Quasi-periodic oscillations (QPOs) observed in the power spectrum of black
    holes are unique observational probes to the background spacetime since they
    can be directly related to the timescales associated with the motion of matter
    orbiting in the vicinity of the black hole horizon. In this regard, the high
    frequency QPOs (HFQPOs) are particularly interesting as they occur in
    commensurable pairs, the most common ratio being the 3:2 twin peak QPOs. The
    theoretical models which aim to explain these QPOs express the observed
    frequencies in terms of the epicyclic motion of test particles in a given
    background spacetime. In this work we study the signatures of Bardeen spacetime
    from the observed QPOs in the black hole power spectrum. Bardeen black holes
    are rotating, regular black holes with a magnetic monopole charge. Such regular
    backgrounds are theoretically interesting as they can potentially evade the
    curvature singularity, otherwise unavoidable in general relativistic black
    holes. We perform a chi-square analysis by comparing the available observations
    of the quasi-periodic oscillations from black hole sources with the relevant
    theoretical models and note that the Kerr black holes in general relativity are
    observationally more favored compared to black holes with a monopole charge.
    Our analysis reveals that black holes with very high monopole charge are
    disfavored from QPO related observations.

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