109 research outputs found
A Cosmic Ray Resolution to the Superbubble Energy-Crisis
Superbubbles (SBs) are amongst the greatest injectors of energy into the
Galaxy, and have been proposed to be the acceleration site of Galactic cosmic
rays. They are thought to be powered by the fast stellar winds and powerful
supernova explosions of massive stars in dense stellar clusters and
associations. Observations of the SB 'DEM L192' in the neighboring Large
Magellenic Cloud (LMC) galaxy show that it contains only about one-third the
energy injected by its constituent stars via fast stellar winds and supernovae.
It is not yet understood where the excess energy is going, thus, the so-called
'energy crisis'. We show here that it is very likely that a significant
fraction of the unaccounted for energy is being taken up in accelerating cosmic
rays, thus bolstering the argument for the SB origin of cosmic rays.Comment: Accepted for publication in ApJ
Monopole harmonics on
We find the spectra and eigenfunctions of both ordinary and supersymmetric
quantum-mechanical models describing the motion of a charged particle over the
manifold in the presence of a background monopole-like
gauge field. The states form degenerate multiplets and their wave
functions acquire a very simple form being expressed via homogeneous
coordinates. Their relationship to multidimensional orthogonal polynomials of a
special kind is discussed. By the well-known isomorphism between the twisted
Dolbeault and Dirac complexes, our construction also gives the eigenfunctions
and eigenvalues of the Dirac operator on complex projective spaces in a
monopole background.Comment: 42 pages, 3 figures, v2: minor corrections, references adde
Nonthermal particles and photons in starburst regions and superbubbles
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
Electron and Ion Acceleration in Relativistic Shocks with Applications to GRB Afterglows
We have modeled the simultaneous first-order Fermi shock acceleration of
protons, electrons, and helium nuclei by relativistic shocks. By parameterizing
the particle diffusion, our steady-state Monte Carlo simulation allows us to
follow particles from particle injection at nonthermal thermal energies to
above PeV energies, including the nonlinear smoothing of the shock structure
due to cosmic-ray (CR) backpressure. We observe the mass-to-charge (A/Z)
enhancement effect believed to occur in efficient Fermi acceleration in
non-relativistic shocks and we parameterize the transfer of ion energy to
electrons seen in particle-in-cell (PIC) simulations. For a given set of
environmental and model parameters, the Monte Carlo simulation determines the
absolute normalization of the particle distributions and the resulting
synchrotron, inverse-Compton, and pion-decay emission in a largely
self-consistent manner. The simulation is flexible and can be readily used with
a wide range of parameters typical of gamma-ray burst (GRB) afterglows. We
describe some preliminary results for photon emission from shocks of different
Lorentz factors and outline how the Monte Carlo simulation can be generalized
and coupled to hydrodynamic simulations of GRB blast waves. We assume Bohm
diffusion for simplicity but emphasize that the nonlinear effects we describe
stem mainly from an extended shock precursor where higher energy particles
diffuse further upstream. Quantitative differences will occur with different
diffusion models, particularly for the maximum CR energy and photon emission,
but these nonlinear effects should be qualitatively similar as long as the
scattering mean free path is an increasing function of momentum.Comment: Accepted for publication in MNRA
Spectra of magnetic fluctuations and relativistic particles produced by a nonresonant wave instability in supernova remnant shocks
We model strong forward shocks in young supernova remnants with efficient
particle acceleration where a nonresonant instability driven by the cosmic ray
current amplifies magnetic turbulence in the shock precursor. Particle
injection, magnetic field amplification (MFA) and the nonlinear feedback of
particles and fields on the bulk flow are derived consistently. The shock
structure depends critically on the efficiency of turbulence cascading. If
cascading is suppressed, MFA is strong, the shock precursor is stratified, and
the turbulence spectrum contains several discrete peaks. These peaks, as well
as the amount of MFA, should influence synchrotron X-rays, allowing
observational tests of cascading and other assumptions intrinsic to the
nonlinear model of nonresonant wave growth.Comment: 3 figures, 5 pages. Accepted for publication in ApJ
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