2016A&A...586A.130S

Frequencies of the three quasi-periodic oscillation (QPO) modes observed simultaneously in the accreting black hole GRO J1655-40 are compared with the predictions of models. Models in which all three QPO signals are produced at the same radius are considered: these include different versions of relativistic precession, epicyclic resonance, tidal disruption, and warped disc models. Models that were originally proposed to interpret only the twin high-frequency QPOs are generalized here to interpret also the low-frequency QPO in terms of relativistic nodal precession. Inferred values of the black hole mass and spin from each QPO model are compared with the mass measured from optical observations and the spin inferred from X-ray spectroscopy techniques. We find that along with the relativistic precession model predicting M=(5.3±0.1)M_☉, a=0.286±0.004, the so-called total precession model (M=(5.5±0.1)M_☉, a=0.276±0.003), and the resonance epicyclic model with beat frequency (M=(5.1±0.1) M_☉, a=0.274±0.003) also satisfy the optical mass test.