LNRFvelocity humpinduced oscillations of a Keplerian disc orbiting nearextreme Kerr black hole: a possible explanation of highfrequency QPOs in GRS 1915+105
Abstract
Context: At least four highfrequency quasiperiodic oscillations (QPOs) at frequencies 41 Hz, 67 Hz, 113 Hz, and 167 Hz were reported in a binary system GRS 1915+105 hosting nearextreme 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 nonrotating framesLNRF) in discs orbiting nearextreme 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 nonlinear 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 ν_{h} = 41 Hz, ν_{r} = 67 Hz, ν_h+ν_{r} = 108 Hz, and ν_vν_{r} = 170 Hz corresponding quite well to the observed ones.
Conclusions: For blackhole parameters being in good agreement with those given observationally, the forced resonant phenomena in nonlinear oscillations, excited by the “humpinduced” oscillations in a Keplerian disc, can explain highfrequency QPOs in nearextreme Kerr blackhole binary system GRS 1915+105 within the range of observational errors.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 August 2007
 DOI:
 10.1051/00046361:20077051
 arXiv:
 arXiv:0704.1252
 Bibcode:
 2007A&A...470..401S
 Keywords:

 accretion;
 accretion disks;
 black hole physics;
 Astrophysics
 EPrint:
 4 pages, 2 figures, accepted for publication in Astronomy and Astrophysics, added references, corrected typos