Source models with electron diffusion

Gratton, L.

doi:10.1007/bf00643094

Cited by 28 publications

(27 citation statements)

References 9 publications

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“…Gratton (1972) assumed a point source which makes r = 0 a singularity in N tot (ν, r). We performed integrations along the line of sight starting at a cutoff radius, but this did not affect the larger scale results.…”

Section: Pure Diffusion Modelmentioning

confidence: 99%

“…In the early diffusion models for the Crab Nebula (Gratton 1972;Wilson 1972;Weinberg & Silk 1976), the diffusion coefficient was assumed to be constant with energy, and that is the assumption that we make in most of our modeling. Weinberg & Silk (1976) argued for a constant coefficient based on the fact that the diffusion length is likely to be related to the size of magnetic filaments and is much larger than the gyroradius.…”

Section: Outer Structure Of Young Pulsar Nebulaementioning

confidence: 99%

“…Although observations of the Crab clearly show evidence for a relativistic wind close to the pulsar, a pure diffusion model illustrates one limiting case of the expected particle transport. We used the pure diffusion model developed by Gratton (1972) to fit the spectral index distribution of the Crab from radio to optical, and 3C 58 and G21.5-0.9 in X-rays. We also used the model to calculate the half-light radius of the Crab from radio to X-rays.…”

Section: Outer Structure Of Young Pulsar Nebulaementioning

confidence: 99%

“…The radial emission profiles were first modeled as a central particle source with diffusion into the larger nebula (Gratton 1972;Wilson 1972). Rees & Gunn (1974) specified a termination shock in the pulsar wind as the source of the particle acceleration and viewed the outer part of the nebula as a place where the pulsar magnetic field winds up and the flow decelerates.…”

Section: Introductionmentioning

confidence: 99%

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Particle Transport in Young Pulsar Wind Nebulae

Tang

Chevalier

2012

ApJ

103

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The model for pulsar wind nebulae (PWNe) as a result of the magnetohydrodynamic (MHD) downstream flow from a shocked, relativistic pulsar wind has been successful in reproducing many features of the nebulae observed close to central pulsars. However, observations of well-studied young nebulae like the Crab Nebula, 3C 58, and G21.5-0.9 do not show the toroidal magnetic field on a larger scale that might be expected in the MHD flow model; in addition, the radial variation of spectral index due to synchrotron losses is smoother than expected in the MHD flow model. We find that pure diffusion models can reproduce the basic data on nebular size and spectral index variation for the Crab, 3C 58, and G21.5-0.9. Most of our models use an energy-independent diffusion coefficient; power-law variations of the coefficient with energy are degenerate with variation in the input particle energy distribution index in the steady state, transmitting boundary case. Energy-dependent diffusion is a possible reason for the smaller diffusion coefficient inferred for the Crab. Monte Carlo simulations of the particle transport allowing for advection and diffusion of particles suggest that diffusion dominates over much of the total nebular volume of the Crab. Advection dominates close to the pulsar and is likely to play a role in the X-ray half-light radius. The source of diffusion and mixing of particles is uncertain, but may be related to the Rayleigh-Taylor instability at the outer boundary of a young PWN or to instabilities in the toroidal magnetic field structure.

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Section: Pure Diffusion Modelmentioning

confidence: 99%

Section: Outer Structure Of Young Pulsar Nebulaementioning

confidence: 99%

Section: Outer Structure Of Young Pulsar Nebulaementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Particle Transport in Young Pulsar Wind Nebulae

Tang

Chevalier

2012

ApJ

103

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“…We can derive the Green function of Eq. (6) for the injection time t k (see Syrovatskii 1959;Gratton 1972) and then sum over injections. The equation for the Green function is…”

Section: Spatial and Energy Distributions Of Subrelativistic Protons mentioning

confidence: 99%

Nuclear interaction gamma-ray lines from the Galactic center region

Dogiel

Tatischeff

Cheng

et al. 2009

A&A

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Aims. The accretion of stars onto the central supermassive black hole at the center of the Milky Way is predicted to generate large fluxes of subrelativistic ions in the Galactic center region. We analyze the intensity, shape, and spatial distribution of de-excitation gamma-ray lines produced by nuclear interactions of these energetic particles with the ambient medium. Methods. We first estimated the amount and mean kinetic energy of particles released from the central black hole during star disruption. We then calculated the energy and spatial distributions of these particles in the Galactic center region from a kinetic equation. These particle distributions were then used to derive the characteristics of the main nuclear interaction gamma-ray lines. Results. Because the time period of star capture by the supermassive black hole is expected to be shorter than the lifetime of the ejected fast particles against Coulomb losses, the gamma-ray emission is predicted to be stationary. We find that the nuclear deexcitation lines should be emitted from a region with a maximum 5 • angular radius. The total gamma-ray line flux below 8 MeV is calculated to be ∼10 −4 photons cm −2 s −1 . The most promising lines for detection are those at 4.44 and ∼6.2 MeV, with a predicted flux in each line of ∼10 −5 photons cm −2 s −1 . Unfortunately, it is unlikely that this emission can be detected with the INTEGRAL observatory. But the predicted line intensities appear to be within reach of future gamma-ray space instruments. A future detection of de-excitation gamma-ray lines from the Galactic center region would provide unique information on the high-energy processes induced by the central supermassive black hole and the physical conditions of the emitting region.

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Plerionic Supernova Remnants

Bandiera

1990

Physical Processes in Hot Cosmic Plasmas

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Source models with electron diffusion

Cited by 28 publications

References 9 publications

Particle Transport in Young Pulsar Wind Nebulae

Particle Transport in Young Pulsar Wind Nebulae

Nuclear interaction gamma-ray lines from the Galactic center region

Plerionic Supernova Remnants

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