Pulsar Plasma Research Articles

The effect of synchrotron absorption on the observed radio luminosities of pulsars

Propagation of radio waves through the flow of an ultrarelativistic magnetized plasma of pulsar magnetospheres is considered. It is known that, for the parameters typical of pulsar plasma, cyclotron absorption of radio emission is efficient and the absorbing particles easily acquire relativistic gyration. The character of synchrotron absorption, i.e. absorption by relativistically gyrating particles, can differ from that known for cyclotron absorption. It is shown that the particle pitch angles rapidly become comparable to the angle of incidence of the resonant radiation in the laboratory frame, ψ ∼ θ. Further, synchrotron absorption occurs in the regime θ - ψ << θ. The resonant frequency decreases with distance because of the magnetic field strength decrease. It is found that only the highest frequencies, ≥10 GHz, suffer absorption by the particles with ψ<< θ, whereas radiation over the remaining part of the radio frequency range is subject to synchrotron absorption in the regime θ - ψ << θ. It is the latter process that can affect the observed radio luminosities of pulsars. The optical depth to the synchrotron absorption in the limit θ - ψ « θ appears to be much less than that previously known for the limit ψ « θ. For long-period pulsars, P ∼ 1 s, the effect of synchrotron absorption at θ - ψ « θ is found to be negligible, whereas for short-period ones, P ≤ 0.1 s, the absorption depth can be of order unity. Now the escape of radio waves from pulsar magnetospheres can be explained without any additional assumptions. At the same time, synchrotron absorption is suggested to underlie the marked distinction in the energetic characteristics of short-period and long-period pulsars proved by a number of conclusions of pulsar statistics.

Wave dispersion in gyrotropic relativistic pulsar plasmas.

Wave dispersion in a gyrotropic relativistic pulsar plasma is discussed. A pulsar plasma in general contains electrons, positrons, and possibly ions. Although electron-positron pairs are dominant in number density, charge neutrality is generally not satisfied and the gyrotropic terms need to be considered. These gyrotropic terms can lead to elliptical polarization that may be relevant for the observed circular polarization of pulsar radio emission. The wave dispersion and polarization are obtained numerically by calculating the response in terms of the three relativistic plasma dispersion functions. For waves propagating at an oblique angle (to the ambient magnetic field) a significant ellipticity requires the plasma to deviate substantially from the neutrality condition.

Surface modification of PET films by pulsed argon plasma

AbstractThe rf power was modulated (discharge on‐time of 10 μs and discharge off‐time of 50–500 μs), for pulsed argon (Ar) and oxygen (O2) plasmas used to irradiate PET film surfaces to modify the film surfaces. From data regarding the contact angle for the modified PET film surfaces and chemical analyses with XPS, effects of the rf power modulation on the surface modification are discussed. The pulsed Ar and O2 plasmas are effective in modification of the PET film surface. There is no difference in the contact angle between the pulsed plasma and the continuous plasma. Furthermore, the pulsed Ar plasma is advantageous in formation of hydroxyl groups on the PET film surfaces. The rf power modulation has a possibility to modify into peculiar surfaces. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2845–2852, 2002

Towards explanation of pulsar radio spectra

Refraction of radio waves in the ultrarelativistic highly magnetized pulsar plasma is considered. The influence of the eect on the observed pulsar spectra is studied. It is shown that refraction can cause a marked redistribution of the intensity in the emission beam. For a given sight-line trajectory across the beam this aects not only the apparent prole morphology but also the total intensity detected. As refraction is frequency-dependent, it can modify the pulsar spectrum. The spectral changes are peculiar to both the core and conal components. For the typical parameters of the magnetospheric plasma the eect is found to be ecient at the frequencies above 1 GHz. It is demonstrated that refraction can lead to the high-frequency steepening of the core-component spectrum with the subsequent flattening at still higher frequencies. In addition, the eect can account for the inversion of the intensity ratio of the conal components and the consequent break in the spectra of the conal-double pulsars. The high-frequency features of the pulsar spectra are compared with the other observational consequences of refraction. The conclusion is made that at the frequencies above 1 GHz the properties of pulsar radiation are mainly determined by the propagation eects in the magnetospheric plasma.

Quasilinear diffusion as a result of modulational instability in the pulsar plasma.

Quasilinear diffusion due to modulational instability is considered in this paper. Interaction between the high-frequency, nearly transverse O mode (or the transverse X mode) and the low-frequency, nearly longitudinal L-O mode in a pulsar magnetospheric pair plasma can lead to modulational instability. The low-frequency L-O mode is superluminal, which is not subjected to usual Landau damping, and it is possible that excess wave energy is stored in this superluminal mode. The superluminal low-frequency L-O mode can dissipate in a way similar to the process of Langmuir wave collapse, that is, it cascades from the long- to short-wavelength regimes. When the phase speed becomes less than c, the waves can be damped through various resonances. We consider, in particular, damping through cyclotron resonance, which can lead to particle acceleration. The energetic beam particles, which have a very small spread initially, can develop a high-energy distribution tail, acquiring pitch angles through quasilinear diffusion. These particles can emit gamma rays through synchrotron radiation, contributing to the observed pulsar high-energy emission.

Cyclotron absorption of radio emission within pulsar magnetospheres

Absorption of radio emission through normal cyclotron resonance within pulsar magnetospheres is considered. The optical depth for cyclotron damping is calculated using a plasma distribution with an intrinsically relativistic spread. We argue that such a broad distribution is plausible for pulsar plasmas and that it implies that a class of pulsars that should have cyclotron damping extends to include young pulsars with shorter periods and stronger magnetic fields. There is no obvious observational evidence for disruption of radio pulses, which implies that the optical depth cannot be too large. We propose that cyclotron resonance may cause marginal absorption of radio emission. It is shown that such marginal absorption produces potentially observable asymmetric features for double-peak pulse profiles with wide separation, with one peak tending to be suppressed.

Pulsar magnetospheres: Numerical simulations of large amplitude electron-positron oscillations

The numerical simulation of non-linear electron-positron oscillations is reported, showing the evolution of the electric eld and the plasma number density for large amplitude disturbances. Sharp density gradients and changes in the oscillation frequency are demonstrated, and a new analytical framework is presented to illustrate these phenomena, particularly in the context of pulsar plasmas.

Cyclotron effects on wave dispersion in pulsar plasmas

Dispersion in an intrinsically relativistic, one-dimensional, electron–positron pair plasma (a pulsar plasma) is treated exactly, generalizing earlier results that applied in the low-frequency limit and that neglected the cyclotron resonance. The general theory involves two additional relativistic plasma dispersion functions, evaluated at the normal and anomalous Doppler resonances. These two functions are associated with the non-gyrotropic and gyrotropic parts of the response respectively. The functions are evaluated for bell-type and Jüttner distributions. Wave dispersion is discussed for a non-gyrotropic pulsar plasma with a highly relativistic Alfvén speed. Emphasis is placed on crossings of the light line, defined in terms of the parallel phase velocity. Subluminal waves exist only for sufficiently small angles of propagation, and are confined to frequencies below about the mean gyrofrequency of the relativistic particles.

Wave Dispersion in Highly Relativistic Plasma

Dispersion in a highly relativistic plasma is described by a relativistic plasma dispersion function that becomes increasingly sharply peaked as the plasma becomes increasingly relativistic. Wave dispersion in a highly relativistic plasma is discussed in three contexts: low-frequency waves in a pulsar plasma (a one-dimensional, extremely strongly magnetized, pair plasma), Langmuir waves in an isotropic thermal plasma, and high-frequency waves in a synchrotron emitting gas.

The Pulsar Pair Plasma

AbstractThe anisotropic and relativistic features of the pulsar pair plasma are adequately modelled using relativistic one-dimensional Jűttner-Synge distribution functions. The dispersion relation for wave propagation in such a plasma involves coefficients that specifically depend on the distribution function of its particles. An analytical determination of these coefficients allows us to obtain characteristics of quasi-longitudinal waves together with the conditions for the unstable interaction of ultrarelativistic beam and plasma. Similar derivations concern electromagnetic waves.

Testing the two-stream instability in a pulsar magnetosphere

AbstractConditions for the development of a two-stream instability in a pulsar magnetosphere are deduced from specific dispersion relations for plane wave perturbations, that depend on the distribution functions of the involved particles. Three different approaches are investigated.Firstly, using relativistic one-dimensional Juttner Synge distribution functions appropriate to describe pulsar pair plasmas flows, we analytically derive the dispersion relation anew, precisely determining the dependence of its coefficients on the temperature, fluid velocity and associated Lorentz factor. We obtain modified frequencies for quasi-longitudinal waves and specific conditions for a two-stream instability to develop.Secondly, the importance of two-stream instabilities is tested numerically on two different timescales, that concern stationary and non-stationary properties of pair plasma flows. The linear analysis involves Gaussian distribution functions of the momentum, factorized with functions that depend on the localisation of the different groups of particles, and shows results that agree with observed luminosities.Finally as derived from fluid equations, the nonlinear evolution of such an instability process allows to associate the high level of radio radiation observed from pulsars with the existence of a lattice of radiating ‘Langmuir‘ soliton-like structures in a pulsar emission region. Actually, pair plasma particles follow the bundle of diverging magnetic field lines in the open magnetosphere and ‘Langmuir‘ soliton-like solutions, modified by magnetic field and density gradients, imply additional radiation.

First Astronomical Application of a Cryogenic Transition Edge Sensor Spectrophotometer

We report on the first astronomical observations with a photon-counting pixel detector that provides arrival time (δt = 100 ns) and energy (δEγ ≤ 0.15 eV) resolved measurements from the near-IR through the near UV. Our test observations were performed by coupling this transition edge sensor device to a 0.6 m telescope; we have obtained the first simultaneous optical near-IR phase-resolved spectra of the Crab pulsar. A varying infrared turnover gives evidence of self-absorption in the pulsar plasma. The potential of such detectors in imaging arrays from a space platform is briefly described.

Relativistic Plasma Emission and Pulsar Radio Emission: A Critique

Relativistic plasma emission due to a beam instability in the polar cap regions is examined critically as a pulsar radio emission mechanism. Wave dispersion in the pulsar plasma is discussed, based on the use of a relativistic plasma dispersion function. The growth rate for the beam instability is estimated in the rest frame of the plasma for parallel Langmuir waves, L-O mode waves, and oblique Alfven waves. The first two of these imply frequencies that are much higher than the observed frequencies for plausible parameters, suggesting that they are not viable as pulsar radio emission mechanisms. Growth of Alfven waves requires that the beam speed equal the phase speed of the Alfven waves, and this condition cannot be satisfied within the light cylinder, except for an extremely high energy beam. It is suggested that either the plasma parameters in the source region are quite different from what is currently considered plausible or the emission mechanism does not involve a beam instability. Alternative pulsar radio emission mechanisms should be explored further.

Plasma processes in pulsar magnetospheres and eclipsing binary pulsar systems

Plasma processes that may be responsible for pulsar radio emission and for eclipses observed for binary pulsars are discussed. High brightness temperature of pulsar radio emission implies that the radiation mechanism must be coherent. Several emission mechanisms are discussed. The high brightness temperature of radio emission also implies that nonlinear effect on wave propagation through pulsar magnetospheric plasmas is important and may result in radio pulse microstructure or cause fluctuation in dispersion measure. The discovery of eclipsing binary pulsars provides us with an opportunity to study nonlinear wave-wave interactions in electron-ion plasmas in the winds (or magnetospheres) of companion stars.

Chaos in relativistic electron plasma and nonlinear dynamics in oblique propagation of electrostatic waves

Nonlinear interaction between electrostatic waves propagating obliquely to an ambient uniform magnetic field, and electron plasma in relativistic formalism are analyzed in detail. Resonances among the harmonics (l) are delineated and a qualitative expression for the overlapping parameter (K) leading to stochasticisty is analytically derived. A novel feature of this analysis is revealed in the form of threshold wave amplitude (φk), especially at the onset of chaos. The interesting profiles concerning the variation of threshold amplitude with harmonics (l), magnetic field lines (B0), and wave vector (kz) pertaining to ensemble of electrostatic waves are displayed and discussed along with the phase-space topology mappings. These findings may provide important information concerning astrophysical scenarios, which include intergalactic plasmas, cosmic plasma particles, synchrotron radiation, and pulsar plasma analysis.

Generation of the electrostatic field in the pulsar magnetosphere plasma

The behavior of a relativistic electron–positron plasma in the pulsar magnetosphere is investigated. The equation of the motion of the magnetospheric plasma is discussed, from which it follows that, if the plasma particle radial velocity Vr&amp;gt;c/√ (where c is the speed of light), the centrifugal acceleration changes its sign and the particle braking begins. The stability of the magnetospheric plasma with respect to the radially oriented potential perturbations is discussed and the possibility of the electrostatic field generation in this plasma along the pulsar magnetic field lines is shown.

Effects of plasma rotation on alfv�n solitons in pulsar magnetospheres

Nonlinear Alfven wave in a hot rotating and strongly magnetized electron-positron plasma is considered. Using relativistic two fluid equations, the dispersion relation for Alfven wave in the rotating plasma is obtained. Large amplitude Alfven solitons are found to exist in the rotating pulsar plasma. Rotational effects on solitons are discussed.

Electrostatic drift vortices in a hot rotating strongly magnetized electron-positron pulsar plasma

Electrostatic drift wave in a hot rotating and strongly magnetized electron-positron pulsar plasma is considered. Using relativistic two fluid equations a pair of coupled nonlinear equations is derived. It is shown that the wave can propagate in the form of two-dimensional dipolar vortices at ultrarelativistic temperature (T≫mc2) of the plasma. The latter may affect the energy transport in the hot plasma, which can lead to a new turbulent state in the pulsar magnetosphere.

On the possibility of oscillations in the magnetosphere plasma of a pulsar in the region of closed field lines

In this paper, a dispersion relation for the spectrum of plasma oscillations in the region of closed field lines of a pulsar magnetosphere is obtained in a coordinate system rotating uniformly with the netron star. The dispersion relations for oscillations propagating along and at right angles to the closed field lines of the pulsar magnetosphere are analyzed in the cold-plasma approximation. In particular, it is shown that high-frequency cyclotron radio waves can be emitted in the pulsar plasma in the region of closed field lines.

Nonlinear theory of the generation of radiation in a pulsar plasma

Nonlinear mechanisms of generation of radiation of a pulsar plasma are considered with allowance for the electron-positron structure of the plasma. The rate of growth of the radiation energy is estimated under the condition that the cyclotron frequency does not exceed the plasma frequency. Such a condition can be realized near the light cylinder. The considered mechanisms lead to radio and infrared radiation of young pulsars and radio radiation of old pulsars. 14 references.