Department of Physics
http://hdl.handle.net/10106/4972
2024-03-29T01:01:50ZCORE-COLLAPSE SUPERNOVAE AND THEIR REMNANTS: CHANDRA STUDY OF SN 1987A AND A MULTI-WAVELENGTH FOLLOW-UP OF SN 2021KRF
http://hdl.handle.net/10106/31772
CORE-COLLAPSE SUPERNOVAE AND THEIR REMNANTS: CHANDRA STUDY OF SN 1987A AND A MULTI-WAVELENGTH FOLLOW-UP OF SN 2021KRF
**Please note that the full text is embargoed until 8/1/2024** ABSTRACT: Understanding how exploding stars impact their surroundings is of fundamental importance to all areas of astrophysics. Young supernovae (SNe) and their remnants open a window into directly studying the composition and distribution of the fresh products of nucleosynthesis. They also are instrumental in probing the ambient circumstellar medium (CSM), revealing the late-stage evolution of massive stars that culminates in a cataclysmic explosion. My thesis is divided into understanding the evolution of two core-collapse SNe: SN 1987A and SN 2021krf.
Supernova (SN) 1987A is the closest observed SN (about 51 kpc) in the last 400 years and offers a unique opportunity to understand the makings of a supernova remnant (SNR) from a core-collapse supernova (CCSN). Based on observations with the Chandra X-ray Observatory, we present the latest spectral and photometric evolution of the X-ray remnant of SN 1987A (SNR 1987A). With high-resolution Chandra HETG spectral modeling, we find an increase in electron temperatures (by about 40 %) and decreasing volume emission measures between 2011 and 2018 which suggest that the shocks moving through the inner ring have started interacting with less dense CSM, probably beyond the inner ring. The soft (0.5-2.0 keV) X-ray light curve shows a linearly declining trend (by about 18 %) between 2016 and 2020 as the blast wave heats the low-density CSM from the red supergiant phase of SN 1987A’s progenitor. The Chandra ACIS X-ray spectra of SNR 1987A since 2018 show the emerging presence of the Fe K line suggesting an increasing contribution from the reverse shocked layers of the SN ejecta. The morphological evolution and changes in the expansion rate of SNR 1987A are also consistent with these physical interpretations.
We also present the near-infrared (NIR) and optical observations of the recent Type Ic supernova (SN Ic) SN 2021krf performed between days 13 and 259 since the explosion with several ground-based telescopes. The NIR spectrum at day 68 exhibits a rising K-band continuum flux density longward of about 2.0 microns indicating the presence of dust, likely formed in the SN ejecta. At late times (70–300 days), we find that the optical light curves of SN 2021krf decline substantially more slowly than that expected from 56-Co radioactive decay. We reproduced the entire bolometric light curve with a combination of radioactive decay and an additional powering source in the form of a central engine of a millisecond pulsar with a magnetic field of typical radio pulsars.
2023-08-08T00:00:00ZRelation Between Solitary Wave Occurrence and Solar Wind Parameters During the Kelvin-Helmholtz Instability
http://hdl.handle.net/10106/31718
Relation Between Solitary Wave Occurrence and Solar Wind Parameters During the Kelvin-Helmholtz Instability
The Kelvin-Helmholtz instability (KHI) is an important mechanism whereby the solar wind transports energy and momentum into the magnetosphere. One unresolved topic is the role of kinetic phenomena and turbulence in mediating this energy transport. Previous studies hypothesized that the prevalence of electrostatic solitary waves, an artifact of kinetic turbulence, decreased along the flanks as the instability grew. These previous studies had been conducted using 3 KHI events. For this study, we test the hypothesis and further investigate how these solitary waves affect the local plasma with an expanded list of 15 KHI events. A combination of solar wind data from OMNI and in-situ plasma measurements from the NASA Magnetospheric Multiscale (MMS) mission was taken for the duration of these events. Analysis of the findings show that solitary wave occurrence seems to coincide with ion temperature isotropy and electron temperature anisotropy biased to the direction parallel to the magnetic field. It was further observed that solitary wave occurrence was highly negatively correlated with the position of the KHI event along the magnetospheric flank, supporting the previous hypothesis. Additional correlations to solar wind velocity and pressure were also found.
2023-08-07T00:00:00ZSensitivity Study for Low Mass Dark Matter Search at DUNE
http://hdl.handle.net/10106/31702
Sensitivity Study for Low Mass Dark Matter Search at DUNE
Many anomalies in the predictions of mass and gravity at the galactic scale have been attributed to an elusive form of matter we refer to as dark matter. The excessive rotational velocity of galaxies and gravitational lensing observed in the cosmos have not found any explanation within the standard model of physics. However, dark matter itself remains undetected as it seems to only interact with gravity. If it does interact with other forces, it has a minuscule cross section similarly to the neutrino particle. Many emerging theories hope to explain the mechanisms of production and interaction of dark matter and many future experiments hope to detect it. It is thought that the detection of dark matter will be more likely by producing boosted dark matter with the use of high energy particle accelerators, and since dark matter is also thought to interact similarly to the neutrino, the use of a neutrino detector also proves to be a good choice. These are all components of the Deep Underground Neutrino Experiment (DUNE) at Fermilab. This paper explores the possibility of detection in the low mass range of light dark matter at DUNE using electron elastic scatter events in the Near detector. We use computer simulations of dark matter and neutrinos produced in the experiment and their signals in the detector to set 90% confidence limits over the light dark matter parameter space.
THEORETICAL INVESTIGATIONS OF THE BULK AND SURFACE PROPERTIES OF PRISTINE AND DOPED PUO2
http://hdl.handle.net/10106/31671
THEORETICAL INVESTIGATIONS OF THE BULK AND SURFACE PROPERTIES OF PRISTINE AND DOPED PUO2
Plutonium oxides is of widespread significance due its application in nuclear fuels, space missions, as well as the long-termed storage of plutonium from spent fuel and nuclear weapons. The processes which refine and store plutonium bring many other elements in contact with the plutonium metal and thereby affect the chemistry of the plutonium. Pure plutonium metal corrodes to an oxide in air and the most stable form of this oxide is the stoichiometric plutonium dioxide, PuO2. Defects such as impurities and vacancies can form in the plutonium dioxide before, during and after the refining processes as well as during storage. Studying the interaction between transition metals and plutonium dioxide is critical for better, more efficient storage plans as well as gaining insights to provide a better response to potential threats of exposure to the environment.
Using density functional theory, first the bulk and then the PuO2 (111) surface of the pristine system have been investigated. The bulk results show that magnetic configurations of PuO2¬ are still debatable and need to be tested further in surface slabs. The pristine periodic slab models of the 110 and the 111 surface were examined to find surface properties and slab size effects. Surface modelling of up to six molecular layers were conducted. Ferromagnetic (FM) and anti-ferromagnetic (AFM) configurations were considered with and without spin-orbit coupling for the 1x1 slab. Furthermore, the effects of periodicity were explored between 1×1 and 2×2 super cell of the anti-ferromagnetic surface slabs. Results based on surface energies, work function, band gaps and density of states show that 5-6 molecular layer is sufficient for surface modelling. Except for the outer layer, the surface in general retains the Mott-insulator property.
Secondly the effects of impurity and defects in the bulk and then the PuO2 (111) surface have been investigated. Our study explores the interaction of a few key metals within the plutonium dioxide structure which have a likelihood of being exposed to the plutonium dioxide powder. We explored a doped system of substituted metal impurity within PuO2 supercell. We repeated the calculations with an additional oxygen vacancy. An impurity defect manifests itself at the bottom of the conduction band and affects the band gap of the unit cell. Our results reveal interesting volume contraction of PuO2 supercell when one plutonium atom is substituted with a metal atom. The volume of the doped system was further contracted with the addition of a single nearby oxygen vacancy.
Extending the impurity dopant to a 5 molecular layer 2x2 surface, three layers were highlighted. The outer layer, exposed to the vacuum, the bulk layer in the middle of the slab and the subsurface layer sandwiched between the bulk and the outer layer. Oxygen vacancy in the outer layer is less favorable than the bulk-layer and effects the Pu-Pu distances beyond the layer that it resides in. Zirconium impurity tested on each highlighted layer, has negative formation energy and has minimal impact on the slab beyond its nearest neighbor atoms. The non-pristine slab contracts due to dopants and defects as well but retains the Mott-insulating character with a zirconium impurity within the PuO2 (111) surface slab.