberg, is gratefully acknowledged. I would like to thank Daniela Dorner and Thomas Bretz for organizing an inspiring conference, and Nachiketa Chakraborty for helpful comments on the manuscript. I thank S. Sahayanathan and R. Khatoon as well as E. Sobacchi for their permission to use Fig. 7 and 10, respectively.