Physical Sciences and Mathematics Commons^™

The Spectro-Temporal Relationships Of Repeating Fast Radio Bursts, Mohammed Afif Chamma

Electronic Thesis and Dissertation Repository

Fast radio bursts (FRBs) are short and extremely energetic bursts of radiation detected from galaxies across the universe that occur thousands of times a day. Despite advances in instrumentation, it is difficult to explain the enormous implied energy reservoirs of FRBs, their emission mechanism and the existence of repeating and periodic sources. This thesis explores the spectro-temporal properties of repeating FRBs and details the discovery of several new relationships between them, providing valuable information on the nature of FRBs. By measuring the spectro-temporal properties of a sample of bursts from the repeating source FRB20121102A I show that the magnitude of …

The Role Of Nonideal Magnetohydrodynamic Effects, Gravitational Instability, And Episodic Accretion In Star-Formation, Indrani Das

Electronic Thesis and Dissertation Repository

My dissertation focuses on the effect of magnetic fields on disk and core evolution during star-formation. We investigate the fragmentation scales of gravitational instability of a rotationally-supported self-gravitating protostellar disk using linear perturbation analysis in the presence of two nonideal magnetohydrodynamic (MHD) effects: Ohmic dissipation and ambipolar diffusion. Our results show that molecular clouds exhibit a preferred lengthscale for collapse that depends on mass-to-flux ratio, magnetic diffusivities, and the Toomre-Q parameter. In addition, the influence of the magnetic field on the preferred mass for collapse leads to a modified threshold for the fragmentation mass, as opposed to a Jeans mass, …

Probing The Inner Structure Of Active Galactic Nuclei Through Reverberation Mapping, Viraja Chandrashekhar Khatu

Electronic Thesis and Dissertation Repository

In the centres of massive galaxies, active galactic nuclei (AGN) are supermassive black holes, surrounded by an accretion disk of ionized gas, that release tremendous energy in the form of electromagnetic radiation. Because AGN are unresolved through telescopes, we employ reverberation mapping (RM) to study their structure. RM capitalizes on the fact that AGN are variable – the continuum emission from the accretion disk varies, and surrounding gas (in the broad-line region, BLR) responds to those variations with a positive time lag. RM translates the measured time lag into a size of the BLR. Combined with gas velocities (measured from …

The Dynamical Evolution Of Classical Be Stars, Keegan Marr

Electronic Thesis and Dissertation Repository

This thesis focuses on the evolution of the disks of two classical B-emission (Be) stars, 66 Ophiuchi and Pleione, and on the thermal structure for disks tilted out of the star's equatorial plane.

We used a hydrodynamic code to model the disk of the Be star 66 Ophiuchi. Observations from 1957 to 2020 were compiled to follow the growth and subsequent dissipation of the disk. Our models are constrained by new and archival photometry, spectroscopy and polarization observations. Using Markov chain Monte Carlo methods, we confirm that 66 Oph is a B2Ve star. We constrain the density profile of the …