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Light Echos in Kerr Geometry: A Source of High Frequency QPOs from Random X-ray BurstsWe propose that high frequency quasi-periodic oscillations (HFQPOs) can be produced from randomly-formed X-ray bursts (flashes) by plasma interior to the ergosphere of a rapidly-rotating black hole. We show by direct computation of their orbits that the photons comprising the observed X-ray light curves, if due to a multitude of such flashes, are affected significantly by the black hole's dragging of inertial frames; the photons of each such burst arrive to an observer at infinity in multiple (double or triple), distinct 'bunches' separated by a roughly constant time lag of t/M approximately equal to 14, regardless of the bursts' azimuthal position. We argue that every other such 'bunch' represents photons that follow trajectories with an additional orbit around the black hole at the photon circular orbit radius (a photon 'echo'). The presence of this constant lag in the response function of the system leads to a QPO feature in its power density spectra, even though the corresponding light curve consists of a totally stochastic signal. This effect is by and large due to the black hole spin and is shown to gradually diminish as the spin parameter a decreases or the radial position of the burst moves outside the static limit surface (ergosphere). Our calculations indicate that for a black hole with Kerr parameter of a/M=0.99 and mass of M=10*Msun the QPO is expected at a frequency of approximately 1.3-1.4 kHz. We discuss the plausibility and observational implications of our model/results as well as its limitations.
Document ID
20080031161
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Fukumura, K.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Kazanas, D.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 24, 2013
Publication Date
January 7, 2008
Subject Category
Astronomy
Meeting Information
Meeting: AAS Meeting
Location: Austin, TX
Country: United States
Start Date: January 7, 2008
End Date: January 11, 2008
Sponsors: American Astronomical Society
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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