Cosmic Gold Mining: Hunting for the Astrophysical Sites of r-Process Nucleosynthesis

Author: Anand, Shreya

Year: 2024

Degree: Dissertation (Ph.D.)

Advisor: Kasliwal, Mansi M.

Committee Members: Fuller, James; Mawet, Dimitri; Weinstein, Alan Jay; Chatziioannou, Katerina; Kasliwal, Mansi M.

Option: Physics

DOI: 10.7907/145k-w841

Abstract

One of the major open questions in astronomy is where the heaviest elements in the Universe are formed. These elements, generated via the rapid neutron-capture process (r-process), require environments abundant with free neutrons, present only in extreme cosmic explosions, which are by nature inherently rare. To date, vivid, direct evidence of heavy element nucleosynthesis has been seen and most extensively studied in the binary neutron star (BNS) merger GW170817. However, neutron star–black hole (NSBH) mergers, some collapsing massive stars (collapsars), and other explosions have also been proposed as alternative sites of r-process production. This thesis explores BNS mergers, NSBH mergers, and collapsars as r-process sites through observational studies. In this work, we first investigate whether r-process signatures are present in the light curves of broadlined type Ic supernovae (SNe Ic-BL) associated with long-duration gamma-ray bursts. For this study, we conduct optical imaging with the Zwicky Transient Facility (ZTF) and near-infrared imaging with the Wide-Field Infrared Camera on the Palomar 200-in Hale telescope of ZTF-discovered SNe Ic-BL. Second, we study the chemical distribution of ejecta in the kilonova (KN)---an optical/near-infrared transient powered by the radioactive decay of r-process elements---counterpart to GW170817, using new state-of-the-art KN models and incorporating precise inclination information on GW170817 into our inference. Third, we describe systematic searches conducted with ZTF for KNe associated with both BNS and NSBH mergers detected by the LIGO Virgo KAGRA detector network during its third and fourth observing runs. Based on our non-detections, we place constraints on the properties of KNe from both BNS and NSBH merger sites. Finally, we summarize the unique insights we have gained on the nature of r-process sites from observations and non-detections. We also discuss prospects for discovering and characterizing these transients with upcoming surveys such as the Vera C. Rubin Observatory and the Nancy Grace Roman Space Telescope.

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