Unveiling the Origin of Galactic Cosmic Rays: Exploring Pulsar Environments at the Highest Energies

• Applicant: Dr. Alison Mitchell
• Subject Area: Astrophysics and Astronomy
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 452934793

This project aims to unveil the origin of Galactic Cosmic Rays (CRs), a fundamental open problem in astrophysics, through studies of pulsar environments in gamma-ray energies. CRs are energetic charged particles, accelerated to high energies in extreme cosmic environments, which then traverse space and continuously bombard Earth.Galactic accelerators are thought to dominate the CR flux up to energies of 1 PeV, where a spectral hardening in the all particle CR spectrum known as the the `knee' occurs. Although the bulk of the CR flux is thought to be sustained by supernovae, experimental evidence for PeV particles in the vicinity of supernova remnants remains elusive. Within the last year, evidence has emerged that Pulsar Wind Nebulae (PWNe) accelerate electrons and positrons to PeV energies, but the origin of other PeV particles remains unconfirmed. Recent measurements of two nearby pulsars showed surprisingly slow CR diffusion, causing some tension with current theoretical models. This project will make significant steps in furthering our current knowledge of PWNe systems. Four main questions have been identified, that can be addressed by improving the performance of ground-based gamma-ray instruments at high energies towards 100 TeV and to extended sources with size greater than approximately 1 degree. These are: 1) What fraction of the PWNe population accelerate particles to PeV energies; 2) Do PWNe show evidence of accelerating hadronic as well as leptonic particles; 3) How are energetic particles transported through pulsar environments and into the ISM; and 4) Are `halos' of escaped particles a common feature of late-stage PWNe evolution? The unifying goal of this project is therefore to: "Unveil the pulsar contribution to the origin of Galactic Cosmic Rays"Within the the first phase of this project, the focus will be on technical improvements to data analysis and towards detailed and precision studies of individual PWNe systems, whilst in the second phase a major aim will be to increase the number of known TeV PWNe and halos, conducting multi-wavelength and population studies. The analysis improvements made will additionally benefit studies of other sources at the highest energies and of extended TeV gamma-ray emission. Similarly, the scientific results will feed into our understanding of CRs and their wider role within our Galaxy.

• DFG Programme: Independent Junior Research Groups