Publication date: Aug 2007
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.
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.
Stuchlík, Z.; Slaný, P.; Török, G.;