Cosmic-ray Air Showers
Cosmic rays are charged particles–the nuclei of atoms—travelling at nearly the speed of light and reaching Earth from other parts of our Galaxy or other galaxies. Some cosmic rays accelerate to energies millions of times higher than the highest energies that can be achieved in human-made particle accelerators on Earth.
The astrophysical accelerators responsible for these particles are difficult to find, because charged particles wind around the Milky Way’s magnetic field, until their arrival trajectory can’t point back to their origins. Most cosmic rays in the Milky Way likely accelerate in supernova remnants, while the highest-energy particles probably originate outside our galaxy. There may be another, unidentified type of accelerators within our Milky Way Galaxy that produces the Galaxy’s highest-energy cosmic rays. The OVRO-LWA will study the composition of cosmic rays at the highest-energy limits of Galactic accelerators.
When a cosmic ray collides with Earth’s atmosphere, it produces a cascading shower of particle collisions. The charged particles in the shower produce radio waves which can be observed from the ground. The OVRO-LWA will study high-energy cosmic rays by searching for roughly 10-nanosecond flashes of radio waves that sweep across the array with the signature pattern of a cosmic ray. Detecting and classifying cosmic rays from the radio data alone requires novel signal processing infrastructure to sift through 176 gigabytes per second of raw data to save short snapshots of air-shower events.
The OVRO-LWA cosmic ray search will operate simultaneously with the regular astronomy observations, allowing nearly full-time cosmic ray observations. We expect to detect 2000-10000 cosmic rays per year in the energy range ~ 1017 – 1018 eV. We plan to analyze the composition of the sample with estimates of the column height of the shower maximum, Xmax, constrained to better than 20 g/cm2.