The Jet Paradigm

The discovery of the ?rst case of superluminal radio jets in our galaxy in 1994 from the bright and peculiar X-ray source GRS 1915+105 has opened the way to a major shift in the direction of studies of stellar-mass accreting binaries. The past decade has seen an impressive increase in multi-wavelength studies. It is now known that all black hole binaries in our galaxy are radio sources and most likely their radio emission originates from a powerful jet. In addition to the spectacular events related to the ejection of superluminal jets, steady jets are known from many systems. Compared with their supermassive cousins, the nuclei of active galaxies, stellar-mass X-ray binaries have the advantage of varying on time scales accessible within a human life (sometimes even much shorter than a second). This has led to the ?rst detailed studies of the relation between accretion and ejection. It is even possible that, excluding their “soft” periods, the majority of the power in gal- tic sources lies in the jets and not in the accretion ?ows. This means that until a few years ago we were struggling with a physical problem, accretion onto compact objects, without considering one of the most important components of the system. Models that associate part of the high-energy emission and even the fast aperiodic variability to the jet itself are now being proposed and jets can no longer be ignored.

These Lecture Notes focus on the physics of relativistic jet sources in the universe, from galactic microquasars to active galactic nuclei (AGN). The early 21^st century is an epoch in which a large number of high-energy astronomical missions are underway (RossiXTE, Chandra, XMM-Newton, INTEGRAL, Swift, Suzaku). The wealth of X-ray and gamma-ray data, coupled with ground-based observations in the optical/IR/radio bands, provides an increasing amount of information on microquasars, allowing the investigation of the physical processes for the formation and the evolution of relativistic jets, as well as their relation to the accretion process. The information obtained from galactic relativistic jet systems is particularly important in that it can be compared with that from active galactic nuclei. The comparative study of these two classes of objects allows us to overcome their separate intrinsic limitations and is the only way to arrive at a comprehensive understanding of the accretion/ejection phenomenon.

This book covers the topic of accretion/ejection in relativistic jet sources with a broad approach, from microquasars to AGN, discussing both observational and theoretical aspects. The aim is to present a broad view of the field and the current standpoint now that the first comparative studies have opened the way to a global study at a mass scale. Written in a pedagogical lecture notes style, the book benefits students and newcomers to jet astrophysics as well as lecturers and researchers.