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;