Article
Astronomy & Astrophysics
P. Rashed-Mohassel, M. Ghorbanalilu
Summary: The study investigates the scatter-free acceleration of a test particle thrusted by a moving magnetized cloud in the presence of the uniform interstellar magnetic field. It reveals three different scenarios for the interacting particles depending on the orientation of the background magnetic field. Trapped particles gain energy through magnetic trapping acceleration, while injected particles accelerate through a spiral acceleration mechanism until located inside the cloud, suggesting the importance of spiral acceleration in cases where trapping conditions are not met.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Jun Fang, Qi Xia, Shiting Tian, Liancheng Zhou, Huan Yu
Summary: Non-relativistic quasi-parallel shocks have the potential to accelerate electrons, protons, and helium ions. A 1D particle-in-cell simulation of a non-relativistic quasi-parallel shock with a helium-to-proton number density ratio relevant to Galactic cosmic rays reveals that energetic protons and helium ions can excite waves upstream of the shock, leading to the scattering and gradual acceleration of charged particles. The downstream spectra of charged particles are thermal with a non-thermal tail, and a significant amount of kinetic energy is transferred to non-thermal protons and helium ions.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
T. Vieu, S. Gabici, V Tatischeff, S. Ravikularaman
Summary: We study the production of cosmic rays in dynamical superbubbles formed by a cluster of massive stars. Stellar winds, supernova remnants, and turbulence efficiently accelerate particles, and their nonlinear feedback is important for maintaining energy balance. High-energy particles escape quickly after each supernova explosion, while low-energy particles are stochastically accelerated and harden the spectra. The presence of a magnetized shell enhances the confinement of cosmic rays in the bubble. We estimate the overall contribution of superbubbles to Galactic cosmic ray content and present the expected gamma-ray spectra from hadronic interactions in superbubble shells.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
T. Vieu, S. Gabici, V Tatischeff
Summary: The linear theory of diffusive shock acceleration breaks down when the pressure of particles accelerated at shock waves becomes significant compared to the kinetic pressure of the gas. Non-linear backreaction of particles on the magnetohydrodynamic flow needs to be taken into account in order to describe these systems. The presence of pre-existing energetic particles strongly affects the shock profile and reduces the efficiency of reaccelerating non-thermal particles. The study of the evolution of particle distribution after multiple shocks indicates that the spectrum converges towards a concave solution and the post-shock cosmic ray pressure only accounts for a small fraction of the shock pressure.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Zhi-Qiu Huang, Brian Reville, John G. Kirk, Gwenael Giacinti
Summary: We conducted test-particle Monte Carlo simulations to study the acceleration of charged particles by ultra-relativistic shocks. Two field configurations were considered: shocks with uniform upstream magnetic field and shocks with cylindrical upstream magnetic field. The particles were assumed to diffuse in angle due to frequent non-resonant scattering. The distribution of particles' Lorentz factors was found to approximately follow dN/d gamma proportional to gamma(-2.2) when the particle motion was scattering dominated on at least one side of the shock. The acceleration rate scaled as t(acc) proportional to t(1/2) for scattering dominated transport, but recovered Bohm scaling t(acc) proportional to t if particles became magnetized on one side of the shock. A limiting energy was reached for uniform field configurations when particles were magnetized on both sides of the shock, but this limit did not apply to cylindrical field configurations. In the cylindrical field configuration, particles of one sign of charge experienced a curvature drift that redirected particles upstream. The distribution approached the escapeless limit dN/d gamma proportional to gamma(-1) when particles reached the confinement limit determined by the finite system size. The cylindrical field configuration resembled that expected for jets launched by the Blandford & Znajek mechanism, implying the potential of active galactic nuclei and gamma-ray bursts as sites for the production of ultra-high-energy cosmic rays.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
L. Yang, V. Heidrich-Meisner, L. Berger, R. F. Wimmer-Schweingruber, L. Wang, J. He, X. Zhu, D. Duan, A. Kollhoff, D. Pacheco, P. Kuehl, Z. Xu, D. Keilbach, J. Rodriguez-Pacheco, G. C. Ho
Summary: This study aims to determine the properties of suprathermal protons accelerated by interplanetary shocks. The results show that the proton fluxes peak before the shock and rapidly decrease in a thin layer adjacent to the shock. The velocity distribution function of these protons follows a double power law, suggesting that shock-drift acceleration plays an important role in their acceleration.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Physics, Fluids & Plasmas
Francesco Malara, Silvia Perri, Gaetano Zimbardo
Summary: The study investigates the interaction between charged particles and an ideal magnetohydrodynamics rotational discontinuity, showing that the motion of particles crossing the discontinuity is extremely complex and highly sensitive to initial conditions. Particles can be temporarily trapped in rotational discontinuity, and the separatrix in the initial conditions phase space between crossing and noncrossing trajectories has a fractal structure.
Article
Astronomy & Astrophysics
A. Fazzini, W. Yao, K. Burdonov, J. Beard, S. N. Chen, A. Ciardi, E. D'Humieres, R. Diab, E. D. Filippov, S. Kisyov, V Lelasseux, M. Miceli, Q. Moreno, S. Orlando, S. Pikuz, X. Ribeyre, M. Starodubtsev, R. Zemskov, J. Fuchs
Summary: This study investigates the effect of the interpenetration between two subcritical collisionless shocks on particle energization through experimental and computational work. The results show that the presence of two shocks leads to higher energy levels in ambient ions compared to a single shock. The downstream zones of the shocks play a crucial role in this different energization process.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
V. N. Zirakashvili, V. S. Ptuskin
Summary: This study investigates diffusive shock acceleration in supernova remnants, considering their evolution including a radiative stage. It is found that a more efficient acceleration and fast exit of particles during the radiative stage result in the hardening of the source cosmic ray proton and electron spectra at energies similar to 100-500 GeV. The effect is stronger for cosmic ray electrons.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Krzysztof Stasiewicz, Zbigniew Klos
Summary: The analysis of four-point measurements by NASA's Magnetospheric Multiscale spacecraft reveals that the formation of quasi-parallel shocks is consistent with the counter-streaming ion-ion resonant right-handed instability. The onset of the instability is initiated by 30-second period oscillations, which steepen to shorter wavelengths and higher frequencies. The instability produces large amplitude magnetic field and plasma density shocklets with specific scale lengths.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Krzysztof Stasiewicz, Bengt Eliasson
Summary: Research shows that ions can be accelerated to high energies perpendicular to the magnetic field through the ExB mechanism, which is related to instabilities caused by density gradients and electron drift. The maximum energy of ions is proportional to the atomic mass number.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Ofir Arad, Assaf Lavi, Uri Keshet
Summary: The study identifies a specific sub-population of PWNe with hard spectra, possibly due to recent evacuation of the shock surroundings. The hard spectrum sub-population suggests a Fermi process, such as diffusive shock acceleration, at its extreme.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Krzysztof Stasiewicz, Bengt Eliasson
Summary: We demonstrate that quasi-adiabatic electron heating in quasi-perpendicular shocks is supported by measurements obtained from NASA's MMS mission, with the temperature Te perpendicular to proportional to B1 + α, where B is the magnetic field strength and α represents departure from adiabaticity. Our findings show that most situations exhibit negative α, resulting in a redistribution of perpendicular energy gain from adiabatic heating to the parallel direction, leading to a lower isotropic temperature increase. However, positive α is observed in cases where the stochastic heating of electrons is activated by the E x B wave acceleration mechanism, resulting in a higher temperature increase.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Benoit Cerutti, Gwenael Giacinti
Summary: By considering the global transverse structure of relativistic magnetized shocks, this study shows that the termination shock forming at the interface with the ambient medium can accelerate particles up to the confinement limit, supporting the idea that extragalactic plasma jets may be capable of producing ultra-high-energy cosmic rays.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Physics, Fluids & Plasmas
M. Miceli
Summary: Supernova remnants (SNRs) provide astrophysical labs for studying collisionless shocks and nonthermal processes. Different particle species in SNRs may be heated at different temperatures, and nonthermal emissions from shock fronts are caused by accelerated cosmic rays. X-ray spectroscopy can be used to study heating mechanisms and particle acceleration in collisionless shocks. Temperature measurements in SN 1987A and evidence of shock modification in SN 1006 a.D. have been obtained.
PLASMA PHYSICS AND CONTROLLED FUSION
(2023)