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IAU Symposium 290

FEEDING COMPACT OBJECTS: Accretion on All Scales

20 - 24 August 2012, Beijing, China

IAU General
Assembly 2012 Logo

Scientific rationale:

This decade is seeing an unprecedentedly large number of high-energy space missions covering an energy range from soft X-rays to gamma rays. This, in connection to powerful optical and radio telescopes on the ground, provides the best set of tools to study accreting compact objects. While for a long time the focus has been on high-energy emission from the accretion flow, it is now clear that the accretion process on all scales is intimately connected to the ejection of powerful jets and that these two phenomena must be studied together. For AGN the association with jets was known, but the long time scales involved did not allow a detailed study of the connection between accretion and ejection. In the past two decades, the discovery of jet emission from X-ray binaries has opened the way to the study of these phenomena in real time, down to time scales as short as hours or minutes. This led to an increasing number of multi-wavelength campaigns which, although difficult to set up, yield the necessary broad-band view.

As both the accretion and ejection processes depend on the properties of the system in the close vicinity of the compact object, their properties are expected to be independent of the nature of the system on larger scales. The fundamental properties of accretion are expected to be the same for all these objects, after some basic scaling laws are taken into account. The presence of these scaling laws indicate that it should be possible to identify basic properties that link together systems of widely different mass, from AGN to X-ray binaries to cataclysmic variables.

The so-called fundamental plane of AGN and black-hole binaries, which links the radio and X-ray flux of accreting objects over more than 10 orders of magnitude has provided the first strong link. Neutron-star binaries have been added, although they appear to be under-luminous in radio. Spectral-wise, the use of basic hardness indicators have led to a proposed unified picture that links the ejection of fast relativistic jets to the changes in the properties of the accretion flow, providing the first evidence of a direct real-time connection between accretion and ejection. This picture, originally developed for black-hole binaries, has been extended to neutron-star binaries and AGN, and recently to cataclysmic variables, where only a few observations of this type are available. On the side of variability, the mass scaling properties have been long hidden because of the effects due to changes in mass accretion rate, but they have now been discovered: black-hole binaries and AGN do display properties that can be scaled with mass, while neutron-star binaries present slight differences most likely related to their peculiarities (mass, magnetic field).

The Symposium aims at connecting the lines of research on different classes of objects by bringing together scientists from parallel fields. The main emphasis will be given to common aspects across systems. Different approaches to the measurement of fundamental parameters such as black hole masses and angular momenta will be discussed and compared. These are inevitably linked to accretion models and most likely to the hitherto unknown mechanism for the ejection of relativistic jets, which is ubiquitous and seems to be inhibited only by the presence of a strong ordered magnetic field.

Contact IAU Symposium 290: iaus290@bao.ac.cn