The Probe Of Multi-Messenger Astrophysics (POEMMA)
Abstract: Thanks to giant extensive air-showers observatories, such as the Pierre Auger Observatory and the Telescope Array (TA), we now know that the sources of ultrahigh energy cosmic rays (UHECRs) are extragalactic. We also learned that their spectrum show features of the source maximum energy or the interactions with the cosmic microwave background. Their composition is either surprising (dominated by heavier nuclei at the highest energies) or the hadronic interactions at 100 TeV are not a standard extrapolation of LHC energies. Hints of anisotropies begin to appear as energies above ~ 60 EeV, just when statistics become very limited on the ground.
A significant increase in the statistics of UHECRs observations above 60 EeV and the discovery of neutrinos (and possibly gamma-rays) at EeV energies, are needed to answer: What cosmic objects generate such extremely energetic particles that reach 10^20 eV (100 EeV)? What is their composition and how do their reach these extreme energies? How do they interact on their way to Earth and with the Earth’s atmosphere? What neutrino and gamma-ray flux do they generate?
An international collaboration built the Extreme Universe Space Observatory (EUSO) on a super pressure balloon (SPB) to be the first to detect UHECR fluorescence from above. EUSO-SPB is about to launch from New Zealand. We are now designing POEMMA, a probe class space mission designed to solve the mystery at the extreme energy cosmic frontier.