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In solar physics, there is a decades-old conundrum that is still unsolved. Why is the temperature of the corona so much larger than that of the surface of the Sun? To solve this, various approaches have been adopted so far, but they have certain limitations. In the present analysis, we invoke the standard Vlasov model and the steady-state Poynting theorem to unlock the mysterious coronal heating mechanism in terms of inertial and kinetic Alfvén waves whose electromagnetic energies turn into heat during wave–particle interaction. The coronal plasmas that support these waves are modelled by a non-thermal bi-kappa velocity distribution function. The non-thermal distribution function, which is assumed to pre-exist in the system, strongly influences the wave-heating process. Particularly, during heating by the waves in the inertial limit, the non-thermal features of the distribution function give rise to a unique competition (which is entirely absent in the usual Maxwellian plasmas) between waves of different perpendicular wavenumbers (kx). For small kx , when either the non-thermal parameter κ or the electron parallel temperature T ||e increases, the inertial Alfvén waves can efficiently heat the plasma in their immediate vicinity. However, for relatively large kx , an increase in either κ or T ||e enables the inertial Alfvén waves to effectively heat the plasma in remote regions in the corona. Although such competition is not seen in the kinetic limit, the non-thermal features still seem to control the heating process. The possible explanations behind the above-mentioned cases are provided by the bi-kappa velocity distribution function, which holds vital clues as to how the non-thermal features, together with kx , dictate the resonance conditions that play a crucial role in the heating process. [ABSTRACT FROM AUTHOR]

In the paradigm of magnetic launching of astrophysical jets, instabilities in the magnetohydro-dynamic (MHD) flow are a good candidate to convert the Poynting flux into the kinetic energy of the plasma. If the magnetized plasma fills the almost entire space, the jet is unstable to helical perturbations of its body. However, the growth rate of these modes is suppressed when the poloidal component of the magnetic field has a vanishing gradient, which may be the actual case for a realistic configuration. Here we show that, if the magnetized plasma is confined into a limited region by the pressure of some external medium, the velocity shear at the contact surface excites unstable modes which can affect a significant fraction of the jet's body. We find that when the Lorentz factor of the jet is Γ ∼ 10 (Γ ∼ 100), these perturbations typically develop after propagating along the jet for tens (hundreds) of jet's radii. Surface modes may therefore play an important role in converting the energy of the jet from the Poynting flux to the kinetic energy of the plasma, particularly in active galactic nuclei. The scaling of the dispersion relation with (i) the angular velocity of the field lines and (ii) the sound speed in the confining gas is discussed. [ABSTRACT FROM AUTHOR]

In this paper, we report our detailed analysis of the new strong-coupling regime between Alfvén and fast modes in Poynting-dominated plasma turbulence, reported in our previous work TL16, which is an important effect for many relativistic plasma phenomena, and calls for newtheories of Poynting-dominated magnetohydrodynamic (MHD) turbulence.We performed numerical simulations of relativistic MHD turbulence in isothermal plasmas, and analysed the ratio of fast to Alfvén mode energy. We found that the increase of the fast mode with the background σ-parameter can be observed even in isothermal plasma, showing that such a phenomena is universal in trans-Alfvénic turbulence in Poynting-dominated plasmas. To study the detailed energy conversion process, we also performed a series of simulations of decaying turbulence injecting pure Alfvén, fast, and slow modes, respectively, and investigated the development of the mode conversion from the each mode. We also found that the mode conversion between Alfvén and fast modes is nearly insensitive to the background temperature. Finally, we report a result of a simulation with initially fast mode dominated turbulence. It developed into a temporally strong-coupling regime, which is a strong evidence for the existence of our suggesting strong-coupling regime of fast and Alfvén modes. Our result suggests that the strong turbulence in Poynting-dominated plasma is very different from that in the non-relativistic plasma. It will also give an important guidance to studies of particle acceleration and non-thermal photon emission from Poynting-dominated plasma. [ABSTRACT FROM AUTHOR]

The bulk density of a meteoroid affects its dynamics in space, its ablation in the atmosphere, and the damage it does to spacecraft and lunar or planetary surfaces. Meteoroid bulk densities are also notoriously difficult to measure, and we are typically forced to assume a density or attempt to measure it via a proxy. In this paper, we construct a density distribution for sporadic meteoroids based on existing density measurements. We considered two possible proxies for density: the KB parameter introduced by Ceplecha and Tisserand parameter, TJ. Although KB is frequently cited as a proxy for meteoroid material properties, we find that it is poorly correlated with ablation-model-derived densities.We therefore followthe example of Kikwaya et al. in associating density with the Tisserand parameter. We fit two density distributions to meteoroids originating from Halley-type comets (TJ < 2) and those originating from all other parent bodies (TJ > 2); the resulting two-population density distribution is the most detailed sporadic meteoroid density distribution justified by the available data. Finally, we discuss the implications for meteoroid environment models and spacecraft risk assessments. We find that correcting for density increases the fraction of meteoroid-induced spacecraft damage produced by the helion/\antihelion source. [ABSTRACT FROM AUTHOR]

The collimation of a Poynting-flux dominated jet by a wind emanating from the surface of an accretion flow is computed using a semi-analytic model. The injection of the disc wind is treated as a boundary condition in the equatorial plane, and its evolution is followed by invoking a prescribed geometry of streamlines. Solutions are obtained for a wide range of disc wind parameters. It is found that jet collimation generally occurs when the total wind power exceeds about 10 percents of the jet power. For moderate wind powers, we find gradual collimation. For strong winds, we find rapid collimation followed by focusing of the jet, after which it remains narrow over many Alfvén crossing times before becoming conical. We estimate that in the later case, the jet's magnetic field may be dissipated by the current-driven kink instability over a distance of a few hundreds gravitational radii. We apply the model to M87 and show that the observed parabolic shape of the radio jet within the Bondi radius can be reproduced provided that the wind injection zone extends to several hundreds gravitational radii, and that its total power is about one-third of the jet power. The radio spectrum can be produced by synchrotron radiation of relativistically hot, thermal electrons in the sheath flow surrounding the inner jet. [ABSTRACT FROM AUTHOR]

Dust grains migrating under Poynting–Robertson drag may be trapped in mean-motion resonances with planets. Such resonantly trapped grains are observed in the Solar system. In extrasolar systems, the exozodiacal light produced by dust grains is expected to be a major obstacle to future missions attempting to directly image terrestrial planets. The patterns made by resonantly trapped dust, however, can be used to infer the presence of planets, and the properties of those planets, if the capture and evolution of the grains can be modelled. This has been done with N-body methods, but such methods are computationally expensive, limiting their usefulness when considering large, slowly evolving grains, and for extrasolar systems with unknown planets and parent bodies, where the possible parameter space for investigation is large. In this work, we present a semi-analytic method for calculating the capture and evolution of dust grains in resonance, which can be orders of magnitude faster than N-body methods. We calibrate the model against N-body simulations, finding excellent agreement for Earth to Neptune mass planets, for a variety of grain sizes, initial eccentricities, and initial semimajor axes. We then apply the model to observations of dust resonantly trapped by the Earth. We find that resonantly trapped, asteroidally produced grains naturally produce the ‘trailing blob’ structure in the zodiacal cloud, while to match the intensity of the blob, most of the cloud must be composed of cometary grains, which owing to their high eccentricity are not captured, but produce a smooth disc. [ABSTRACT FROM PUBLISHER]

Motivated by the picture of a thin accretion disc around a black hole, radiating mainly in the direction perpendicular to its plane, we study the motion of test particles interacting with a test geodesic radiation flux originating in the equatorial plane of a Schwarzschild spacetime and propagating initially in the perpendicular direction. We assume that the interaction with the test particles is modelled by an effective term corresponding to the Thomson-type interaction which governs the Poynting-Robertson effect. After approximating the individual photon trajectories adequately, we solve the continuity equation approximately in order to find a consistent flux density with a certain plausible prescribed equatorial profile. The combined effects of gravity and radiation are illustrated in several typical figures which confirm that the particles are generically strongly influenced by the flux. In particular, they are both collimated and accelerated in the direction perpendicular to the disc, but this acceleration is not enough to explain highly relativistic outflows emanating from some black hole-disc sources. The model can however be improved in a number of ways before posing further questions which are summarized in concluding remarks. [ABSTRACT FROM AUTHOR]

We consider the conditions within a Poynting-flux-dominated gamma-ray burst (GRB) emission region. Because of the enormous magnetic energy density, relativistic electrons will cool in such a region extremely rapidly via synchrotron. As there is no known mechanism that can compete in these magnetic environments with synchrotron it must be the source of the prompt sub-MeV emission. This sets strong limits on the size and Lorentz factor of the outflow. Furthermore, synchrotron cooling is too efficient. It overproduces optical and X-ray as compared with the observations. This overproduction of low-energy emission can be avoided if the electrons are re-accelerated many times (≳ 5 × 104) during each pulse (or are continuously heated) or if they escape the emitting region before cooling down. We explore the limitations of both models practically ruling out the later and demonstrating that the former requires two different acceleration mechanisms as well as an extremely large magnetic energy to Baryonic energy ratio. To be viable, any GRB model based on an emission region that is Poynting flux dominated must demonstrate how these conditions are met. We conclude that if GRB jets are launched magnetically dominated they must dissipate somehow most of their magnetic energy before they reach the emission region. [ABSTRACT FROM AUTHOR]

Properties of the solar wind are discussed and applied to the effect of the wind on motion of bodies in the Solar system. The velocity density function for the solar wind constituents is given by the κ-distribution. The relevant contributions to the solar wind action contain also the sputtering and reflection components in addition to direct impact. The solar wind effect is more important than the action of the solar electromagnetic radiation, as for the secular orbital evolution. The acceleration of a body under the action of the solar radiation, electromagnetic and corpuscular, is proportional to $[1 - (1 + \eta _{1} / \overline{Q} \ ^{\prime }_{{\rm pr}})\boldsymbol {v} \cdot \hat{\boldsymbol r}/c] \hat{\boldsymbol r}$$- (1 + \eta _{2} / \overline{Q} \ ^{\prime }_{{\rm pr}}) \boldsymbol v /c$, approximately. Here, $\overline{Q} \ ^{\prime }_{{\rm pr}}$ is the dimensionless efficiency factor of the radiation pressure, v is the body's velocity at the position vector r with respect to the Sun, c is the speed of light and η1 ≐ 1.1, η2 ≐ 1.4. The dimensionless cross-section the dust grain presents to wind pressure is about 4.7, while the conventional value is 1.0. [ABSTRACT FROM PUBLISHER]

Radio emission, polarization and Faraday rotation maps of the radio jet of the galaxy 3C 303 have shown that one knot of this jet carries a galactic-scale electric current and that it is magnetically dominated. We develop the theory of magnetically dominated or Poynting-flux jets by making an analogy of a Poynting jet with a transmission line or waveguide carrying a net current and having a potential drop across it (from the jet's axis to its radius) and a definite impedance which we derive. The electromagnetic energy flow in the jet is the jet impedance times the square of the jet current. The observed current in 3C 303 can be used to calculate the electromagnetic energy flow in this magnetically dominated jet. Time dependent but not necessarily small perturbations of a Poynting-flux jet are described by the 'telegrapher's equations'. These predict the propagation speed of disturbances and the effective wave impedance for forward and backward propagating wave components. A localized disturbance of a Poynting jet gives rise to localized dissipation in the jet which may explain the enhanced synchrotron radiation in the knots of the 3C 303 jet, and also in the apparently stationary knot HST-1 in the jet near the nucleus of the nearby galaxy M87. For a relativistic Poynting jet on parsec scales, the reflected voltage wave from an inductive termination or load can lead to a backward propagating wave which breaks down the magnetic insulation of the jet giving |E|/|B| ≥ 1. At the threshold for breakdown, |E|/|B| = 1, positive and negative particles are directly accelerated in the E x B direction which is approximately along the jet axis. Acceleration can occur up to Lorentz factors ~107. This particle acceleration mechanism is distinct from that in shock waves and that in magnetic field reconnection. [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper, we provide exact solutions for the extraction of energy from a rotating black hole via both the electromagnetic Poynting flux and matter currents. By appropriate choice of a radially independent poloidal function Λ(θ), we find solutions where the dominant outward energy flux is along the polar axis, consistent not only with a jet-like collimated outflow, but also with a weaker flux of energy along the equatorial plane. Unlike previously obtained solutions, the magnetosphere is free of magnetic monopoles everywhere. [ABSTRACT FROM AUTHOR]

ABSTRACT We construct a numerical model of emission from minijets, localized flows driven by magnetic reconnection inside Poynting-flux-dominated jets proposed to explain the ultrafast variability of blazars. The geometrical structure of the model consists of two wedge-like regions of relativistically flowing gas, separated by a stationary shock. The dynamics is based on solutions of relativistic magnetic reconnection with a guide field from Lyubarsky. Electron distributions in each region are chosen to match the pressure and density of the local plasma. Synchrotron emission from both regions is used to calculate Compton scattering, Compton drag and photon-photon opacity effects, with exact treatment of anisotropy and the Klein-Nishina regime. Radiative effects on plasma are taken into account, including the dependence of pressure on electron radiative losses and adiabatic heating of the flow decelerating under Compton drag. The results are applied to the 2006 July flare in the BL Lac object PKS 2155−304, with the aim of matching TeV flux measurements by the High Energy Stereoscopic System (HESS) with models that satisfy the variability constraints, while keeping X-ray emission below simultaneous Chandra observations. We find that models of isolated minijets with a significant guide field overproduce X-ray emission, and that we must take into account the radiative interaction of oppositely oriented minijets in order to achieve a high enough dominance by Comptonized TeV radiation. We argue that such interactions are likely to occur in a jet where there is substantial internal reconnection, producing a large number of misaligned minijets. Finally, we show that large jet magnetizations are indeed required to satisfy all observational constraints and that the effective Lorentz factor of the minijet plasma has to be larger than 50, in agreement with earlier one-zone estimates. [ABSTRACT FROM AUTHOR]