Resolving the Transition Between Galactic and Extragalactic Cosmic Rays with the Owens Valley Radio Observatory Long Wavelength Array

Developments in radio detection of high-energy particle showers over the last decade have demonstrated it to be a powerful technique to measure properties of ultra-high-energy cosmic rays. The Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) is now completing the commissioning of an extensive air shower detection mode that will significantly improve measurements of the cosmic ray energy spectrum in the Galactic-to-extragalactic source transition region. The award supports researchers at the California Institute of Technology (Caltech) and the Jet Propulsion Laboratory (JPL) to develop analyses for state-of-the-art high-energy cosmic ray detection that will provide the largest sample of radio detection events obtained to date. The team will pursue a multi-faceted program spanning broader impact activities for K-12 and undergraduate students. The team will collaborate with the JPL education office to engage high schools in the South Los Angeles area, and participate in Spanish-language outreach talks and lectures via the Caltech Astronomy Stargazing and Public Lecture Series. The OVRO-LWA will obtain a sample of approximately 24,000 radio observations of high-energy cosmic rays in the energy region central to where the anticipated sources transition from the Milky Way galaxy to those extragalactic. The OVRO-LWA observations are made possible by reduced uncertainties in the energy and mass composition measurement provided via the radio detection technique that will inform on the shape of the cosmic ray spectrum and mass composition shifts with energy in the transition region. The technique leverages the developments in radio detection of high-energy particle showers gained with the ANITA, LOFAR, and Pierre Auger Observatory, and proof-of-concept measurements with the OVRO-LWA. The studies will continue to advance radio tomographic analysis techniques that fully exploit the understanding of cosmic ray air showers and their radio emission. Finally, the OVRO-LWA cosmic ray dataset will enable new investigations of anisotropy measurements and searches for neutron sources. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.