Cosmic Ray Acceleration in Astrophysical Systems

• Grant number: 25/12301-2
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: November 01, 2025
• End date: October 31, 2027
• Field of knowledge: Physical Sciences and Mathematics - Astronomy
• Principal Investigator: Elisabete Maria de Gouveia Dal Pino
• Grantee: Petros Stefanou
• Host Institution: Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 21/02120-0 - Investigation of high energy and plasma astrophysics phenomena, installation of the ASTRI-Mini Array & construction of the Cherenkov Telescope Array Small Size Telescopes (CTA-SSTs), AP.ESP

Abstract

Cosmic rays (CRs), spanning energies from 10^9 to 10^20 eV, are produced in diverse astrophysical systems, yet their acceleration mechanisms remain only partially understood. While lower-energy CRs are Galactic, the origins of ultra-high-energy CRs are still debated. Gamma-ray astronomy serves as a critical tool to study CR production, as charged particles are deflected by magnetic fields, obscuring their sources. Upcoming observatories like the CTA and the ASTRI Mini-Array are well-equipped to explore these processes with unprecedented sensitivity. This project focuses on particle acceleration via magnetic reconnection, a mechanism increasingly recognized as crucial in astrophysical plasmas. Reconnection efficiently converts magnetic energy into particle energy, producing power-law energy distributions observed in high-energy emissions from sources such as supernova remnants (SNRs), active galactic nuclei (AGNs), and gamma-ray bursts (GRBs). Recent numerical studies reveal that reconnection acceleration is efficient across a range of conditions, offering a universal mechanism complementary to shock and stochastic acceleration, where the latter are found to be less efficient or absent. Using advanced numerical simulations, including MHD, PIC, hybrid approaches, and AI, this study will: (1) explore reconnection acceleration mechanisms, (2) derive acceleration and diffusion rates, (3) study radiative losses and spectral properties, (4) incorporate time-dependent MHD environments for turbulent acceleration, and (5) examine reconnection in relativistic systems like black hole jets. These efforts aim to model flares and spectra of astrophysical sources, providing key insights for interpreting CTA and ASTRI observations. This research will enhance our understanding of CR acceleration, advancing both theoretical frameworks and observational predictions for high-energy astrophysics. (AU)