Publication date: Dec 2005
Abstract:
It is highly probable that a non-linear resonance between some modes of
oscillations in the accretion discs around black holes and neutron stars
can play a crucial role in exciting detectable modulations of the X-ray
flux. Detailed studies of the resonance models revealed that several of
such non-linear resonances are possible in nearly Keplerian discs in
strong gravity. Moreover, this idea seems to be strongly supported by
observations – in all four microquasars showing twin peak QPOs
(quasiperiodic oscillations), the ratio of frequency peaks is 3:2. In
principle, using known frequencies of the twin peaks and the known mass
of the central black hole, the black-hole spin can be determined. This
was already done for the presently known sources and few miscellaneous
resonance models. Details of excitation mechanisms of eventual
resonances are still not fully explained, nevertheless one can imagine
that not only one resonance could be excited in the accretion disc.
Thus, if two such different resonances are present (by an accident or
because of some causal connection), the black hole spin can be precisely
determined independently of the knowledge of the black hole mass, for
some specific cases discussed here.
Authors:
Stuchlík, Zdeněk; Török, Gabriel;