Understanding X-ray Timing and Radio Observations

Time-dependent x-ray and radio observations of accreting sources give considerable insight into how jets might be produced, both in low-luminosity and high-luminosity situations. I discuss recent observations of binary x-ray sources and AGN that may have a direct bearing on jet production, and I review the theoretical efforts that have been made to understand them. While it is certainly true that jet production can be understood only with a good accretion model, I also argue that accretion onto compact objects cannot be understood without fully taking into account the production of a jet. Jets are probably a fundamental aspect of some accretion modes. In the quest for an integrated model for accretion and jet production I introduce a new accretion concept, the magneticallydominated accretion flow or MDAF, as an altemative to current models for the lowhard state of accreting black holes (and the island state for atoll sources). Although much quantitative work needs to be performed before the concept can evolve into a true model, MDAFs have a number of phenomenological advantages. In addition to providing explanations for several X-ray timing and radio properties of accreting sources, the MDAF suggests a model for the infrared flares in the Galactic center.