Diffusive Shock Acceleration of Cosmic Rays and Gamma Radiation from Young Supernova Shells

1990 ◽  
pp. 169-177
Author(s):  
V. S. Berezinsky ◽  
V. S. Ptuskin
Keyword(s):  
Cosmic Rays ◽  
Gamma Radiation ◽  
Shock Acceleration ◽  
Diffusive Shock Acceleration

scholarly journals Particle acceleration in winds of star clusters

2021 ◽  
Author(s):  
G Morlino ◽  
P Blasi ◽  
E Peretti ◽  
P Cristofari
Keyword(s):  
Particle Acceleration ◽  
Cosmic Rays ◽  
Supernova Remnants ◽  
Star Clusters ◽  
Cosmic Ray ◽  
Maximum Energy ◽  
Termination Shock ◽  
Shock Acceleration ◽  
Acceleration Process ◽  
Diffusive Shock Acceleration

Abstract The origin of cosmic rays in our Galaxy remains a subject of active debate. While supernova remnant shocks are often invoked as the sites of acceleration, it is now widely accepted that the difficulties of such sources in reaching PeV energies are daunting and it seems likely that only a subclass of rare remnants can satisfy the necessary conditions. Moreover the spectra of cosmic rays escaping the remnants have a complex shape that is not obviously the same as the spectra observed at the Earth. Here we investigate the process of particle acceleration at the termination shock that develops in the bubble excavated by star clusters’ winds in the interstellar medium. While the main limitation to the maximum energy in supernova remnants comes from the need for effective wave excitation upstream so as to confine particles in the near-shock region and speed up the acceleration process, at the termination shock of star clusters the confinement of particles upstream in guaranteed by the geometry of the problem. We develop a theory of diffusive shock acceleration at such shock and we find that the maximum energy may reach the PeV region for powerful clusters in the high end of the luminosity tail for these sources. A crucial role in this problem is played by the dissipation of energy in the wind to magnetic perturbations. Under reasonable conditions the spectrum of the accelerated particles has a power law shape with a slope 4÷4.3, in agreement with what is required based upon standard models of cosmic ray transport in the Galaxy.

scholarly journals Bohm Diffusion and Cosmic-Ray-Modified Shocks

1994 ◽  
Vol 142 ◽  
pp. 981-983
Author(s):  
Peter Duffy
Keyword(s):  
Particle Acceleration ◽  
Cosmic Rays ◽  
Cosmic Ray ◽  
Shock Acceleration ◽  
Back Reaction ◽  
Acceleration Of Particles ◽  
Diffusive Shock Acceleration ◽  
Spacetime Structure ◽  
Wide Range ◽  
Self Consistent

AbstractA numerical solution to the problem of self-consistent diffusive shock acceleration is presented. The cosmic rays are scattered, accelerated and exert a back-reaction on the gas through their interaction with turbulence frozen into the local fluid frame. Using a grid with a hierarchical spacetime structure the physically interesting limit of Bohm diffusion (к ∝ pv), which introduces a wide range of diffusion lengthscales and acceleration timescales, can be studied. Some implications for modified shocks and particle acceleration are presented.Subject headings: acceleration of particles — cosmic rays — diffusion — shock waves

scholarly journals Manufacturing cosmic rays in the evolving dynamical states of galaxy clusters

2019 ◽  
Vol 488 (1) ◽  
pp. 1301-1319 ◽  
Author(s):  
Reju Sam John ◽  
Surajit Paul ◽  
Luigi Iapichino ◽  
Karl Mannheim ◽  
Harish Kumar
Keyword(s):  
Cosmic Rays ◽  
Galaxy Clusters ◽  
Theoretical Calculations ◽  
Shock Acceleration ◽  
Diffusive Shock Acceleration ◽  
X Ray ◽  
Mass Scaling ◽  
Dynamical Phase ◽  
The Galaxy ◽  
High Mach

ABSTRACT Galaxy clusters are known to be reservoirs of cosmic rays (CRs), as inferred from theoretical calculations or detection of CR-derived observables. CR acceleration in clusters is mostly attributed to the dynamical activity that produces shocks. Shocks in clusters emerge out of merger or accretion, but which one is more effective in producing CRs? at which dynamical phase? and why? To this aim, we study the production or injection of CRs through shocks and its evolution in the galaxy clusters using cosmological simulations with the enzo code. Particle acceleration model considered here is primarily the Diffusive Shock Acceleration (DSA) of thermal particles, but we also report a tentative study with pre-existing CRs. Defining appropriate dynamical states using the concept of virialization, we studied a sample of merging and non-merging clusters. We report that the merger shocks (with Mach number $\mathcal {M}\sim 2-5$) are the most effective CR producers, while high-Mach peripheral shocks (i.e. $\mathcal {M}\gt 5$) are mainly responsible for the brightest phase of CR injection in clusters. Clusters once merged, permanently deviate from CR and X-ray mass scaling of non-merging systems, enabling us to use it as a tool to determine the state of merger. Through a temporal and spatial evolution study, we found a strong correlation between cluster merger dynamics and CR injection. We observed that the brightest phase of X-ray and CR injection from clusters occurs, respectively, at about 1.0 and 1.5 Gyr after every mergers, and CR injection peaks near to the cluster virial radius (i.e r200). Delayed CR injection peaks found in this study deserve further investigation for possible impact on the evolution of CR-derived observables from galaxy clusters.

scholarly journals Cosmic rays and stochastic magnetic reconnection in the heliotail

2012 ◽  
Vol 19 (3) ◽  
pp. 351-364 ◽  
Author(s):  
P. Desiati ◽  
A. Lazarian
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Magnetic Reconnection ◽  
Supernova Remnants ◽  
Average Energy ◽  
Cosmic Ray ◽  
Galactic Cosmic Rays ◽  
Shock Acceleration ◽  
Diffusive Shock Acceleration ◽  
The Galaxy

Abstract. Galactic cosmic rays are believed to be generated by diffusive shock acceleration processes in Supernova Remnants, and the arrival direction is likely determined by the distribution of their sources throughout the Galaxy, in particular by the nearest and youngest ones. Transport to Earth through the interstellar medium is expected to affect the cosmic ray properties as well. However, the observed anisotropy of TeV cosmic rays and its energy dependence cannot be explained with diffusion models of particle propagation in the Galaxy. Within a distance of a few parsec, diffusion regime is not valid and particles with energy below about 100 TeV must be influenced by the heliosphere and its elongated tail. The observation of a highly significant localized excess region of cosmic rays from the apparent direction of the downstream interstellar flow at 1–10 TeV energies might provide the first experimental evidence that the heliotail can affect the transport of energetic particles. In particular, TeV cosmic rays propagating through the heliotail interact with the 100–300 AU wide magnetic field polarity domains generated by the 11 yr cycles. Since the strength of non-linear convective processes is expected to be larger than viscous damping, the plasma in the heliotail is turbulent. Where magnetic field domains converge on each other due to solar wind gradient, stochastic magnetic reconnection likely occurs. Such processes may be efficient enough to re-accelerate a fraction of TeV particles as long as scattering processes are not strong. Therefore, the fractional excess of TeV cosmic rays from the narrow region toward the heliotail direction traces sightlines with the lowest smearing scattering effects, that can also explain the observation of a harder than average energy spectrum.

scholarly journals Limiting the shock acceleration of cosmic ray protons in the ICM

2020 ◽  
Vol 495 (1) ◽  
pp. L112-L117 ◽  
Author(s):  
D Wittor ◽  
F Vazza ◽  
D Ryu ◽  
H Kang
Keyword(s):  
Cosmic Rays ◽  
Galaxy Clusters ◽  
Large Scale ◽  
Cosmic Ray ◽  
Shock Acceleration ◽  
Diffusive Shock Acceleration ◽  
Magnetic Field Topology ◽  
Tracer Particles ◽  
Γ Rays ◽  
Massive Galaxy

ABSTRACT Observations of large-scale radio emissions prove the existence of shock accelerated cosmic ray electrons in galaxy clusters, while the lack of detected γ-rays limits the acceleration of cosmic ray protons in galaxy clusters. This challenges our understanding of how diffusive shock acceleration works. In this work, we couple the most updated recipes for shock acceleration in the intracluster medium to state-of-the-art magnetohydrodynamical simulations of massive galaxy clusters. Furthermore, we use passive tracer particles to follow the evolution of accelerated cosmic rays. We show that when the interplay between magnetic field topology and the feedback from accelerated cosmic rays is taken into account, the latest developments of particle acceleration theory give results that are compatible with observational constraints.

scholarly journals Shock acceleration efficiency in radio relics

2020 ◽  
Vol 634 ◽  
pp. A64 ◽  
Author(s):  
A. Botteon ◽  
G. Brunetti ◽  
D. Ryu ◽  
S. Roh
Keyword(s):  
Cosmic Rays ◽  
Galaxy Clusters ◽  
Electron Acceleration ◽  
Shock Acceleration ◽  
X Rays ◽  
Radio Luminosity ◽  
Diffusive Shock Acceleration ◽  
Astrophysical Shocks ◽  
Energy Dissipated ◽  
Relativistic Particles

Context. Radio relics in galaxy clusters are giant diffuse synchrotron sources powered in cluster outskirts by merger shocks. Although the relic–shock connection has been consolidated in recent years by a number of observations, the details of the mechanisms leading to the formation of relativistic particles in this environment are still not well understood. Aims. The diffusive shock acceleration (DSA) theory is a commonly adopted scenario to explain the origin of cosmic rays at astrophysical shocks, including those in radio relics in galaxy clusters. However, in a few specific cases it has been shown that the energy dissipated by cluster shocks is not enough to reproduce the luminosity of the relics via DSA of thermal particles. Studies based on samples of radio relics are required to further address this limitation of the mechanism. Methods. In this paper, we focus on ten well-studied radio relics with underlying shocks observed in the X-rays and calculate the electron acceleration efficiency of these shocks that is necessary to reproduce the observed radio luminosity of the relics. Results. We find that in general the standard DSA cannot explain the origin of the relics if electrons are accelerated from the thermal pool with an efficiency significantly smaller than 10%. Our results show that other mechanisms, such as shock re-acceleration of supra-thermal seed electrons or a modification of standard DSA, are required to explain the formation of radio relics.

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