Date of Award
Doctor of Philosophy (PhD)
Physics and Astronomy
Dr. Dieter Hartmann
Dr. Bradley Meyer
Dr. Marco Ajello
Dr. Xian Lu
Cosmic Multi-Messenger backgrounds include relic diffuse components created in the early Universe and contributions from individual sources. In this dissertation, I present the work done in Anandagoda (2019); Anandagoda et al. (2020, 2023) where type Ia (SNe Ia) and core-collapse supernovae (CCSNe) contributions to the diffuse neutrino and gamma-ray backgrounds in the MeV regime are studied. These backgrounds are referred to as DSNB and DSGB respectively. Based on this work, the diffuse SN Ia background is ~106 times lower (for electron antineutrinos) than the CCSN background making it negligible. The predicted DSNB electron antineutrino flux at earth in the 19.3-32 MeV regime is 0.36 ν cm-2s-1. We also find that the DSNB flux in the energy range from 11.3 - 32 MeV varies by ≈+29\% with a change in the SFRD model from Madau and Fragos (2017) which yielded a minimum predicted flux, to EBL reconstruction model (Fermi-LAT Collaboration et al., 2018) (maximum predicted flux).
The diffuse SN Ia gamma-ray background and its dependence on the progenitor-supernova delay time distribution (DTD) is also evaluated. Furthermore, we address the origin of the CGB (Cosmic Gamma-ray Background) in the 0.1-7 MeV regime by adding contributions from sources such as SNe Ia, CCSNe, radio-quiet Active Galactic Nuclei (AGN), Flat spectrum radio quasars (FSRQs) and Neutron star - neutron star (NS-NS) mergers. We find that our modeled background (including uncertainties) matches the observed CGB above 1.0 MeV, but is a factor ≈2 lower than the observed flux in the 0.1 MeV to 1.0 MeV range, highlighting the need for future MeV missions to establish the CGB spectrum more reliably, and to possibly identify additional sources or even source classes in the under-explored MeV band.
While solar neutrino spectra have been studied extensively, neutrino spectra from other stars have not been the subject of detailed studies. In this work, the change in the electron neutrino spectra for various stars of different masses and ages are evaluated using stellar models evolved using Modules for Experiments in Stellar Astrophysics (MESA) simulation software. Based on these results, the electron neutrino spectrum from the Milky Way galaxy is modeled.
Anandagoda, Ilukpitiye Samalka, "Cosmic Diffuse Neutrino and Gamma-Ray Backgrounds in the MeV Regime" (2023). All Dissertations. 3412.
Author ORCID Identifier
Cosmology, Relativity, and Gravity Commons, External Galaxies Commons, Other Astrophysics and Astronomy Commons, Physical Processes Commons, Stars, Interstellar Medium and the Galaxy Commons, The Sun and the Solar System Commons