scholarly journals Particle acceleration and magnetic field amplification in massive young stellar object jets

2021 ◽  
Author(s):  
Anabella T Araudo ◽  
Marco Padovani ◽  
Alexandre Marcowith
Keyword(s):  
Magnetic Field ◽  
Cosmic Ray ◽  
Maximum Energy ◽  
Shock Acceleration ◽  
Relativistic Electrons ◽  
Diffusive Shock Acceleration ◽  
Field Amplification ◽  
Protostellar Jets ◽  
Γ Rays ◽  
The Magnetic Field

Abstract Synchrotron radio emission from non-relativistic jets powered by massive protostars has been reported, indicating the presence of relativistic electrons and magnetic fields of strength ∼0.3 −5 mG. We study diffusive shock acceleration and magnetic field amplification in protostellar jets with speeds between 300 and 1500 km s−1. We show that the magnetic field in the synchrotron emitter can be amplified by the non-resonant hybrid (Bell) instability excited by the cosmic-ray streaming. By combining the synchrotron data with basic theory of Bell instability we estimate the magnetic field in the synchrotron emitter and the maximum energy of protons. Protons can achieve maximum energies in the range 0.04 − 0.65 TeV and emit γ rays in their interaction with matter fields. We predict detectable levels of γ rays in IRAS 16547-5247 and IRAS 16848-4603. The γ ray flux can be significantly enhanced by the gas mixing due to Rayleigh-Taylor instability. The detection of this radiation by the Fermi satellite in the GeV domain and the forthcoming Cherenkov Telescope Array at higher energies may open a new window to study the formation of massive stars, as well as diffusive acceleration and magnetic field amplification in shocks with velocities of about 1000 km s−1.

scholarly journals Oblique Shocks in Extragalactic Jets

1990 ◽  
Vol 140 ◽  
pp. 437-437
Author(s):  
D. Fraix-Burnet
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Shock Front ◽  
Shock Acceleration ◽  
Relativistic Electrons ◽  
Optical Polarization ◽  
Diffusive Shock Acceleration ◽  
Extragalactic Jets ◽  
The Magnetic Field ◽  
Oblique Shocks

In the framework of the diffusive shock acceleration of relativistic electrons in extragalactic jets, we show that it is possible to derive the speed of the jet. For this purpose, we transform continuity relations through an oblique shock front into the reference frame of the observer. We apply these calculations to knot A of the M87 jet. Measuring the deviation of the fluid through the shock front from high-resolution radio maps and the deviation of the magnetic field from optical polarization maps (Fraix-Burnet et al., 1989), we derive speeds of about 0.01 c (Fraix-Burnet and Biermann, in preparation). The compression ratio is most probably 4 and the magnetic field is nearly parallel to the shock front both upstream and downstream.

scholarly journals New high-frequency radio observations of the Cygnus Loop supernova remnant with the Italian radio telescopes

2020 ◽  
Vol 500 (4) ◽  
pp. 5177-5194
Author(s):  
S Loru ◽  
A Pellizzoni ◽  
E Egron ◽  
A Ingallinera ◽  
G Morlino ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Frequency ◽  
Supernova Remnants ◽  
Cosmic Ray ◽  
Maximum Energy ◽  
Shock Acceleration ◽  
Radio Telescopes ◽  
Spectral Parameters ◽  
Cygnus Loop ◽  
Field Amplification

ABSTRACT Supernova remnants (SNRs) represent a powerful laboratory to study the cosmic ray acceleration processes at shocks, and their relation to the properties of the circumstellar medium. With the aim of studying the high-frequency radio emission and investigating the energy distribution of accelerated electrons and the magnetic field conditions, we performed single-dish observations of the large and complex Cygnus Loop SNR from 7.0–24.8 GHz with the Medicina and Sardinia Radio Telescopes, focusing on the northern filament (NGC 6992) and the southern shell. Both regions show a spectrum well fitted by a power-law function (S ∝ ν−α), with spectral index α = 0.45 ± 0.05 for NGC 6992 and α = 0.49 ± 0.01 for the southern shell and without any indication of a spectral break. The spectra are significantly flatter than the whole Cygnus Loop spectrum (α = 0.54 ± 0.01), suggesting a departure from the plain shock acceleration mechanisms, which for NGC 6992 could be related to the ongoing transition towards a radiative shock. We model the integrated spectrum of the whole SNR considering the evolution of the maximum energy and magnetic field amplification. Through the radio spectral parameters, we infer a magnetic field at the shock of 10 μG. This value is compatible with purely adiabatic compression of the interstellar magnetic field, suggesting that the amplification process is currently inefficient.

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 On the influence of supra-thermal particle acceleration on the morphology of low-Mach, high-β shocks

2020 ◽  
Vol 496 (3) ◽  
pp. 3198-3208
Author(s):  
Allard Jan van Marle
Keyword(s):  
Mach Number ◽  
Galaxy Cluster ◽  
Cosmic Ray ◽  
Shock Acceleration ◽  
Diffusive Shock Acceleration ◽  
Particle Injection ◽  
Particle In Cell ◽  
Injection Process ◽  
The Magnetic Field ◽  
High Computational Efficiency

ABSTRACT When two galaxy clusters encounter each other, the interaction results in a collisionless shock that is characterized by a low (1–4) sonic Mach number, and a high-Alfvénic Mach number. Our goal is to determine if, and to what extent, such shocks can accelerate particles to sufficient velocities that they can contribute to the cosmic ray spectrum. We combine two different computational methods, magnetohydrodynamics (MHD) and particle-in-cell (PIC) into a single code that allows us to take advantage of the high computational efficiency of MHD while maintaining the ability to model the behaviour of individual non-thermal particles. Using this method, we perform a series of simulations covering the expected parameter space of galaxy cluster collision shocks. Our results show that for shocks with a sonic Mach number below 2.25 no diffusive shock acceleration can take place because of a lack of instabilities in the magnetic field, whereas for shocks with a sonic Mach number $\ge \, 3$ the acceleration is efficient and can accelerate particles to relativistic speeds. In the regime between these two extremes, diffusive shock acceleration can occur but is relatively inefficient because of the time- and space-dependent nature of the instabilities. For those shocks that show efficient acceleration, the instabilities in the upstream gas increase to the point where they change the nature of the shock, which, in turn, will influence the particle injection process.

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 Nonlinear Diffusive Shock Acceleration with Magnetic Field Amplification

2006 ◽  
Vol 652 (2) ◽  
pp. 1246-1258 ◽  
Author(s):  
Andrey Vladimirov ◽  
Donald C. Ellison ◽  
Andrei Bykov
Keyword(s):  
Magnetic Field ◽  
Shock Acceleration ◽  
Diffusive Shock Acceleration ◽  
Field Amplification

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 Evolution and observational signatures of the cosmic ray electron spectrum in SN 1006

2020 ◽  
Vol 499 (2) ◽  
pp. 2785-2802
Author(s):  
Georg Winner ◽  
Christoph Pfrommer ◽  
Philipp Girichidis ◽  
Maria Werhahn ◽  
Matteo Pais
Keyword(s):  
Magnetic Field ◽  
Electron Spectrum ◽  
Supernova Remnants ◽  
Cosmic Ray ◽  
Electron Acceleration ◽  
Galactic Cosmic Rays ◽  
Shock Acceleration ◽  
X Rays ◽  
Γ Rays ◽  
Γ Ray

ABSTRACT Supernova remnants (SNRs) are believed to be the source of Galactic cosmic rays (CRs). SNR shocks accelerate CR protons and electrons which reveal key insights into the non-thermal physics by means of their synchrotron and γ-ray emission. The remnant SN 1006 is an ideal particle acceleration laboratory because it is observed across all electromagnetic wavelengths from radio to γ-rays. We perform 3D magnetohydrodynamics (MHD) simulations where we include CR protons and follow the CR electron spectrum. By matching the observed morphology and non-thermal spectrum of SN 1006 in radio, X-rays, and γ-rays, we gain new insight into CR electron acceleration and magnetic field amplification. (1) We show that a mixed leptonic–hadronic model is responsible for the γ-ray radiation: while leptonic inverse-Compton emission and hadronic pion-decay emission contribute equally at GeV energies observed by Fermi, TeV energies observed by imaging air Cherenkov telescopes are hadronically dominated. (2) We show that quasi-parallel acceleration (i.e. when the shock propagates at a narrow angle to the upstream magnetic field) is preferred for CR electrons and that the electron acceleration efficiency of radio-emitting GeV electrons at quasi-perpendicular shocks is suppressed at least by a factor ten. This precludes extrapolation of current 1D plasma particle-in-cell simulations of shock acceleration to realistic SNR conditions. (3) To match the radial emission profiles and the γ-ray spectrum, we require a volume-filling, turbulently amplified magnetic field and that the Bell-amplified magnetic field is damped in the immediate post-shock region. Our work connects microscale plasma physics simulations to the scale of SNRs.

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