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Title:
How to Find if Your Black Hole is Rapidly Rotating: Searching for the Ergosphere with X-ray Timing
Authors:
Fukumura, Keigo; Kazanas, D.
Affiliation:
AA(UMBC/CRESST/NASA), AB(NASA/GSFC)
Publication:
American Astronomical Society, AAS Meeting #214, #304.05; Bulletin of the American Astronomical Society, Vol. 41, p.721
Publication Date:
05/2009
Origin:
AAS
Bibliographic Code:
2009AAS...21430405F

Abstract

It has been suggested mainly from X-ray spectroscopic observations (e.g. thermal disk emission and Fe emission line) that at least a number of active galactic nuclei (AGNs) and Galactic black hole (BH) systems host rapidly-rotating (Kerr) BHs. In this presentation we show that random X-ray flares in the ergosphere around a fast-rotating BH can in principle produce a coherent signal due to its inevitable frame-dragging (light echo model) regardless of their exact positions. We discuss autocorrelation and power spectra based on our model light curve and show that this coherence leads to a high frequency quasi-periodic oscillation (QPO) that only depends on the BH mass (not flux or spectral state); e.g. kHz for stellar-mass BHs while mHz for AGNs. The QPOs predicted in this model therefore would be present, if exists, among the (Poisson) white noise frequency band. While with current X-ray detectors this type of QPO could be present well below the noise, future missions like IXO and Astro-H should be capable of reducing the noise (or increase statistics) to a sufficient level where the QPOs would actually stand out. This QPO should be viewed as a new class of QPO inherent to curved spacetime geometry of a fast rotating of BHs (frame-dragging) described by Einstein's general relativity.
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