Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item The interplay between the central engine and the circumnuclear environment in Compton-thin AGN(Montana State University - Bozeman, College of Letters & Science, 2022) Chalise, Sulov; Chairperson, Graduate Committee: Anne Lohfink; This is a manuscript style paper that includes co-authored chapters.All massive galaxies harbor a supermassive black hole (SMBH) at their galactic center. If these SMBH are actively feeding then they are called Active galactic nuclei (AGN). Their accretion system contains a corona, an accretion disk and an axisymmetric dusty torus. The torus can be connected physically and dynamically to the circumnuclear disk of the galaxy which acts as a molecular gas reservoir for material to be accreted onto the SMBH. Further, AGN can emit radiation from radio up to the gamma rays. The AGN accretion disk emits photons mostly in the optical/UV band which are Compton up-scattered in the corona to generate X-rays. If present, a jet can produce additional high-energy and Synchrotron emission. In some AGN, a huge amount of material can be stripped away from the accretion disk creating an outowing wind. These --radiation pressure, jet, wind etc.--inject energy back into the host galaxy, regulating the SMBH growth. There exist a complex interplay between the AGN feeding and feedback. Understanding this interaction between the central engine and its circumnuclear environment is vital in context of galaxy evolution. My work aims to study this interaction in low to moderately obscured (or Compton-thin) AGN using their broadband multi-epoch X-ray spectra plus other emission bands whenever appropriate. From the spectral analysis of broad-line radio galaxy 3C 109, I was able to constrain its high-energy cutoff for the first time. In another Seyfert galaxy Mrk 926, I was able to explore the origin of its soft excess, and found that a warm coronal origin was slightly preferred. Finally, I performed a joint multi-wavelength analysis with a physical torus model of a sample of Polar-scattered Seyfert 1 galaxies. I utilized their multi-epoch broadband X-ray spectra along with their infrared spectral/photometric data, and was able to constrain their torus properties. Despite being a sample of similar moderately-inclined Compton-thin AGN, I found a complex and varied distribution of gas and dust in their torus.Item A deeper look into X-ray-selected AGN candidates in dwarf galaxies with Chandra(Montana State University - Bozeman, College of Letters & Science, 2023) Sanchez, Adonis Arismendy; Chairperson, Graduate Committee: Amy E. Reines; This is a manuscript style paper that includes co-authored chapters.The ability to accurately discern active massive black holes (BHs) in local dwarf galaxies is paramount to understanding the origins and processes of "seed" BHs in the early universe. We present Chandra X-ray Observatory observations of a sample of three dwarf galaxies (M* < or = 3 x 109 M circled dot, z < or = 0.15) pre-selected by Latimer et al. (2021a) as candidates for hosting active galactic nuclei (AGN). The galaxies were selected from the NASA-Sloan Atlas (NSA) with spatially coincident X-ray detections in the eROSITA Final Equatorial Depth Survey (eFEDS). Our new Chandra data reveal X-ray point sources in two of the three galaxies with luminosities of log(L 2-10keV/[erg s -1]) = 39.1 and 40.4. In the target galaxy with the nondetection, we calculate an upper limit on the luminosity for a potential source. We observed notably higher fluxes and luminosities from the two detected X-ray sources compared to their original eFEDS observations, pointing to possible X-ray variability on the scale of a few years. We plot and fit the spectra of the X-ray sources with a power-law model, finding the likely presence of intrinsic absorption. The X-ray luminosities are above that expected from XRBs, but we cannot definitively rule out stellar-mass compact objects with the data on hand. Assuming the X-ray sources are accreting massive BHs with masses that scale with the stellar mass of the host galaxies, the Eddington ratios are on the order of a few x 10 -3.Item X-ray analysis and modeling of NGC 3227(Montana State University - Bozeman, College of Letters & Science, 2022) Newman, Jared James; Chairperson, Graduate Committee: Yves U. Idzerda and Sachiko Tsuruta (co-chair)The 1.5 Seyfert galaxy NGC 3227 has been observed by several X-ray missions. We carried out combined analysis of the data from a total of twenty one observations. Six of the observations were preformed by Suzaku, eight by XMM-Newton, and seven by NuStar. A unified model was constructed which is consistent with all twenty one of the observations by the three satellites with large intensity and spectral changes. The model consists of a hard power law which is interpreted as the Comptonized emission from the corona above an accretion disk. In the high flux states an additional soft excess component dominates, which is consistent with a model with either a steeper power law or a warm Comptonization component. These emissions from the central engine are absorbed by multiple distinct absorbers at various ionization levels. A reflection component and several emission lines are also present. This is the most robust model of this source to date.Item Collision of photons by the use of x-rays(Montana State University - Bozeman, College of Letters & Science, 1940) Wiegand, Roy V.Item Combining hydrodynamic modeling with nonthermal test particle tracking to improve flare simulations(Montana State University - Bozeman, College of Letters & Science, 2009) Winter, Henry deGraffenried, III; Chairperson, Graduate Committee: Petrus MartensSolar flares remain a subject of intense study in the solar physics community. These huge releases of energy on the Sun have direct consequences for humans on Earth and in space. The processes that impart tremendous amounts of energy are not well understood. In order to test theoretical models of flare formation and evolution, state of the art, numerical codes must be created that can accurately simulate the wide range of electromagnetic radiation emitted by flares. A direct comparison of simulated radiation to increasingly detailed observations will allow scientists to test the validity of theoretical models. To accomplish this task, numerical codes were developed that can simulate both the thermal and nonthermal components of a flaring plasma, their interactions, and their emissions. The HYLOOP code combines a hydrodynamic equation solver with a nonthermal particle tracking code in order to simulate the thermal and nonthermal aspects of a flare. A solar flare was simulated using this new code with a static atmosphere and with a dynamic atmosphere, to illustrate the importance of considering hydrodynamic effects on nonthermal beam evolution. The importance of density gradients in the evolution of nonthermal electron beams was investigated by studying their effects in isolation. The importance of the initial pitch-angle cosine distribution to flare dynamics was investigated. Emission in XRT filters were calculated and analyzed to see if there were soft X-ray signatures that could give clues to the nonthermal particle distributions. Finally the HXR source motions that appeared in the simulations were compared to real observations of this phenomena.Item X-ray characterization of buried layers and interfaces in EuO based spin-filter tunnel junctions(Montana State University - Bozeman, College of Letters & Science, 2008) Negusse, Ezana; Chairperson, Graduate Committee: Yves U. Idzerda; V. Hugo Schmidt (co-chair)Spin filtering tunnel junctions provide a convenient method for controlling and manipulating the spin of electrons in spintronic devices. In a tunnel junction, the tunneling current depends exponentially on the thickness of the tunneling barrier. Ultrathin (~20 angstroms) barriers are highly desirable because they lower the junction resistance. In addition to the barrier thickness, the spin filtering efficiency of the junction depends on the tunneling barrier's magnetic properties and the nature of the barrier-electrode interfaces. EuO's high TC (69 K) and large exchange splitting (2 ΔE = 0.54 eV) in the conduction band make it a material of choice for achieving a spin-polarized tunneling current. We examined the properties of ultrathin EuO films of different thicknesses with different electrodes. The chemical and magnetic characterization of buried layers and buried interfaces was done using interface sensitive x-ray techniques with element specificity and magnetic contrast. Of the many materials studied, we found that yttrium overlayers are the best electrodes to protect the EuO barrier and prevent formation of Eu2O3, a stable nonmagnetic oxide, at the top (EuO-electrode) interface. We examined the electrode-EuO interfaces of EuO films with Cu bottom electrode deposited on Cr/Cu buffer layer. We found that the roughness of the top and bottom interfaces (above and below the EuO layer) is random and nonconformal in nature. EuO films grown on Cr/Cu buffer layer have smoother top interfaces compared to those deposited directly on Si substrate or Al bottom electrode. Moreover, compared to the Cr/Cu or Cu/EuO interfaces, the top (EuO-electrode) interface is smoother. Here we present results from chemical and magnetic characterization of ultrathin EuO film and the impact of reduced barrier thickness on the magnetic properties of the ferromagnetic tunneling barrier.Item Temporal and dynamical spectral analysis of select narrow line Seyfert 1 galaxies(Montana State University - Bozeman, College of Letters & Science, 2010) Liebmann, Andrew Cargill; Chairperson, Graduate Committee: Sachiko TsurutaPresented is the detailed analysis of three Narrow Line Seyfert 1 galaxies using the method of dynamical spectral analysis. These are NGC 4051, IRAS F12397+3333 and Mrk 766. The highly variable NGC 4051 exhibits some dramatic changes over the course of two observations. These dramatic changes are attributed to a variable emission region being partially covered by a fixed, thick absorbing cloud. A unique time region was found where the emission region becomes smaller than the absorbing cloud. Source enters a true minimal phase and appears quite stable, appearing to "turn off." When in its lowest flux states NGC 4051 has a thermal plasma feature suggesting starburst activity in the nucleus. The possibility of starburst activity proves an important link in the understanding of the evolution of Active Galactic Nuclei. IRAS F12397+3333, a little studied source, was found to possess a complex, dusty, warm absorber spectrum of helium- and hydrogen-like carbon, nitrogen, oxygen, neon and several ionic species of iron. This is similar to the spectrum of IRAS 13349+2348. A two-phase gas was used to model this spectrum. The location of the gas is consistent with being located in the narrow line region. Two types of variability were found in the rapidly varying Mrk 766. The longterm variability and its associated spectral flattening seen in two observations are caused by a thick partially covering cloud and variable emission region. However the average spectral behavior shows partial covering of a thinner cloud. The result is a "lumpy cloud." When the source is dim a thicker portion of the clouds covers it, but as the source brightens and enlarges the thinner portion plays a more dominant role in the covering. The short, rapid variability is caused by the combination of a highly variable power law component and a stable reflected component, referred to here as ionized relativistic reflection. Finally, some unique flares were discovered. Unlike the other flares seen in the lightcurves, these occur only in the 0.3-2.0 keV band. They are attributed as a 'hot spot' on the accretion disk.