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.

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 Constraining the coherence scale of the interstellar magnetic field using TeV gamma-ray observations of supernova remnants

2020 ◽  
Vol 496 (2) ◽  
pp. 2448-2461 ◽  
Author(s):  
Matteo Pais ◽  
Christoph Pfrommer ◽  
Kristian Ehlert ◽  
Maria Werhahn ◽  
Georg Winner
Keyword(s):  
Magnetic Field ◽  
Interstellar Medium ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Galactic Cosmic Rays ◽  
Shock Acceleration ◽  
Interstellar Gas ◽  
Narrow Angle ◽  
Magnetohydrodynamic Simulations ◽  
Tev Gamma Rays

ABSTRACT Galactic cosmic rays (CRs) are believed to be accelerated at supernova remnant (SNR) shocks. In the hadronic scenario, the TeV gamma-ray emission from SNRs originates from decaying pions that are produced in collisions of the interstellar gas and CRs. Using CR-magnetohydrodynamic simulations, we show that magnetic obliquity-dependent shock acceleration is able to reproduce the observed TeV gamma-ray morphology of SNRs such as Vela Jr and SN1006 solely by varying the magnetic morphology. This implies that gamma-ray bright regions result from quasi-parallel shocks (i.e. when the shock propagates at a narrow angle to the upstream magnetic field), which are known to efficiently accelerate CR protons, and that gamma-ray dark regions point to quasi-perpendicular shock configurations. Comparison of the simulated gamma-ray morphology to observations allows us to constrain the magnetic coherence scale λB around Vela Jr and SN1006 to $\lambda _B \simeq 13_{-4.3}^{+13}$ pc and $\lambda _B \gt 200_{-40}^{+50}$ pc, respectively, where the ambient magnetic field of SN1006 is consistent with being largely homogeneous. We find consistent pure hadronic and mixed hadronic-leptonic models that both reproduce the multifrequency spectra from the radio to TeV gamma-rays and match the observed gamma-ray morphology. Finally, to capture the propagation of an SNR shock in a clumpy interstellar medium, we study the interaction of a shock with a dense cloud with numerical simulations and analytics. We construct an analytical gamma-ray model for a core collapse SNR propagating through a structured interstellar medium, and show that the gamma-ray luminosity is only biased by 30 per cent for realistic parameters.

scholarly journals GALACTIC AND EXTRAGALACTIC SUPERNOVA REMNANTS AS SITES OF PARTICLE ACCELERATION

2013 ◽  
Vol 53 (A) ◽  
pp. 612-616
Author(s):  
Manami Sasaki
Keyword(s):  
Particle Acceleration ◽  
Supernova Remnants ◽  
Supernova Remnant ◽  
Strong Shock ◽  
Cosmic Ray ◽  
Galactic Cosmic Rays ◽  
X Rays ◽  
Basic Physics ◽  
Nearby Galaxies ◽  
Radiation Processes

Supernova remnants, owing to their strong shock waves, are likely sources of Galactic cosmic rays. Studies of supernova remnants in X-rays and gamma rays provide us with new insights into the acceleration of particles to high energies. This paper reviews the basic physics of supernova remnant shocks and associated particle acceleration and radiation processes. In addition, the study of supernova remnant populations in nearby galaxies and the implications for Galactic cosmic ray distribution are discussed.

scholarly journals Gamma-rays from reaccelerated particles at supernova remnant shocks

2019 ◽  
Vol 489 (1) ◽  
pp. 108-115 ◽  
Author(s):  
P Cristofari ◽  
P Blasi
Keyword(s):  
Gamma Rays ◽  
Supernova Remnants ◽  
Large Scale ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
Shock Acceleration ◽  
X Rays ◽  
Diffusive Shock Acceleration ◽  
Particle In Cell ◽  
Large Scale Magnetic Field

ABSTRACT Diffusive shock acceleration is considered as the main mechanism for particle energization in supernova remnants, as well as in other classes of sources. The existence of some remnants that show a bilateral morphology in the X-rays and gamma-rays suggests that this process occurs with an efficiency that depends upon the inclination angle between the shock normal and the large-scale magnetic field in which the shock propagates. This interpretation is additionally supported by recent particle-in-cell simulations that show how ions are not injected if the shock is more oblique than ∼45°. These shocks provide an excellent test bench for the process of reacceleration at the same shock: non-thermal seed particles that are reached by the shock front are automatically injected and accelerated. This process was recently discussed as a possible reason for some anomalous behaviour of the spectra of secondary cosmic ray nuclei. Here, we discuss how gamma-ray observations of selected supernova remnants can provide us with precious information about this process and lead us to a better assessment of particle diffusive shock reacceleration for other observables in cosmic ray physics.

scholarly journals The absolute energies of the groups in magnetic β-ray spectra

1924 ◽  
Vol 105 (729) ◽  
pp. 60-69 ◽  
Keyword(s):  
Magnetic Field ◽  
Wave Length ◽  
X Rays ◽  
Homogeneous Groups ◽  
Absorption Energy ◽  
Length Measurements ◽  
Γ Rays ◽  
Γ Ray ◽  
The Absolute ◽  
The Difference

Most β-ray bodies emit several homogeneous groups of β-rays, and the energies of the electrons forming these groups may be found from the deflection they suffer in a magnetic field. Various experiments have shown that these groups are due to the conversion, according to the quantum relation, of γ-rays in the different electronic levels of the atom. In fact, the energy of any group is of the form E 1 = hv — (absorption energy of level). Two β-ray groups due to the conversion of a γ-ray of definite frequency in the K and L levels of the atom will differ in energy by the difference in energy between the K and L absorption energies. Both in testing this equation, and in using it to deduce frequencies of the γ-rays, it is necessary to compare energies of β-rays determined in terms of a magnetic field, with absorption energies deduced from wave-length measurements of X-rays. It is thus important to obtain values of the absolute β-ray energies as accurate as possible. The most accurate previous values were those of Rutherford and Robinson.

scholarly journals Stochastic re-acceleration and magnetic-field damping in Tycho’s supernova remnant

2020 ◽  
Vol 639 ◽  
pp. A124
Author(s):  
A. Wilhelm ◽  
I. Telezhinsky ◽  
V. V. Dwarkadas ◽  
M. Pohl
Keyword(s):  
Magnetic Field ◽  
Supernova Remnant ◽  
Cosmic Ray ◽  
Shock Acceleration ◽  
Acceleration Of Particles ◽  
X Rays ◽  
Stochastic Acceleration ◽  
Broadband Spectrum ◽  
Background Magnetic Field ◽  
Particle Spectra

Context. Tycho’s supernova remnant (SNR) is associated with the historical supernova (SN) event SN 1572 of Type Ia. The explosion occurred in a relatively clean environment, and was visually observed, providing an age estimate. This SNR therefore represents an ideal astrophysical test-bed for the study of cosmic-ray acceleration and related phenomena. A number of studies suggest that shock acceleration with particle feedback and very efficient magnetic-field amplification combined with Alfvénic drift are needed to explain the rather soft radio spectrum and the narrow rims observed in X-rays. Aims. We show that the broadband spectrum of Tycho’s SNR can alternatively be well explained when accounting for stochastic acceleration as a secondary process. The re-acceleration of particles in the turbulent region immediately downstream of the shock should be efficient enough to impact particle spectra over several decades in energy. The so-called Alfvénic drift and particle feedback on the shock structure are not required in this scenario. Additionally, we investigate whether synchrotron losses or magnetic-field damping play a more profound role in the formation of the non-thermal filaments. Methods. We solved the full particle transport equation in test-particle mode using hydrodynamic simulations of the SNR plasma flow. The background magnetic field was either computed from the induction equation or follows analytic profiles, depending on the model considered. Fast-mode waves in the downstream region provide the diffusion of particles in momentum space. Results. We show that the broadband spectrum of Tycho can be well explained if magnetic-field damping and stochastic re-acceleration of particles are taken into account. Although not as efficient as standard diffusive shock acceleration, stochastic acceleration leaves its imprint on the particle spectra, which is especially notable in the emission at radio wavelengths. We find a lower limit for the post-shock magnetic-field strength ∼330 μG, implying efficient amplification even for the magnetic-field damping scenario. Magnetic-field damping is necessary for the formation of the filaments in the radio range, while the X-ray filaments are shaped by both the synchrotron losses and magnetic-field damping.

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 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 Steep Cosmic-Ray Spectra with Revised Diffusive Shock Acceleration

2021 ◽  
Vol 922 (1) ◽  
pp. 1
Author(s):  
Rebecca Diesing ◽  
Damiano Caprioli
Keyword(s):  
Cosmic Rays ◽  
Supernova Remnants ◽  
Cosmic Ray ◽  
Galactic Cosmic Rays ◽  
Shock Acceleration ◽  
Analytic Model ◽  
Diffusive Shock Acceleration ◽  
Energy Distributions ◽  
Magnetic Structures ◽  
Wide Range

Abstract Galactic cosmic rays (CRs) are accelerated at the forward shocks of supernova remnants (SNRs) via diffusive shock acceleration (DSA), an efficient acceleration mechanism that predicts power-law energy distributions of CRs. However, observations of nonthermal SNR emission imply CR energy distributions that are generally steeper than E −2, the standard DSA prediction. Recent results from kinetic hybrid simulations suggest that such steep spectra may arise from the drift of magnetic structures with respect to the thermal plasma downstream of the shock. Using a semi-analytic model of nonlinear DSA, we investigate the implications that these results have on the phenomenology of a wide range of SNRs. By accounting for the motion of magnetic structures in the downstream, we produce CR energy distributions that are substantially steeper than E −2 and consistent with observations. Our formalism reproduces both modestly steep spectra of Galactic SNRs (∝E −2.2) and the very steep spectra of young radio supernovae (∝E −3).

scholarly journals X-ray Synchrotron Polarization from Turbulent Plasmas in Supernova Remnants

2017 ◽  
Vol 12 (S331) ◽  
pp. 242-247
Author(s):  
Matthew G. Baring
Keyword(s):  
Supernova Remnants ◽  
Active Regions ◽  
Cosmic Ray ◽  
Polarization Degree ◽  
Shock Acceleration ◽  
Field Energy ◽  
X Rays ◽  
Mhd Turbulence ◽  
X Ray ◽  
Turbulent Field

AbstractAs supernova remnants (SNRs) age, they become efficient cosmic ray accelerators at their outer shell shocks. The current paradigm for shock acceleration theory favors turbulent field environs in the proximity of these shocks, turbulence driven by current instabilities involving energetic ions. With the imminent prospect of dedicated X-ray polarimeters becoming a reality, the possibility looms of probing turbulence on scales that couple to the super-TeV electrons that emit X-rays. This paper presents model X-ray polarization signatures from energetic electrons moving in simulated MHD turbulence of varying levels of “chaos.” The emission volumes are finite slabs that represent the active regions of young SNR shells. We find that the turbulent field energy must be quite limited relative to that of the total field in order for the X-ray polarization degree to be as strong as the radio measures obtained in some remnants. Results presented are pertinent to the planned IXPE and XIPE polarimeters.

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