43 research outputs found
Confronting the models of 3:2 quasiperiodic oscillations with the rapid spin of the microquasar GRS 1915+105
Spectral fitting of the spin a in the microquasar GRS 1915+105 estimate
values higher than a=0.98. However, there are certain doubts about this
(nearly) extremal number. Confirming a high value of a>0.9 would have
significant concequences for the theory of high-frequency quasiperiodic
oscillations (HF QPOs). Here we discuss its possible implications assuming
several commonly used orbital models of 3:2 HF QPOs. We show that the estimate
of a>0.9 is almost inconsistent with two hot-spot (relativistic precession and
tidal disruption) models and the warped disc resonance model. In contrast, we
demonstrate that the epicyclic resonance and discoseismic models assuming the
c- and g- modes are favoured. We extend our discussion to another two
microquasars that display the 3:2 HF QPOs. The frequencies of these QPOs scale
roughly inversely to the microquasar masses, and the differences in the
individual spins, such as a=0.9 compared to a=0.7, represent a generic problem
for most of the discussed geodesic 3:2 QPO models. To explain the observations
of all the three microquasars by one unique mechanism, the models would have to
accommodate very large non-geodesic corrections.Comment: 7 pages, 3 figures, 2 tables; v2: corrections in the introduction,
language corrections (Astronomy & Astrophysics proof-readed version
A non-linear resonance model for the black hole and neutron star QPOs: theory supported by observations
Kilohertz Quasi-Periodic Oscillations (QPOs) have been detected in many
accreting X-ray binaries. It has been suggested that the highest QPO
frequencies observed in the modulation of the X-ray flux reflect a non-linear
resonance between two modes of accreting disk oscillation. This hypothesis
implies certain very general predictions, several of which have been borne out
by observations. Some of these follow from properties of non-linear
oscillators, while the others are specific to oscillations of fluid in strong
gravity. A 3:2 resonant ratio of frequencies can be clearly recognized in the
black-hole as well as in the neutron-star QPO data.Comment: 8 pages, 8 figures, to appear in Proceedings of the Albert Einstein
Century International Conferenc