Type of Document	Dissertation
Author	Bradley, Charles
Author's Email Address	cbrad11@lsu.edu
URN	etd-07072009-123333
Title	States and State Transitions in Low Mass X-Ray Binaries
Degree	Doctor of Philosophy (Ph.D.)
Department	Physics & Astronomy
Advisory Committee	Advisor Name Title Hynes, Robert Committee Chair Frank, Juhan Committee Member Matthews, James Committee Member Tohline, Joel Committee Member Sengupta, Ambar Dean's Representative
Keywords	mass transfer black holes accretion disks binary stars
Date of Defense	2009-06-09
Availability	unrestricted
Abstract We investigate the model of a disk/coronal accretion flow into a black hole. We build a numerical code to ascertain whether the inner regions of an accretion disk in X-ray binaries can transform from a cool standard disk to an advection-dominated flow through the known properties of Coulomb interaction in a two-temperature plasma, taking into account viscous heating, standard radiation processes, and thermal conduction. A hot, diffuse corona covering the whole disk is powered by accretion, but it exchanges energy with the underlying cool disk through radiative interactions and conduction. If the accretion rate is low enough, at some intermediate radius the corona begins to evaporate the cool disk away, leaving an advective coronal flow to continue towards the hole as consistent with X-ray observations that I have studied using XMM-Newton and Chandra. We show that if the accretion rate increases sufficiently, complete evaporation does not occur and the cool inner disk remains, proceeding inward to the innermost stable orbit. During spectral transitions an intermediate state has been observed whose nature is unclear, but which shows the presence of cold matter near an X-ray emitting source, along with an additional component that could come from an advective coronal flow. We build a steady-state model that includes these effects and mass exchange between the two flows through evaporation and recondensation during the soft/hard transition and create a "hysteresis" similar to that observed, along with representative spectra for each X-ray state.
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