12,595 research outputs found
The Cosmic Ray - X-ray Connection: Effects of Nonlinear Shock Acceleration on Photon Production in SNRs
Cosmic-ray production in young supernova remnant (SNR) shocks is expected to
be efficient and strongly nonlinear. In nonlinear, diffusive shock
acceleration, compression ratios will be higher and the shocked temperature
lower than test-particle, Rankine-Hugoniot relations predict. Furthermore, the
heating of the gas to X-ray emitting temperatures is strongly coupled to the
acceleration of cosmic-ray electrons and ions, thus nonlinear processes which
modify the shock, influence the emission over the entire band from radio to
gamma-rays and may have a strong impact on X-ray line models. Here we apply an
algebraic model of nonlinear acceleration, combined with SNR evolution, to
model the radio and X-ray continuum of Kepler's SNR.Comment: 7 pages including 4 figures; to appear in ``The Acceleration and
Transport of Energetic Particles Observed in the Heliosphere,'' Proceedings
of the ACE-2000 Symposium held on January 5 - 8, 2000, Indian Springs, C
Nonlinear Particle Acceleration in Relativistic Shocks
Monte Carlo techniques are used to model nonlinear particle acceleration in
parallel collisionless shocks of various speeds, including mildly relativistic
ones. When the acceleration is efficient, the backreaction of accelerated
particles modifies the shock structure and causes the compression ratio, r, to
increase above test-particle values. Modified shocks with Lorentz factors less
than about 3 can have compression ratios considerably greater than 3 and the
momentum distribution of energetic particles no longer follows a power law
relation. These results may be important for the interpretation of gamma-ray
bursts if mildly relativistic internal and/or afterglow shocks play an
important role accelerating particles that produce the observed radiation. For
shock Lorentz factors greater than about 10, r approaches 3 and the so-called
`universal' test-particle result of N(E) proportional to E^{-2.3} is obtained
for sufficiently energetic particles. In all cases, the absolute normalization
of the particle distribution follows directly from our model assumptions and is
explicitly determined.Comment: Updated version, Astroparticle Physics, in press, 29 pages, 13
figure
Experimental stagnation point velocity gradients and heat transfer coefficients for a family of blunt bodies at Mach 8 and angles of attack
Stagnation pressure and heat transfer measurements of blunt axisymmetric bodie
Wind tunnel buffet load measuring technique
Indirect force measurement technique estimates unsteady forces acting on elastic model during wind tunnel tests. Measurement of forces is practically insensitive to errors in aeroelastic scaling between model and full-scale structure, simplifying design, fabrication and dynamic calibration
The Role of Diffusive Shock Acceleration on Nonequilibrium Ionization in Supernova Remnant Shocks II: Emitted Spectra
We present a grid of nonequilibrium ionization models for the X-ray spectra
from supernova remnants undergoing efficient diffusive shock acceleration. The
calculation follows the hydrodynamics of the blast wave as well as the
time-dependent ionization of the plasma behind the shock. The ionization state
is passed to a plasma emissivity code to compute the thermal X-ray emission,
which is combined with the emission from nonthermal synchrotron emission to
produce a self-consistent model for the thermal and nonthermal emission from
cosmic-ray dominated shocks. We show how plasma diagnostics such as the
G'-ratio of He-like ions, defined as the ratio of the sum of the
intercombination, forbidden, and satellite lines to the resonance line, can
vary with acceleration efficiency, and discuss how the thermal X-ray emission,
when the time-dependent ionization is not calculated self-consistently with the
hydrodynamics, can differ from the thermal X-ray emission from models which do
account for the hydrodynamics. Finally we compare the thermal X-ray emission
from models which show moderate acceleration (~ 35%) to the thermal X-ray
emission from test-particle models.Comment: 17 pages, 12 figures. accepted for publication in the Astrophysical
Journa
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