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Unveiling the footprints of the cosmic ray journey through the Galaxy and beyond
Unveiling the footprints of the cosmic ray journey through the Galaxy and beyond
PRIN: PROGETTI DI RICERCA DI RILEVANTE INTERESSE NAZIONALE – Bando 2022 - Prot. 2022TJW4EJ
Research Unit 1: Istituto Nazionale di Astrofisica (INAF) Elena Amato -- Research Unit 2: Gran Sasso Science Institute (GSSI) Pasquale Blasi
Project Abstract
The propagation of non-thermal particles in the acceleration region, in the vicinity of sources, through the Galaxy and even when escaping the host galaxies is affected by the particles themselves, through the excitation of instabilities that amplify the turbulence level in the ambient medium. The importance of such non-linear process is well established in the context of particle acceleration, where its effectiveness is key to explain the levels of magnetisation and the particle energies deduced from X-ray observations of powerful accelerators, as for example young Supernova Remnant (SNR) shocks. In the past few years, the idea that cosmic rays (CRs) modify the ambient plasma to ultimately rule their own transport has found support in a number of diverse observations. Examples are the breaks detected by PAMELA, AMS-02 and DAMPE in the spectra of galactic CRs, likely hints of a change in their diffusion properties, or the extended haloes of gamma-ray emission detected by HAWC around evolved Pulsar Wind Nebulae (PWNe), but also SNRs and star clusters.
Building on our previous work exploring non-linear CR transport in various contexts, and on the expertise in computational astrophysics within our team, this project aims at a quantitative assessment of the phenomenon, by means of numerical tools appropriate to deal with the multi-scale nature of the problem. We plan to investigate non-linear CR transport primarily by means of MHD+PIC simulations, in which the background fluid is treated within the MHD approximation while CRs are evolved according to kinetic equations. Different from the acceleration process that does not allow a separation of scales between CRs and thermal particles, unless a recipe for particle injection is a-priori assumed, the process of propagation entails a natural separation of scales, being the initial distribution in energy and space of the non-thermal particles determined by the source, and hence playing the role of a predefined injection term: the usage of a MHD+PIC approach is then well justified.
The specific physical problems we plan to investigate are: 1) escape of CRs from SNRs and star forming regions; 2) escape of electron-positron pairs from PWNe and their connection with the mysterious TeV halos and with the CR positron excess; 3) escape of CRs from the Galaxy into the intergalactic medium, where CR driven instabilities may confine particles in a turbulent bubble, possible source of multiple non-thermal radiations including gamma-rays and neutrinos; 4) escape of ultra-high energy CRs from their sources, including possible imprints of non-linear transport on their spectrum and on intergalactic magnetic fields. The project has a large potential of major breakthroughsin the field and its outcome will certainly affect our understanding of current observations and the planning of future observational campaigns, especially with reference to the upcoming Cherenkov Telescope Array and neutrino telescopes.
List of acknowledging works (being updated, for the ADS version click here)
Peron G. et al. 2024 "On the Correlation between Young Massive Star Clusters and Gamma-Ray Unassociated Sources", https://ui.adsabs.harvard.edu/abs/2024ApJ...972L..22P/abstract
Vecchiotti V. et al. 2025 "Interpreting the LHAASO Galactic diffuse emission data", https://ui.adsabs.harvard.edu/abs/2025JCAP...09..041V/abstract
Menchiari S. et al. 2025 "Contribution of young massive stellar clusters to the Galactic diffuse γ-ray emission", https://ui.adsabs.harvard.edu/abs/2025A%26A...695A.175M/abstract
Amato E. & Recchia S. 2024 "Gamma-ray halos around pulsars: impact on pulsar wind physics and galactic cosmic ray transport", https://ui.adsabs.harvard.edu/abs/2024NCimR..47..399A/abstract
Menchiari S. et al. 2024 "Cygnus OB2 as a test case for particle acceleration in young massive star clusters", https://ui.adsabs.harvard.edu/abs/2024A%26A...686A.242M/abstract
Olmi B. et al 2024 "The nature of X-ray filaments around bow shock pulsar wind nebulae", https://ui.adsabs.harvard.edu/abs/2024A%26A...686A.242M/abstract
de Oña Wilhelmi et al. 2024 "The hunt for PeVatrons as the origin of the most energetic photons observed in the Galaxy", https://ui.adsabs.harvard.edu/abs/2024NatAs...8..425D/abstract
Bourguinat et al. 2025 "The environment of TeV halo progenitors", https://ui.adsabs.harvard.edu/abs/2025arXiv250701495B/abstract
Blasi P. 2025 "Gamma radiation from cosmic rays escaping a young supernova remnant: The case of Cas A", https://ui.adsabs.harvard.edu/abs/2025A%26A...702A..24B/abstract
Sushch I. et al. 2025 "Supernova remnants in super bubbles acting as cosmic ray accelerators", https://ui.adsabs.harvard.edu/abs/2025A%26A...700A..37S/abstract
Schroer B. et al. 2025 "Critical examination of the nested leaky box model for Galactic cosmic ray transport", https://ui.adsabs.harvard.edu/abs/2025PhRvD.111l3003S/abstract
Ambrosone A. et al. 2025 "The origin of very high-energy diffuse γ-ray emission: The case for galactic source cocoons", https://ui.adsabs.harvard.edu/abs/2025A%26A...698L..18A/abstract
Blasi P. 2025 "Gamma rays from star clusters and implications for the origin of Galactic cosmic rays", https://ui.adsabs.harvard.edu/abs/2025A%26A...694A.244B/abstract
Bandiera R. & Petruk O. 2024 "Synchrotron polarization with a partially random magnetic field: General approach and application to X-ray polarization from supernova remnants", https://ui.adsabs.harvard.edu/abs/2024A%26A...689A.137B/abstract
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