The Origin Of High Energy Neutrinos And Ultrahigh Energy Cosmic Rays

Ultrahigh energy cosmic rays are extraterrestrial energetic particles with energy above 1018eV. However, due to the rarity of events and the complexity in their propagation to Earth, people have not got a deep understanding through the direct measurement on ultrahigh energy cosmic rays so far. And hence, it is useful to extract some additional information from the observation on the secondary particles (such as neutrinos) which are generated in the propagation of ultra-high energy cosmic rays. Recently, IceCube neutrino observatory has discovered 54 neutrino events with energy from 60TeV to 3PeV, opening an new era of neutrino astronomy. In this thesis, we investigate the astrophysical origin of these neutrinos and their possible link with ultrahigh energy cosmic rays. In the first chapter, we briefly introduce the related background knowledge, including IceCube neutrino observatory and their observations, neutrino produc-tion process, as well as the observation of ultrahigh energy cosmic rays and candidate sources. In Chapter 2, we discuss the general requirement for these neutrinos originating from the same sources of ultrahigh energy cosmic rays. Based on the requirement, we can exclude some mod-els. In Chapter 3, we look into details that whether gamma-ray bursts can be the sources of the observed neutrinos. First, we correct the overestimation on the expected neutrino flux from gamma-ray bursts by IceCube Collaboration. And then we discuss that whether the "dim GRB-s", which are not able to trigger current GRB detectors, can contribute the observed neutrinos. In Chapter 4, we propose semi-relativistic hypernova remnants in star-forming galaxies as the common sources of ultrahigh energy cosmic rays. We calculate the propagated spectrum of ultrahigh energy cosmic rays throughout the whole universe with considering the interaction in their propagation in the intergalactic space. We find the obtained spectrum and mass composi-tion of ultrahigh energy cosmic rays are consistent with observations. In Chapter 5, we study the propagation of ultrahigh energy cosmic rays in magnetic fields and constrain the source distance and metallicity by jointly using the observation of PAO on chemical composition and distribution of arrival directions. In Chapter 6, we model the multiwavelength light curves of GRBs’ afterglows and study the origin of the prompt and extended high energy radiation. In the last chapter, we give a summary and discussion of the thesis, and also point out some feasible successive work.