From the Galaxy to the Edge of the Universe: Plausible Sources of UHECRs

The lack of a high energy cutoff in the cosmic ray spectrum together with an apparently isotropic distribution of arrival directions for the highest energy events have strongly constrained most models proposed for the generation of these particles. An overview of the theoretical proposals are presented along with their most general signatures. Future experimental tests of the different proposals are discussed.Comment: 14 pages, 7 figures; talk given at the International Workshop on Observing Ultra High Energy Cosmic Rays From Space and Earth, Metepec, Puebla, Mexico (2000

POEMMA (Probe of Extreme Multi-Messenger Astrophysics) Roadmap Update

The Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) was designed as a NASA Astrophysics probe-class mission to identify the sources of ultrahigh energy cosmic rays (UHECRs) and observe cosmic neutrinos from extremely energetic transient sources. POEMMA consists of two identical spacecraft flying in a loose formation at 525 km altitude oriented to view a common atmospheric volume and to provide full-sky coverage for both types of messengers. Each spacecraft hosts a wide field of view Schmidt telescope with a hybrid focal plane optimized to observe both the UV fluorescence signal from extensive air showers (EASs) and the optical Cherenkov signals from EASs. When in stereo close to nadir mode, POEMMA can measure the spectrum, composition, and full-sky distribution of the UHECRs above 20 EeV and be sensitive to UHE neutrinos. When pointing just below the Earth's limb, POEMMA will be sensitive to cosmic tau neutrinos above 20 PeV by observing the Cherenkov radiation of EASs produced by upward-moving tau decays, induced from tau neutrino interactions in the Earth. POEMMA is designed to quickly re-orient to follow a Target-of-Opportunity (ToO) neutrino transient from astrophysical sources with exceptional sensitivity to neutrinos from both short-duration transients, such as short-gamma-ray bursts (sGRBs), and long-duration sources, such as binary neutron star (BNS) mergers. Here we review the POEMMA mission and discuss the recent progress towards its technical readiness provided by the Mini-EUSO and EUSO-SPB2 missions and the forthcoming Terzina and POEMMA-Balloon-Radio missionsComment: 12 pages, 5 figures, Proceeding 38th ICRC 2023 Nagoya, Japan. arXiv admin note: substantial text overlap with arXiv:1909.0946