Abstracts Astronomy & Space Science

The Effects of Winds on Accretion Disks and Spectra Of X-Ray Binaries and Active Galactic Nuclei

by Shalini Ganguly

Active galactic nuclei (AGNs) and X-ray binaries (XRBs) contain at their cores supermassive black holes (SMBH), and stellar mass black holes or neutron stars, respectively. These objects bind matter gravitationally, leading to the formation of accretion disks. The accretion of matter leads to efficient conversion of gravitational potential energy into radiation. When the force and/or energy imparted by this radiation on matter exceeds the attractive force due to the local gravitational field, it leads to the launching of matter in the form of outflows or winds. These outflows produce blueshifted (and occasionally redshifted) emission or absorption components in the spectra of these sources. For instance, Seyfert galaxies generally display absorption lines with relatively small blueshifts (∼ 100 –1000 km s−1) in their UV and X-ray spectra, indicating the presence of mass outflows. In some such galaxies, the Xray absorbers (the so-called warm absorbers, WAs) and UV absorbers have very similar velocities which suggests that these absorbers are nearly cospatial. This, in turn, suggests that regions of very different temperatures coexist and that the absorption occurs in a multi-phase outflow.In this dissertation, we study two distinct effects of disk winds/outflows: (a) self-regulating effects on accretion disks, and (b) effects on the background continuum radiation due to absorption. The self-regulating disk-wind feedback process is an example of how disk winds can regulate the time evolution of the entire accretion disk. We develop a one-dimensional radial hydrodynamic code to study the evolution of such a disk. By relaxing the condition of a fixed wind launching radius, we find that an accretion disk is destabilized for much stronger winds than previously predicted for a fixed launching radius model. We then compute thermally-driven outflow models irradiated by an AGN continuum, using the magnetohydrodynamics code ATHENA++. An isobaric perturbation can trigger thermal instability leading to the formation of multi-phase outflows that can have distinguishing effects on the absorption line profiles. To study such effects, we develop and test a pipeline written in Python, which combines results from ATHENA++ and the photoionization calculation code XSTAR. We use this pineline to generate the absorption line profiles based on our outflow solutions. We discuss how absorption line profiles produced by different species could help distinguish smooth outflows from multi-phase ones.