Cosmic Ray Indirect Rapporteur Report (37th ICRC )

Abstract

This report summarizes the physics results presented as part of the cosmic-ray indirect (CRI) session of the 37 th ICRC conference. Updated measurements on cosmic-ray energy spectrum, mass composition, and arrival direction distributions were presented by several collaborations, spanning the energy range of a few TeV up to the highest observed energies. We select some of the results which were highlighted by the respective discussion leaders or which presented new results at this conference. Results on atmospheric phenomena, including TGFs and thunderstorms are also presented. We see a few interesting trends in the presented data. Among these are, the increased use of IACT's to study cosmic-rays among experiments primarily intended for gamma-ray measurements. Another, is the continued development of radio detection of air showers. Multi-component detectors are becoming the preferred detection mode, as the knowledge of how to integrate the different information about an air shower collected by the different detector components improves. The main physics questions about the origins of cosmic rays, both galactic and extra-galactic, remain open. Increased statistics and improved analyses allow for refining and better constraining theoretical models, but no definitive answers can be claimed thus far. Looking forward, the field is moving at a rapid pace; Several detectors upgrades are underway, data is continually coming in and analyzed, old data being made public for a wider audience and a new generation of scientists to examine, with new tools and approaches that will hopefully result in new insights to help solve the open questions on cosmic-rays.

The second knee in the cosmic ray spectrum observed with the surface detector of the Pierre Auger Observatory

“…The concept that the Galactic-to-extragalactic transition occurs between 100 PeV and a few EeV is well-accredited [1][2][3][4][5]. It is thus to be expected that different astrophysical phenomena are at play in this energy region, that overlap and intertwine with each other.…”

Using TeV Cosmic Rays to probe the Heliosphere's Boundary with the Local Interstellar Medium

“…Modern operating and future ground-based CR observatories are designed to collect a large number of shower events up to ultra-high energies, with unprecedented statistical accuracy and increasing experimental precision 11 . The energy, mass, and arrival direction distribution of high energy CRs provide observational hints of the complex environment through which CRs propagate from their sources to Earth: the source turbulent environment, the injection into the ISM and propagation through interstellar turbulence, and the effects of coherent magnetic structures, such as the Local Bubble and the heliosphere.…”