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We have previously applied several models of high-frequency quasi-periodicoscillations (HF QPOs) to estimate the spin of the central Kerr black hole inthe three Galactic microquasars, GRS 1915+105, GRO J1655-40, and XTE J1550-564.Here we explore the alternative possibility that the central compact body is asuper-spinning object (or a naked singularity) with the external space-timedescribed by Kerr geometry with a dimensionless spin parameter a = cJ/GM2 >1.We calculate the relevant spin intervals for a subset of HF QPO modelsconsidered in the previous study. Our analysis indicates that for all but oneof the considered models there exists at least one interval of a > 1 that iscompatible with constraints given by the ranges of the central compact objectmass independently estimated for the three sources. For most of the models, theinferred values of a are several times higher than the extreme Kerr black holevalue a = 1. These values may be too high since the spin of superspinars isoften assumed to rapidly decrease due to accretion when a >> 1. In thiscontext, we conclude that only the epicyclic and the Keplerian resonance modelprovides estimates that are compatible with the expectation of just a smalldeviation from a = 1.

Super-spinning compact objects and models of high-frequency quasi-periodic oscillations observed in Galactic microquasars