Dipartimento di Fisica

Descrizione del progetto

Understanding the extreme physical environments that characterize high-energy non-thermal astrophysical sources is key to interpreting the energetic phenomena that occur in Active Galactic Nuclei, pulsars and gamma-ray bursts. High-energy astrophysical phenomena involve, in general, magnetized relativistic flows, whose energy flux (kinetic and/or magnetic) can be partly converted, at dissipation sites, into random relativistic motion of particles that lose their energy through a variety of non-thermal processes and give rise to the observed radiation. The interpretation of the observed phenomenology therefore requires a detailed description of the highly nonlinear interactions between plasmas, non thermal relativistic particles and radiation. Despite the many advancements in the understanding of the basic processes involving these components, further progresses are hampered by the need of considering the interplay of processes occurring on a wide range of spatial and temporal scales.
The approach up to now has been forced to be sectorial. Models of the large scale dynamics can be obtained through relativistic magnetohydrodynamical (RMHD) numerical simulations. In these simulations, however, the relativistic particle component is not considered, dissipation sites are treated in a rather crude way and it is therefore impossible to make predictions on the observed radiation. The generation of relativistic particles is studied through kinetic numerical simulations (Particle In Cell codes), that provide fundamental insights on the detailed physics of the acceleration process, but cover only tiny spatial domains and time spans, keeping fixed the large scale structure, which is prescribed as a boundary conditions. Finally, phenomenological models can provide detailed predictions to be compared with observational data, but, are based on ad hoc or very simplifying assumptions. As a consequence, the resulting picture is incomplete and fragmentary.
Given the complex physical picture and the strong nonlinearities involved in its description, a numerical approach is unavoidable. As we said. a fundamental present weakness of this approach is the large gap between the results obtained from simulations and the observational signatures of the astrophysical systems. With this proposal we intend to bridge this gap. This task requires the coupling of the large scale dynamics with a detailed treatment of the microphyiscs at dissipation sites, an extremely challenging task that only now is becoming feasible thanks to the advancements of high performance computing. The final goal of this project is then the foundation of an innovative virtual laboratory for non-thermal astrophysical radiation that will be used for the study and interpretation of high energy astrophysical sources. In order to accomplish this project it is necessary to combine widely different expertises in theoretical, numerical, phenomenological modeling and observations.