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Session 36 - New Insights on X-ray Binaries - I.
Oral session, Wednesday, June 11
North Main Hall C/D,
Recent results obtained with the Rossi X-ray Timing Explorer on X-ray binaries are reviewed, with particular emphasis on the newly found kilohertz quasi-periodic oscillations, now known to occur in more than a dozen neutron-star systems. kHz QPO are the fastest oscillations known in X-ray binaries (they are one of the fastest phenomena in the sky) and it is likely that they provide a probe to deep down into the gravitational well of the compact object. For this reason they may be able to provide us with new information about the fundamental properties of neutron stars and help testing general relativity in the strong-field regime. If, for example, their frequencies can be identified with the Keplerian frequencies of matter in orbit around a 1.4 Solar mass neutron star, then the radius of the star would have to be less than 15 km, which directly constrains the equation of state of bulk nuclear-density matter, and for an only slightly tighter orbit or slightly more massive neutron star the orbital radius would equal the Schwarzschild- geometry general-relativistic marginally stable orbit (12.5 km for a 1.4 Solar mass object). In black hole candidate systems, QPO phenomena have been found (which may or may not be related) that have been interpreted in terms of general-relativistic orbital instabilities as well. I review the, at least in neutron star systems, relatively simple and highly suggestive phenomenology as it has emerged from the data up to now, and discuss some of the general ideas and models that have been proposed over the last few months.
