Publication date: Dec 2014
Abstract:
We have previously applied several models of high-frequency quasi-
periodic oscillations (HF QPOs) to estimate the spin of the central Kerr
black hole in the 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 a super-spinning object (or a naked
singularity) with the external space-time described by Kerr geometry
with a dimensionless spin parameter a ≡ cJ/GM2> 1. We
calculate the relevant spin intervals for a subset of HF QPO models
considered in the previous study. Our analysis indicates that for all
but one of the considered models there exists at least one interval of
a> 1 that is compatible with constraints given by the ranges of the
central compact object mass independently estimated for the three
sources. For most of the models, the inferred values of a are several
times higher than the extreme Kerr black hole value a = 1. These values
may be too high since the spin of superspinars is often assumed to
rapidly decrease due to accretion when a ≫ 1. In this context, we
conclude that only the epicyclic and the Keplerian resonance model
provides estimates that are compatible with the expectation of just a
small deviation from a = 1.
Authors:
Kotrlová, Andrea; Török, Gabriel; Šrámková, Eva; Stuchlík, Zdeněk;