12 research outputs found
Compton Scattering in Static and Moving Media. II. System-Frame Solutions for Spherically Symmetric Flows
I study the formation of Comptonization spectra in spherically symmetric,
fast moving media in a flat spacetime. I analyze the mathematical character of
the moments of the transfer equation in the system-frame and describe a
numerical method that provides fast solutions of the time-independent radiative
transfer problem that are accurate in both the diffusion and free-streaming
regimes. I show that even if the flows are mildly relativistic (V~0.1, where V
is the electron bulk velocity in units of the speed of light), terms that are
second-order in V alter the emerging spectrum both quantitatively and
qualitatively. In particular, terms that are second-order in V produce
power-law spectral tails, which are the dominant feature at high energies, and
therefore cannot be neglected. I further show that photons from a static source
are upscattered by the bulk motion of the medium even if the velocity field
does not converge. Finally, I discuss these results in the context of radial
accretion onto and outflows from compact objects.Comment: 28 pages, 9 figures; minor changes, to appear in the Astrophysical
Journa
Compton Scattering by Static and Moving Media I. The Transfer Equation and Its Moments
Compton scattering of photons by nonrelativistic particles is thought to play
an important role in forming the radiation spectrum of many astrophysical
systems. Here we derive the time-dependent photon kinetic equation that
describes spontaneous and induced Compton scattering as well as absorption and
emission by static and moving media, the corresponding radiative transfer
equation, and their zeroth and first moments, in both the system frame and in
the frame comoving with the medium. We show that it is necessary to use the
correct relativistic differential scattering cross section in order to obtain a
photon kinetic equation that is correct to first order in epsilon/m_e, T_e/m_e,
and V, where epsilon is the photon energy, T_e and m_e are the electron
temperature and rest mass, and V is the electron bulk velocity in units of the
speed of light. We also demonstrate that the terms in the radiative transfer
equation that are second-order in V usually should be retained, because if the
radiation energy density is sufficiently large compared to the radiation flux,
the effects of bulk Comptonization described by the terms that are second-order
in V are at least as important as the effects described by the terms that are
first-order in V, even when V is small. Our equations are valid for systems of
arbitrary optical depth and can therefore be used in both the free-streaming
and the diffusion regimes. We demonstrate that Comptonization by the electron
bulk motion occurs whether or not the radiation field is isotropic or the bulk
flow converges and that it is more important than thermal Comptonization if V^2
> 3 T_e/m_e.Comment: 31 pages, accepted for publication in The Astrophysical Journa
A high-frequency study of the Sunyaev-Zel'dovich effect morphology in galaxy clusters
High-frequency, high-resolution imaging of the Sunyaev-Zel'dovich (SZ) effect
is an important technique to study the complex structures of the atmospheres of
merging galaxy clusters. Such observations are sensitive to the details of the
electron spectrum. We show that the morphology of the SZ intensity maps in
simulated galaxy clusters observed at 345 GHz, 600 GHz, and 857 GHz are
significantly different because of SZ relativistic corrections. These
differences can be revealed by high-resolution imaging instruments.
We calculate relativistically corrected SZ intensity maps of a simulated,
massive, merging galaxy cluster and of the massive, merging clusters 1E0657-558
(the Bullet Cluster) and Abell 2219. The morphologies of the SZ intensity maps
are remarkably different between 345 GHz and 857 GHz for each merging cluster.
We show that high-resolution imaging observations of the SZ intensity maps at
these frequencies, obtainable with the LABOCA and HERSCHEL-SPIRE instruments,
allow to fully exploit the astrophysical relevance of the predicted SZ
morphological effect.Comment: 9 pages, 14 figures, accepted for publication in MNRA
Relativistic Kinetic Equation for Induced Compton Scattering of Polarized Radiation
The relativistic kinetic equations describing time evolution and space
dependence of the density matrices of polarized photons and electrons
interacting via Compton scattering are deduced from the quantum Liouville
equation. The induced scattering and exclusion principle are taken into
account. The Bogoliubov method is used in the frame of quantum electrodynamics.
The equation for polarized radiation scattered by unpolarized electrons is
considered as a particular case and is reformulated in terms of the Stokes
parameters. The expressions for the scattering amplitudes and cross-sections
are derived simultaneously.Comment: 19 pages; Astronomy & Astrophysics, in pres
Non-LTE Models and Theoretical Spectra of Accretion Disks in Active Galactic Nuclei. IV. Effects of Compton Scattering and Metal Opacities
We extend our models of the vertical structure and emergent radiation field
of accretion disks around supermassive black holes described in previous papers
of this series. Our models now include both a self-consistent treatment of
Compton scattering and the effects of continuum opacities of the most important
metal species (C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni). With these new effects
incorporated, we compute the predicted spectrum from black holes accreting at
nearly the Eddington luminosity (L/L_Edd = 0.3) and central masses of 10^6,
10^7, and 10^8 M_sun. We also consider two values of the Shakura-Sunyaev alpha
parameter, 0.1 and 0.01. Although it has little effect when M > 10^8 M_sun,
Comptonization grows in importance as the central mass decreases and the
central temperature rises. It generally produces an increase in temperature
with height in the uppermost layers of hot atmospheres. Compared to models with
coherent electron scattering, Comptonized models have enhanced EUV/soft X-ray
emission, but they also have a more sharply declining spectrum at very high
frequencies. Comptonization also smears the hydrogen and the He II Lyman edges.
The effects of metals on the overall spectral energy distribution are smaller
than the effects of Comptonization for these parameters. Compared to pure
hydrogen-helium models, models with metal continuum opacities have reduced flux
in the high frequency tail, except at the highest frequencies, where the flux
is very low. Metal photoionization edges are not present in the overall
disk-integrated model spectra. In addition to our new grid of models, we also
present a simple analytic prescription for the vertical temperature structure
of the disk in the presence of Comptonization, and show under what conditions a
hot outer layer (a corona) is formed.Comment: 22 pages, Latex. 19 figures. Uses corrected version of emulateapj.sty
and apjfonts.sty (included). Accepted for publication in Ap
Diffusion compton dans un gaz d'électrons Maxwelliens
We develop the relativistic Boltzmann equation for photon transport with non coherent scattering in the form of a Fokker-Planck equation usable for thermal photons. We give an expression of the corresponding equation in the spherical harmonies approximation. Finally, we establish formulae for energy exchange between radiation and matter.On développe l'équation de Boltzmann relativiste applicable au transfert des photons avec diffusion non cohérente sous forme d'une équation de Fokker-Planck utilisable pour les photons thermiques. On donne l'expression des équations de transfert correspondant à l'approximation des harmoniques sphériques. Enfin, on établit diverses formules applicables à l'échange d'énergie matière-rayonnement