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arXiv · 1406.0871

A Fourier Transformed Bremsstrahlung Flash Model for the Production of X-Ray Time Lags in Accreting Black Hole Sources

John J. Kroon·Peter A. Becker
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Abstract

Accreting black hole sources show a wide variety of rapid time variability, including the manifestation of time lags during X-ray transients, in which a delay (phase shift) is observed between the Fourier components of the hard and soft spectra. Despite a large body of observational evidence for time lags, no fundamental physical explanation for the origin of this phenomenon has been presented. We develop a new theoretical model for the production of X-ray time lags based on an exact analytical solution for the Fourier transform describing the diffusion and Comptonization of seed photons propagating through a spherical corona. The resulting Green's function can be convolved with any source distribution to compute the associated Fourier transform and time lags, hence allowing us to explore a wide variety of injection scenarios. We show that thermal Comptonization is able to self-consistently explain both the X-ray time lags and the steady-state (quiescent) X-ray spectrum observed in the low-hard state of Cyg X-1. The reprocessing of bremsstrahlung seed photons produces X-ray time lags that diminish with increasing Fourier frequency, in agreement with the observations for a wide range of sources.

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John J. Kroon, Peter A. Becker. 2014-06-03. A Fourier Transformed Bremsstrahlung Flash Model for the Production of X-Ray Time Lags in Accreting Black Hole Sources. https://doi.org/10.1088/2041-8205%2F785%2F2%2Fl34

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