Superspinning compact objects and models of highfrequency quasiperiodic oscillations observed in Galactic microquasars
Abstract
We have previously applied several models of highfrequency quasiperiodic oscillations (HF QPOs) to estimate the spin of the central Kerr black hole in the three Galactic microquasars, GRS 1915+105, GRO J165540, and XTE J1550564. Here we explore the alternative possibility that the central compact body is a superspinning object (or a naked singularity) with the external spacetime described by Kerr geometry with a dimensionless spin parameter a ≡ cJ/GM^{2}> 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.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 December 2014
 DOI:
 10.1051/00046361/201424407
 arXiv:
 arXiv:1410.6129
 Bibcode:
 2014A&A...572A..79K
 Keywords:

 Xrays: binaries;
 black hole physics;
 accretion;
 accretion disks;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 6 pages, 4 figures, accepted by A&