Beat-Frequency Models of Kilohertz QPOs

Abstract

Kilohertz QPO sources are reasonably well-characterized observationally, but many questions remain about the theoretical framework for these sources and the consequent implications of the observations for disk physics, strong gravity, and dense matter. We contrast the predictions and implications of the most extensively studied class of kilohertz QPO models, the beat-frequency models, with those of alternative classes of models. We also discuss the expected impact of new observations of these sources with satellites such as Chandra, XMM, and Constellation-X.Comment: 10 pages, invited paper at Bologna X-ray Astronomy 1999. To appear in Astrophysical Letters and Communication