Publication date: Aug 2007
Abstract:
Context: At least four high-frequency quasiperiodic oscillations (QPOs)
at frequencies 41 Hz, 67 Hz, 113 Hz, and 167 Hz were reported in a
binary system GRS 1915+105 hosting near-extreme Kerr black hole with a
dimensionless spin a > 0.98. Aims: We attempt to explain all
four observed frequencies by an extension of the standard resonant model
of epicyclic oscillations. Methods: We use the idea of
oscillations induced by the hump of the orbital velocity profile
(related to locally non-rotating frames-LNRF) in discs orbiting
near-extreme Kerr black holes, which are characterized by a “humpy
frequency” ν_h, that could excite the radial and vertical
epicyclic oscillations with frequencies ν_r, ν_v. Due to
non-linear resonant phenomena, the combinational frequencies are allowed
as well. Results: Assuming mass M = 14.8 M⊙ and
spin a = 0.9998 for the GRS 1915+105 Kerr black hole, the model predicts
frequencies νh = 41 Hz, νr = 67 Hz,
ν_h+νr = 108 Hz, and ν_v-νr = 170 Hz
corresponding quite well to the observed ones. Conclusions: For
black-hole parameters being in good agreement with those given
observationally, the forced resonant phenomena in non-linear
oscillations, excited by the “hump-induced” oscillations in
a Keplerian disc, can explain high-frequency QPOs in near-extreme Kerr
black-hole binary system GRS 1915+105 within the range of observational
errors.
Authors:
Stuchlík, Z.; Slaný, P.; Török, G.;