Claudio Germana

INAF – Padova Astronomical Observatory

torek, 12. 5. 2009, ob 15h v F6

Low Mass X-ray binaries with either a black hole or a neutron star show power spectra characterized by several enhanced fractions of power at given frequencies, such as Quasi Periodic Oscillations (QPOs). Twin peak high frequency QPOs are typical of Keplerian time-scales a few gravitational radii away from the compact object, hence QPOs may carry fingerprints of General Relativity in the strong field limit.

Most of the proposed models in the past ten years deal with matter or biting the compact object. However the modelling still suffers in explaining many features such as coherence and rms values of the peaks, their frequencies, the observed power law in the power spectra and the emission mechanism which should account for hard X-ray photons.

Recent studies about tidal interaction of small satellites with a compact object have been proposed to explain the NIR-X rayflaring activity observed in the super massive black hole at galactic center. Simulations have shown that small satellites (e.g. asteroids or comets) on highly eccentric orbits can be brought down to the black hole by tidal evolution. Once close to thehole, say within 10 r_g , tides are so strong that small satellites are highly disrupted and can release an energy as high as a few percent of their rest mass.

I will give a general reviewof the QPOs phenomenon in Low Mass X-ray binaries and I will also discuss both preliminary results in modelling this phenomenon with tidal interaction and still open issues.