Electromagnetic Processes In Strongly Magnetized Plasma

Context. We consider the radiative transfer problem in a planeparallel slab of thermal electrons in the presence of an ultrastrong magnetic field (B Bc ≈ 4.4 × 10 13 G). Under such conditions, the magnetic field behaves as a birefringent medium for the propagating photons, and the electromagnetic radiation is split into two polarization modes, ordinary and extraordinary, having different cross-sections. When the optical depth of the slab is large, the ordinary-mode photons are strongly Comptonized and the photon field is dominated by an isotropic component. Aims. The radiative transfer problem in strong magnetic fields presents many mathematical issues and analytical or numerical solutions can be obtained only under some given approximations. We investigate this problem both from the analytical and numerical point of view, providing a test of the previous analytical estimates and extending these results introducing numerical techniques. Methods. We consider here the case of low temperature blackbody photons propagating in a sub-relativistic temperature plasma, which allow us to deal with a semi Fokker-Planck approximation of the radiative transfer equation. The problem can be treated then with the variable separation method, and we use a numerical technique for finding solutions of the eigenvalue problem in the case of singular kernel of the space operator. The singularity of the space kernel is the result of the strong angular dependence of the Thomson-approximated electron cross-section in the presence of a strong magnetic field. Results. We report the numerical solution obtained for eigenvalues and eigenfunctions of the space operator, and the emerging Comptonization spectrum of the ordinary-mode photons for any eigenvalue of the space equation and for energies significantly less than the cyclotron energy, which is of the order of MeV for the intensity of the magnetic field here considered.

1999

Compton scattering of low-frequency radiation by an isotropic distribution of (i) mildly and (ii) ultra relativistic electrons is considered. It is shown that the ensemble-averaged differential cross-section in this case is noticeably different from the Rayleigh phase function. The scattering by an ensemble of ultra-relativistic electrons obeys the law p = 1−cos α, where α is the scattering angle; hence photons are preferentially scattered backwards. This contrasts the forward scattering behaviour in the Klein-Nishina regime. Analytical formulae describing first-order Klein-Nishina and finite-electron-energy corrections to the simple relation above are given for various energy distributions of electrons: monoenergetic, relativistic-Maxwellian, and power-law. A similar formula is also given for the mildly relativistic (with respect to the photon energy and electron temperature) corrections to the Rayleigh angular function. One of manifestations of the phenomenon under consideration is that hot plasma is more reflective with respect to external low-frequency radiation than cold one, which is important, in particular, for the photon exchange between cold accretion disks and hot atmospheres (coronae or ADAF flows) in the vicinity of relativistic compact objects; and for compact radiosources.

Physical Review D, 2016

Compton scattering of polarized radiation in a strong magnetic field is considered. The recipe for calculation of the scattering matrix elements, the differential and total cross sections based on quantum electrodynamic (QED) second order perturbation theory is presented for the case of arbitrary initial and final Landau level, electron momentum along the field and photon momentum. Photon polarization and electron spin state are taken into account. The correct dependence of natural Landau level width on the electron spin state is taken into account in general case of arbitrary initial photon momentum for the first time. A number of steps in calculations were simplified analytically making the presented recipe easy-to-use. The redistribution functions over the photon energy, momentum and polarization states are presented and discussed. The paper generalizes already known results and offers a basis for accurate calculation of radiation transfer in strong B-field, for example, in strongly magnetized neutron stars.

Physical Review D, 2012

We derive the relativistic kinetic equation for Compton scattering of polarized radiation in strong magnetic field using the Bogolyubov method. The induced scattering and the Pauli exclusion principle are taken into account. The electron polarization is also considered in the general form of the kinetic equation. The special forms of the equation for the cases of the non-polarized electrons, the rarefied electron gas and the two polarization mode description of radiation are found. The derived equations are valid for any photon and electron energies and the magnetic field strength below about 10 16 G. These equations provide the basis for formulation of the equation for polarized radiation transport in atmospheres and magnetospheres of strongly magnetized neutron stars.

Physical Review D, 2001

We evaluate the three-photon vertex functions at order B and B 2 in a weak constant magnetic field at finite temperature and density with on shell external lines. Their application to the study of the photon splitting process leads to consider high energy photons whose dispersion relations are not changed significantly by the plasma effects. The absorption coefficient is computed and compared with the perturbative vacuum result. For the values of temperature and density of some astrophysical objects with a weak magnetic field, the matter effects are negligible.

The Astrophysical Journal, 2021

Accurate radiative transfer coefficients (emissivities, absorptivities, and rotativities) are needed for modeling radiation from relativistically hot, magnetized plasmas such as those found in Event Horizon Telescope sources. Here we review, update, and correct earlier work on radiative transfer coefficients. We also describe an improved method for numerically evaluating rotativities and provide convenient fitting formulae for the relativistic κ distribution of electron energies. Here α S and ρ S are absorption and Faraday mixing coefficients, respectively, in the Stokes basis. We use a Cartesian coordinate system in the calculation of the transfer coefficients. We setẑ parallel to the magnetic field B. The observer angle θ is the angle between B and the photon wavevector k which we choose to lie in the x − z plane. Note that we have chosen a coordinate system (in the plasma rest frame) such that all Stokes U coefficients are zero.

Monthly Notices of the Royal Astronomical Society, 2016

We find the forms of the transfer equations for polarized cyclotron radiation in the atmospheres of compact stars, which are simple enough to allow practical implementation and still preserve all important physical effects. We take into account a frequency redistribution of radiation within the cyclotron line as well as the relativistic and quantum-electrodynamic effects. Our analysis is valid for the magnetic fields up to 10 13 G and for temperatures well below 500 keV. We present and compare two forms of the radiation transfer equations. The first form, for the intensities of ordinary and extraordinary modes, is applicable for the compact stars with a moderate magnetic field strength up to 10 11 G for typical neutron star and up to 10 9 G for magnetic white dwarfs. The second form, for the Stokes parameters, is more complex, but applicable even if a linear mode coupling takes place somewhere in the scattering-dominated atmosphere. Analysing dispersion properties of a magnetized plasma in the latter case, we describe a range of parameters where the linear mode coupling is possible and essential.

Physical Review E, 2020

The propagation of a relativistic electron-positron beam in a magnetized electron-ion plasma is studied, focusing on the polarization of the radiation generated in this case. Special emphasis is laid on investigating the polarization of the generated radiation for a range of beam-plasma parameters, transverse and longitudinal beam sizes, and the external magnetic fields. Our results not only help in understanding the high degrees of circular polarization observed in gamma-rays bursts but they also help in distinguishing the different modes associated with the filamentation dynamics of the pair-beam in laboratory astrophysics experiments.

2021

Emission process of a charged particle propagating in a medium with a curved magnetic field is considered. This mechanism combines features of conventional Cherenkov and curvature emission. Thus, presence of a medium with the index of refraction larger than the unity is essential for the emission. In the present paper the generation of high frequency radiation by the mentioned mechanism is considered. The generated waves are vacuum-like electromagnetic waves and may leave the medium directly. Consequently, this emission mechanism may be important for the problem of pulsar X-ray and gamma-ray emission generation. Subject headings: pulsars: general — radiation processes: nonthermal

Australian Journal of Physics, 1992

Approximate analytic expressions are derived for the linear response 4-tensor of a strongly magnestised, mildly relativistic electron plasma. The results are obtained within the framework of quantum plasma dynamics, thus the response contains relativistic and quantum effects that are essential in a super-strong magnetic field. The response is obtained in terms of relativistic plasma dispersion functions known as Shkarofsky functions. These functions allow the wave properties of the plasma to be studied without resorting to complicated numerical schemes. The response derived is valid for radiation with frequency up to about the cyclotron frequency and is of use in the theory of spectra formation in X-ray pulsars. In addition, a simple graphical technique is introduced that allows one to visually locate the roots of the resonant denominator occurring in the response, as well as determine the conditions under which both roots are valid and contribute to absorption.

Physics of Plasmas, 2007

This paper presents some aspects of interaction of superstrong high-frequency electromagnetic waves with strongly magnetized plasmas. The case in which the photon-photon interaction dominates the photon-plasma particle interaction is considered. Strictly speaking, the photon and photon bunch interaction leads to the self-modulation of the photon gas. Assuming that the density of the plasma does not change, the dispersion relation, which includes relativistic self-modulation, is investigated. The existence of longitudinal photons in a strong magnetic field has the well-known Bogoliubov-type energy spectrum. The stability of the photon flow is investigated and an expression for Landau damping of the photons is obtained. Finally, it has been shown that the interaction of even a very strong electromagnetic radiation with a plasma does not always lead to instability, but causes only a change in plasma properties, whereby the plasma remains stable.

Universe

Both the lack of observation of ultra-high energy (UHE) photons and the limitations of the state-of-the-art methodology being applied for their identification motivate studies on alternative approaches to the relevant simulations and the related observational strategies. One such new approach is proposed in this report and it concerns new observables allowing indirect identification of UHE photons through cosmic ray phenomena composed of many spatially correlated extensive air showers or primary cosmic rays observed at one time. The study is based on simulations of interactions of UHE photons with the magnetic field of the Sun using the PRESHOWER program with some essential modifications. One of the expected results of such interactions is a generation of cosmic ray ensembles (CREs) in the form of very thin and very elongated cascades of secondary photons of energies spanning the whole cosmic ray energy spectrum. Upon entering the Earth’s atmosphere, these cascades or their parts ma...

Astronomy & Astrophysics - ASTRON ASTROPHYS, 2000

Electrons accelerated at the polar cap of a pulsar lose energy by interactions with the thermal photospheric radiation. Using Michel's acceleration model (\cite{Mic74}) we present an analytical treatement of these braking processes taking into account curvature radiation as well as resonant and non-resonant inverse Compton scattering and the distribution of the thermal photons originating from the polar cap. Results are obtained for a wide range of pulsar parameters. It turns out that for photospheric temperatures below kT =~ 100 eV and polar magnetic fields below B =~ 1012.5 Gauss braking by inverse Compton scattering has negligible influence on the end energy of the electrons around the polar axes. For magnetic field strength between 1012.5 and 1013.5 Gauss the energy loss is significant but depends on the pulsar rotation period. In the case of very high temperatures such as kT = 1 keV the energy loss is dramatic within a wide range of magnetic field strengths. Millisecond pu...

Monthly Notices of the Royal Astronomical Society, 2003

We present simple analytical formulae for the emission spectrum and total power of a special kind of resonant inverse Compton scattering (RICS) of a relativistic electron in an intense magnetic field. In contrast with the available formulae system, we obtain a markedly simplified one based on the semiclassical quantum theory, which is more understandable for people who are unfamiliar with quantum electrodynamics. We show that the RICS process, under an appropriate 'accommodation condition' derived in this paper, is predominantly much more efficient than the coexistent ordinary inverse Compton scattering, and produces highly beamed high-frequency radiation with moderately good monochromaticity. Our formulae are simple to use-thus offering a lucid physical intuition for the theory-and may find wide applications in hard X-ray and gamma-ray astrophysics.

Monthly Notices of the Royal Astronomical Society, 2006