Publication date: n/a 2006
Abstract:
Kilohertz Quasi-Periodic Oscillations (QPOs) have been detected in many
accreting X-ray bi- naries. It has been suggested that the kHz QPO
frequencies observed in the modulation of the X-ray flux reflect a
non-linear resonance between two modes of accreting disk oscillations. A
3:2 resonant ratio of frequencies has been clearly recognized in the
black-hole QPO data supporting the non-linear resonance hypothesis. It
is often discussed whether the same 3:2 ratio appears in case of the
neutron star QPOs as well. For an individual neutron star source, the
relation between the observed lower and upper (νL and νU ) kHz QPO
frequency is well approximated by a linear relation with the slope A and
the shift B, i.e., νU = AνL + B. It was recognized only recently
that for a group of twelve neutron star sources the value of the
individual coefficients A, B is anticorre- lated, obeying the condition
A = 3/2 – 0.0016B. It was also shown that such an anticorrelation is
predicted by the theory of weakly coupled nonlinear oscillators, and one
can argue that it indeed pose the evidence for a 3:2 resonant ratio.
Here, stressing the latest progress, we discuss some of the links
between the QPO observation and the resonance model, and summarize the
appropriate references. Except the slightly updated list of references,
the content of next four pages fully correspond to the A0 poster we
exhibited at the VI Microquasar Workshop. The poster itself is available
at the http://www.physics.cz/research (section Conferences).
Authors:
Torok, Gabriel; Abramowicz, M. A.; Kluzniak, W.; Stuchlik, Z.; Rámková, E.;