Investigating Nonlinear Variability of Accretion Disks Around Compact Objects PDF Download

Author: Rebecca A. Phillipson
Publisher:
ISBN:
Category : Accretion (Astrophysics)
Languages : en
Pages : 0

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Book Description
Accreting compact object systems such as X-ray binaries (XRBs; neutron stars and black holes up to tens of solar masses) and active galactic nuclei (AGN; supermassive black holes up to 1e9 solar masses) exhibit variability in their luminosity on many timescales ranging from milliseconds to hundreds of days. Current studies on accretion disks seek to determine how the changes in black hole mass, the rate at which mass accretes onto the central black hole, and the internal and external disk environment affect the observed variability in various bandwidths of light. The fundamental structure of the accretion flow process itself, how it changes and results in the observed variability is not well known. This thesis employs novel methods from nonlinear dynamics to connect the ubiquitously complex variability of XRBs and AGN to the accretion properties and emission and probe commonalities across decades of mass. The methodologies used surpass the capabilities of traditional time series analysis techniques commonly used in astrophysics, such as the power density spectrum and other second order measures of variability, to probe the underlying dynamics. We study the longest light curves to date of XRBs by combining data from multiple all-sky monitors in the 2-20 keV bandpass; the most well-sampled and high precision optical light curves of AGN from the Kepler satellite; and the largest samples to date of long-term monitoring in the hard X-ray of AGN with the Swift/BAT telescope. We find evidence for chaos in a neutron star XRB connected to its superorbital period of 120 days and possibly related to a precession in the accretion disk. We similarly find higher levels of determinism correlate with specific spectral states of XRBs. Among AGN, we find that Type 1 AGN are more likely to exhibit nonlinear behavior than Type 2, obscured AGN are more likely to exhibit stochastic behavior than unobscured AGN, and radio loud sources are more deterministic than radio quiet, with a possible anti-correlation between increased luminosity and nonlinearity. Overall, we hypothesize that specific configurations of the accretion flow onto a compact object result in specific modulations of the emission that can be characterized as deterministic (e.g., possibly related to the presence of a jet-like process), nonlinear (e.g., due to a modulating warp or precession in the accretion disk), or stochastic (e.g., possibly related to the presence of strong outflows or hard X-ray coronal component).