   First- and second-order Fermi acceleration in thick relativistic shocksMeli, Athina  in AIP Conference Proceedings (2012) Shocks in relativistic jets are regions where cosmic ray acceleration takes place mainly via two kinds of Fermi acceleration mechanism: The first-order and the second-order Fermi acceleration. Moreover ... [more ▼] Shocks in relativistic jets are regions where cosmic ray acceleration takes place mainly via two kinds of Fermi acceleration mechanism: The first-order and the second-order Fermi acceleration. Moreover, the back-reaction of accelerated particles in astrophysical shock fronts leads to the formation of a precursor (thick) shock with a length scale which can correspond to the diffusive scale of the energetic particles. Our scope here is to investigate the properties of particle shock acceleration, using test-particle simulation studies, assuming stochastic and diffusive acceleration mechanisms, in thick parallel and perpendicular relativistic shocks. The role of the above parameters in the acceleration efficiency and generated cosmic ray spectra, is important to understanding further the favourable subject of the cosmic ray shock acceleration in relativistic astrophysical environments. [less ▲] Detailed reference viewed: 8 (1 ULg)Neutrinos from photo-hadronic interactions in Pks2155-304; Meli, Athina ; in Nuclear Instruments & Methods in Physics Research Section A (2011) The high-peaked BL Lac object Pks2155-304 shows high variability at multiwavelengths, i.e. from optical up to TeV energies. A giant flare of around 1 h at X-ray and TeV energies was observed in 2006 [1 ... [more ▼] The high-peaked BL Lac object Pks2155-304 shows high variability at multiwavelengths, i.e. from optical up to TeV energies. A giant flare of around 1 h at X-ray and TeV energies was observed in 2006 [1]. In this context, it is essential to understand the physical processes in terms of the primary spectrum and the radiation emitted, since high-energy emission can arise in both leptonic and hadronic processes. In this contribution, we investigate the possibility of neutrino production in photo-hadronic interactions. In particular, we predict a direct correlation between optical and TeV energies at sufficiently high optical radiation fields. We show that in the blazar Pks2155-304, the optical emission in the low-state is sufficient to lead to photo-hadronic interactions and therefore to the production of high-energy photons. [less ▲] Detailed reference viewed: 10 (6 ULg)Active Galactic Nuclei and Gamma Ray Bursts: Relativistic shocks and the origin of ultra high energy cosmic raysMeli, Athina ; ; in Nuclear Instruments & Methods in Physics Research Section A (2011) Detailed reference viewed: 8 (2 ULg) Numerical modeling of relativistic shock accelerationMeli, Athina in Astrophysics & Space Sciences Transactions : ASTRA (2011) The shock acceleration mechanism is invoked to explain non-thermal cosmic rays in Supernova Remnants, Active Galactic Nuclei and Gamma Ray Bursts jets. Especially, the importance of relativistic shock ... [more ▼] The shock acceleration mechanism is invoked to explain non-thermal cosmic rays in Supernova Remnants, Active Galactic Nuclei and Gamma Ray Bursts jets. Especially, the importance of relativistic shock acceleration in extragalactic sources is a recurring theme raising a significant interest in the research community. We will briefly discuss the shock acceleration mechanism and we will address the properties of non-relativistic and relativistic shocks, particularly focusing on relativistic numerical Monte Carlo studies. [less ▲] Detailed reference viewed: 32 (15 ULg) |
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