Collisionless Shocks in Partly Ionized Plasma with Cosmic Rays: Microphysics of Non-thermal Components

Bykov, A. M.; Malkov, Mikhail; Raymond, J. C.; Krassilchtchikov, A. M.; Vladimirov, Andrey

doi:10.1007/s11214-013-9984-7

Cited by 33 publications

(27 citation statements)

References 139 publications

(221 reference statements)

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“…As a result, the shock does not have to decelerate to a velocity as low as when DSA is inefficient to achieve a downstream temperature at which the gas can cool down effectively through radiation. A similar result has also been obtained by Bykov et al (2013). This also means that when the shock became radiative, the shock was still strong enough to support NLDSA so that at that time P CR has already dominated the post-shock pressure to support the gas from collapsing drastically.…”

Section: Case Of Nldsa With Thermal Injectionsupporting

confidence: 81%

“…This can lead to a more highly ionized gas compared to the equilibrium values at v 120 sk < km s −1 . Also, f ion can change if nonlinear feedback of DSA to the shock structure is considered (Bykov et al 2013), and the formulae in Hollenbach & McKee (1989) must be modified; shock modification by the CR pressure results in an increase of the total compression ratio and decrease of the subshock compression ratio, which leads to a reduction of the post-shock temperature relative to the standard value for unmodified shocks. This hastens the transition of the shock to the radiative phase, and the ion fraction can start to increase due to photoionization at a higher shock velocity.…”

Section: Diffusion Coefficient and Momentum Breakmentioning

confidence: 99%

“…Moreover, these γ-rays that are concentrated in the GeV energy band possess a characteristic spectral shape that deviates from a simple power law with an exponential cutoff; rather, it points to the existence of a peculiar spectral break in the underlying proton distribution, typically at a few to a few tens of GeV with a softening of the spectral index by roughly one power from the lower to higher energy side of the break, the origin of which is still not clearly understood. Our current understanding and the major unknowns of the physics involved in particle acceleration and non-thermal emission at a radiative shock is covered in a review by Bykov et al (2013).…”

Section: Introductionmentioning

confidence: 99%

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MODELING BRIGHTγ-RAY AND RADIO EMISSION AT FAST CLOUD SHOCKS

Lee

Patnaude

Raymond

et al. 2015

ApJ

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Recent observations by the Large Area Telescope on board the Fermi satellite have revealed bright γ-ray emission from middle-aged supernova remnants (SNRs) inside our Galaxy. These remnants, which also possess bright nonthermal radio shells, are often found to be interacting directly with surrounding gas clouds. We explore the nonthermal emission mechanism at these dynamically evolved SNRs by constructing a hydrodynamical model. Two scenarios of particle acceleration, either a re-acceleration of Galactic cosmic rays or an efficient nonlinear diffusive shock acceleration (NLDSA) of particles injected from downstream, are considered. Using parameters inferred from observations, our models are contrasted with the observed spectra of SNR W44. For the re-acceleration case, we predict a significant enhancement of radio and GeV emission as the SNR undergoes a transition into the radiative phase. If sufficiently strong magnetic turbulence is present in the molecular cloud, the re-acceleration scenario can explain the observed broadband spectral properties. The NLDSA scenario also succeeds in explaining the γ-ray spectrum but fails to reproduce the radio spectral index. Efficient NLDSA also results in a significant post-shock non-thermal pressure that limits the compression during cooling and prevents the formation of a prominent dense shell. Some other interesting differences between the two models in hydrodynamical behavior and resulting spectral features are illustrated.

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Section: Case Of Nldsa With Thermal Injectionsupporting

confidence: 81%

Section: Diffusion Coefficient and Momentum Breakmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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MODELING BRIGHTγ-RAY AND RADIO EMISSION AT FAST CLOUD SHOCKS

Lee

Patnaude

Raymond

et al. 2015

ApJ

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“…In the case of shocks propagating through partially ionized plasmas charge-exchange particle collisions provide a return flux of highly super-thermal neutrals heating the upstream plasma reducing the fluid Mach number and the compression ratio in Balmer-type shocks of velocities below 3,000 km s −1 (see, e.g., Blasi et al 2012). The efficient CR acceleration may also modify the structure and the ultraviolet-optical-infrared emission spectra of MHD radiative shocks (see, e.g., Bykov et al 2013c).…”

Section: Particle Acceleration By Collisionless Shocksmentioning

confidence: 99%

Nonthermal particles and photons in starburst regions and superbubbles

Bykov

2014

Astron Astrophys Rev

118

102

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Starforming factories in galaxies produce compact clusters and loose associations of young massive stars. Fast radiation-driven winds and supernovae input their huge kinetic power into the interstellar medium in the form of highly supersonic and superalfvenic outflows. Apart from gas heating, collisionless relaxation of fast plasma outflows results in fluctuating magnetic fields and energetic particles. The energetic particles comprise a long-lived component which may contain a sizeable fraction of the kinetic energy released by the winds and supernova ejecta and thus modify the magnetohydrodynamic flows in the systems. We present a concise review of observational data and models of nonthermal emission from starburst galaxies, superbubbles, and compact clusters of massive stars. Efficient mechanisms of particle acceleration and amplification of fluctuating magnetic fields with a wide dynamical range in starburst regions are discussed. Sources of cosmic rays, neutrinos and multi-wavelength nonthermal emission associated with starburst regions including potential galactic "PeVatrons" are reviewed in the global galactic ecology context.

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“…The structure of the radiative shock depends on the line opacity which, for radiative SNR shocks, typically allows the escape of some optical and fine-structure infrared (IR) lines of abundant ions providing observational diagnostics of the shocks (see e.g., Raymond 1979;Hollenbach and McKee 1989;Gnat and Sternberg 2009;Bykov et al 2013a). …”

Section: Radiative Shocksmentioning

confidence: 99%

Supernova Remnants Interacting with Molecular Clouds: X-Ray and Gamma-Ray Signatures

et al. 2014

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The giant molecular clouds (MCs) found in the Milky Way and similar galaxies play a crucial role in the evolution of these systems. The supernova explosions that mark the death of massive stars in these regions often lead to interactions between the supernova remnants (SNRs) and the clouds. These interactions have a profound effect on our understanding of SNRs. Shocks in SNRs should be capable of accelerating particles to cosmic ray (CR) energies with efficiencies high enough to power Galactic CRs. X-ray and γ-ray studies have established the presence of relativistic electrons and protons in some SNRs and provided strong evidence for diffusive shock acceleration as the primary acceleration mechanism, including strongly amplified magnetic fields, temperature and ionization effects on the shock-heated plasmas, and modifications to the dynamical evolution of some systems. Because protons dominate the overall energetics of the CRs, it is crucial to understand this hadronic component even though electrons are much more efficient radiators and it can be difficult to identify the hadronic component. However, near MCs the densities are sufficiently high to allow the γ-ray emission to be dominated by protons. Thus, these interaction sites provide some of our best opportunities to constrain the overall energetics of these particle accelerators. Here we summarize some key properties of interactions between SNRs and MCs, with an emphasis on recent X-ray and γ-ray studies that are providing important constraints on our understanding of cosmic rays in our Galaxy.

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Collisionless Shocks in Partly Ionized Plasma with Cosmic Rays: Microphysics of Non-thermal Components

Cited by 33 publications

References 139 publications

MODELING BRIGHTγ-RAY AND RADIO EMISSION AT FAST CLOUD SHOCKS

MODELING BRIGHTγ-RAY AND RADIO EMISSION AT FAST CLOUD SHOCKS

Nonthermal particles and photons in starburst regions and superbubbles

Supernova Remnants Interacting with Molecular Clouds: X-Ray and Gamma-Ray Signatures

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