Relativistic Radiation Research Articles

Local existence and singularities formation for isothermal relativistic radiation hydrodynamics equations

We study the Cauchy problem for multi-dimensional compressible relativistic hydrodynamics in the presence of a radiation field. First, based on the theory of quasilinear symmetric hyperbolic, we establish the local existence of smooth solutions for both non-vacuum and vacuum cases. Next, in the spirit of Sideris’ work [T. Sideris, Formation of singularities of solutions to nonlinear hyperbolic equations, Arch. Ration. Mech. Anal. 86 (1984) 369–381; T. Sideris, Formation of singularities in three-dimensional compressible fluids, Comm. Math. Phys. 101 (1985) 475–485], we show that smooth solutions blow-up in finite time if the initial data is compactly supported and large enough. Compared with the previous work, the main difficulties of the first problem lie in two aspects, we must first deal with the source terms relying on radiative quantities, and we also need to solve out the new coefficients matrices under the Lorentz transformation for vacuum case. The second difficulty arises on how to verifying that the smooth solution has finite propagation speed..

General relativistic radiative transfer code in rotating black hole space–time: ARTIST

We present a general relativistic radiative transfer code, ARTIST (Authentic Radiative Transfer In Space–Time), that is a perfectly causal scheme to pursue the propagation of radiation with absorption and scattering around a Kerr black hole. The code explicitly solves the invariant radiation intensity along null geodesics in the Kerr–Schild coordinates, and therefore properly includes light bending, Doppler boosting, frame dragging, and gravitational redshifts. The notable aspect of ARTIST is that it conserves the radiative energy with high accuracy, and is not subject to the numerical diffusion, since the transfer is solved on long characteristics along null geodesics. We first solve the wavefront propagation around a Kerr black hole that was originally explored by Hanni. This demonstrates repeated wavefront collisions, light bending, and causal propagation of radiation with the speed of light. We show that the decay rate of the total energy of wavefronts near a black hole is determined solely by the black hole spin in late phases, in agreement with analytic expectations. As a result, the ARTIST turns out to correctly solve the general relativistic radiation fields until late phases as t ∼ 90 M. We also explore the effects of absorption and scattering, and apply this code for a photon wall problem and an orbiting hotspot problem. All the simulations in this study are performed in the equatorial plane around a Kerr black hole. The ARTIST is the first step to realize the general relativistic radiation hydrodynamics.

Three-dimensional, global, radiative GRMHD simulations of a thermally unstable disc

We present results of a set of three-dimensional, general relativistic radiation magnetohydrodynamics simulations of thin accretion discs around a non-rotating black hole to test their thermal stability. We consider two cases, one that is initially radiation pressure dominated and expected to be thermally unstable and another that is initially gas-pressure dominated and expected to remain stable. Indeed, we find that cooling dominates over heating in the radiation pressure dominated model, causing the disc to collapse vertically on roughly the local cooling timescale. We also find that heating and cooling within the disc have a different dependence on the mid-plane pressure, a prerequisite of thermal instability. Comparison of our data with the relevant thin-disc thermal equilibrium curve suggests that our disc may be headed for the thermally stable, gas-pressure-dominated branch. However, because the disc collapses to the point that we are no longer able to resolve it, we had to terminate the simulation. On the other hand, the gas pressure dominated model, which was run for twice as long as the radiation pressure dominated one, remains stable, with heating and cooling roughly in balance. Finally, the radiation pressure dominated simulation shows some evidence of viscous instability. The strongest evidence is in plots of surface density, which show the disc breaking up into rings.

A solution to unconstrained Einstein’s equations for a relativistic radiation sphere

AbstractWe describe an application of a solution to unconstrained Einstein’s field equations (Ni, 2011) as a qualitative model for a relativistic radiation sphere, an object that may resemble a quasar with an extended galactic-scale ‘corona’ that resembles behaviors explained by dark matter.

Highly relativistic radiation belt electron acceleration, transport, and loss: Large solar storm events of March and June 2015.

Two of the largest geomagnetic storms of the last decade were witnessed in 2015. On 17 March 2015, a coronal mass ejection‐driven event occurred with a Dst (storm time ring current index) value reaching −223 nT. On 22 June 2015 another strong storm (Dst reaching −204 nT) was recorded. These two storms each produced almost total loss of radiation belt high‐energy (E ≳ 1 MeV) electron fluxes. Following the dropouts of radiation belt fluxes there were complex and rather remarkable recoveries of the electrons extending up to nearly 10 MeV in kinetic energy. The energized outer zone electrons showed a rich variety of pitch angle features including strong “butterfly” distributions with deep minima in flux at α = 90°. However, despite strong driving of outer zone earthward radial diffusion in these storms, the previously reported “impenetrable barrier” at L ≈ 2.8 was pushed inward, but not significantly breached, and no E ≳ 2.0 MeV electrons were seen to pass through the radiation belt slot region to reach the inner Van Allen zone. Overall, these intense storms show a wealth of novel features of acceleration, transport, and loss that are demonstrated in the present detailed analysis.

Relativistic drag and emission radiation pressures in an isotropic photonic gas

By invoking the relativistic spectral radiance, as derived by Lee and Cleaver,1 the drag radiation pressure of a relativistic planar surface moving through an isotropic radiation field, with which it is in thermal equilibrium, is determined in inertial and non-inertial frames. The forward- and backward-directed emission radiation pressures are also derived and compared. A fleeting (inertial frames) or ongoing (some non-inertial frames) Carnot cycle is shown to exist as a result of an intra-surfaces temperature gradient. The drag radiation pressure on an object with an arbitrary frontal geometry is also described.

Modelling long GRBs using a single shock with relativistic radiation hydrodynamics

We explore the possibility that a single relativistic shock, where the gas dynamics is coupled with radiation, can fit the light curves of long GRBs. For this we numerically solve the one dimensional relativistic radiation hydrodynamics equations with a single initial shock. We calculate light curves due to the evolution of this shock in terms of the velocity of the shock, the opacity of the gas, mass density and density of radiated energy. We explore how the variation of each of these parameters provides different features in the light curves. As examples we include the fitting of two long GRBs.

ПРОБЛЕМА КОВАРИАНТНОСТИ В РЕЛЯТИВИСТСКОЙ ТЕОРИИ ИЗЛУЧЕНИЯ

ПРОБЛЕМА КОВАРИАНТНОСТИ В РЕЛЯТИВИСТСКОЙ ТЕОРИИ ИЗЛУЧЕНИЯ

Radiation source for medical X-ray examination, based on the use of electron radiation during channeling in crystals

One of the possible applications of relativistic electron radiation during channeling in crystals, i.e., the use of radiation for medical visualization, is considered.A setup scheme is proposed, the results of numerical simulation of electron dynamics in crystals and radiation generation and the results of calculations of dose loads are presented.

Oscillations of radiation pressure supported tori near black holes

We study the dynamics of radiation pressure supported tori around Schwarzschild black holes, focusing on their oscillatory response to an external perturbation. Using KORAL, a general relativistic radiation hydrodynamics code capable of modeling all radiative regimes from the optically thick to the optically thin, we monitor a sample of models at different initial temperatures and opacities, evolving them in two spatial dimensions for $\sim 165$ orbital periods. The dynamics of models with high opacity is very similar to that of purely hydrodynamics models, and it is characterized by regular oscillations which are visible also in the light curves. As the opacity is decreased, the tori quickly and violently migrate towards the gas-pressure dominated regime, collapsing towards the equatorial plane. When the spectra of the $L_2$ norm of the mass density are considered, high frequency inertial-acoustic modes of oscillations are detected (with the fundamental mode at a frequency $68 M_{\rm BH}^{-1}\,\rm Hz$), in close analogy to the phenomenology of purely hydrodynamic models. An additional mode of oscillation, at a frequency $129 M_{\rm BH}^{-1}\,\rm Hz$, is also found, which can be unambiguously attributed to the radiation. The spectra extracted from the light curves are typically more noisy, indicating that in a real observation such modes would not be easily detected.

Properties of magneto-dipole X-ray lines in different radiation models

We compare polarization properties of the cyclotron, and relativistic dipole radiation of electrons moving in the magnetic field on a helix with ultra-relativistic longitudinal and non-relativistic transverse velocity components. The applicability of these models in the case of accretion onto a neutron star is discussed. The test, based on polarization observations is suggested, to distinguish between the cyclotron, and relativistic dipole origin of features, observed in X-ray spectra of some X-ray sources, among which the Her X-1 is the most famous.

On the stability of triangular points in the relativistic R3BP with oblate primaries and bigger radiating

We consider a version of the relativistic R3BP which includes the effects of oblateness of the primaries and radiation of the bigger primary as well on the stability of triangular points. We observe that the positions of the triangular points and their stability are affected by the relativistic effect apart from the radiation and oblateness of the primaries. It is further seen for these points that the range of stability region increases or decreases according as the part of the critical mass value, depending upon relativistic terms, radiation and oblateness coefficients, is positive or negative. A numerical exploration shows that in the Sun–Saturn, Sun–Uranus, Sun–Neptune systems, the oblateness has no influence on their positions and range of stability region; whereas it has a little influence on the Sun–Mars, Sun–Jupiter systems. On the other hand, we found that radiation pressure has an observable effect on the solar system.

Photon-conserving Comptonization in simulations of accretion discs around black holes

We introduce a new method for treating Comptonization in computational fluid dynamics. By construction, this method conserves the number of photons. Whereas the traditional ‘blackbody Comptonization’ approach assumes that the radiation is locally a perfect blackbody and therefore uses a single parameter, the radiation temperature, to describe the radiation, the new ‘photon-conserving Comptonization’ approach treats the photon gas as a Bose–Einstein fluid and keeps track of both the radiation temperature and the photon number density. We have implemented photon-conserving Comptonization in the general relativistic radiation magnetohydrodynamical code koral and we describe its impact on simulations of mildly supercritical black hole accretion discs. We find that blackbody Comptonization underestimates the gas and radiation temperature by up to a factor of 2 compared to photon-conserving Comptonization. This discrepancy could be serious when computing spectra. The photon-conserving simulation indicates that the spectral colour correction factor of the escaping radiation in the funnel region of the disc could be as large as 5.

SHOCK WAVE STRUCTURE IN ASTROPHYSICAL FLOWS WITH AN ACCOUNT OF PHOTON TRANSFER

For an accurate treatment of the shock wave propagation in high-energy astrophysical phenomena, such as supernova shock breakouts, gamma-ray bursts and accretion disks, knowledge of radiative transfer plays a crucial role. In this paper we consider one-dimensional (1D) special relativistic radiation hydrodynamics by solving the Boltzmann equation for radiative transfer. The structure of a radiative shock is calculated for a number of shock tube problems, including strong shock waves, and relativistic- and radiation-dominated cases. Calculations are performed using an iterative technique that consistently solves the equations of relativistic hydrodynamics and relativistic comoving radiative transfer. A comparison of radiative transfer solutions with the Eddington approximation and the M1 closure is made. A qualitative analysis of moment equations for radiation is performed and the conditions for the existence of jump discontinuity for non-relativistic cases are investigated numerically.

Efficiency of super-Eddington magnetically-arrested accretion

Abstract The radiative efficiency of super-Eddington accreting black holes (BHs) is explored for magnetically-arrested discs, where magnetic flux builds-up to saturation near the BH. Our three-dimensional general relativistic radiation magnetohydrodynamic (GRRMHD) simulation of a spinning BH (spin a/M = 0.8) accreting at ∼50 times Eddington shows a total efficiency ∼50 per cent when time-averaged and total efficiency ≳ 100 per cent in moments. Magnetic compression by the magnetic flux near the rotating BH leads to a thin disc, whose radiation escapes via advection by a magnetized wind and via transport through a low-density channel created by a Blandford–Znajek (BZ) jet. The BZ efficiency is sub-optimal due to inertial loading of field lines by optically thick radiation, leading to BZ efficiency ∼40 per cent on the horizon and BZ efficiency ∼5 per cent by r ∼ 400rg (gravitational radii) via absorption by the wind. Importantly, radiation escapes at r ∼ 400rg with efficiency η ≈ 15 per cent (luminosity L ∼ 50LEdd), similar to η ≈ 12 per cent for a Novikov–Thorne thin disc and beyond η ≲ 1 per cent seen in prior GRRMHD simulations or slim disc theory. Our simulations show how BH spin, magnetic field, and jet mass-loading affect these radiative and jet efficiencies.

Source and seed populations for relativistic electrons: Their roles in radiation belt changes

AbstractStrong enhancements of outer Van Allen belt electrons have been shown to have a clear dependence on solar wind speed and on the duration of southward interplanetary magnetic field. However, individual case study analyses also have demonstrated that many geomagnetic storms produce little in the way of outer belt enhancements and, in fact, may produce substantial losses of relativistic electrons. In this study, focused upon a key period in August–September 2014, we use GOES geostationary orbit electron flux data and Van Allen Probes particle and fields data to study the process of radiation belt electron acceleration. One particular interval, 13–22 September, initiated by a short‐lived geomagnetic storm and characterized by a long period of primarily northward interplanetary magnetic field (IMF), showed strong depletion of relativistic electrons (including an unprecedented observation of long‐lasting depletion at geostationary orbit) while an immediately preceding, and another immediately subsequent, storm showed strong radiation belt enhancement. We demonstrate with these data that two distinct electron populations resulting from magnetospheric substorm activity are crucial elements in the ultimate acceleration of highly relativistic electrons in the outer belt: the source population (tens of keV) that give rise to VLF wave growth and the seed population (hundreds of keV) that are, in turn, accelerated through VLF wave interactions to much higher energies. ULF waves may also play a role by either inhibiting or enhancing this process through radial diffusion effects. If any components of the inner magnetospheric accelerator happen to be absent, the relativistic radiation belt enhancement fails to materialize.

Bhlight: GENERAL RELATIVISTIC RADIATION MAGNETOHYDRODYNAMICS WITH MONTE CARLO TRANSPORT

We present bhlight, a numerical scheme for solving the equations of general relativistic radiation magnetohydrodynamics using a direct Monte Carlo solution of the frequency-dependent radiative transport equation. bhlight is designed to evolve black hole accretion flows at intermediate accretion rate, in the regime between the classical radiatively efficient disk and the radiatively inefficient accretion flow (RIAF), in which global radiative effects play a sub-dominant but non-negligible role in disk dynamics. We describe the governing equations, numerical method, idiosyncrasies of our implementation, and a suite of test and convergence results. We also describe example applications to radiative Bondi accretion and to a slowly accreting Kerr black hole in axisymmetry.

Kinematic Identification of the Angular Power Distribution and the Linear Polarization of Radiation of an Arbitrarily Moving Charge

Methods of the classical theory of relativistic radiation are used to investigate general properties of the total angular power distribution of radiation of a charge and to analyze the corresponding components of linearly polarized radiation emitted by this charge.

Relativistic electron precipitation induced by EMIC‐triggered emissions in a dipole magnetosphere

AbstractWe perform test particle simulations of relativistic electrons interacting with electromagnetic ion cyclotron (EMIC)‐triggered emissions in the plasmasphere. EMIC‐triggered emissions are generated by energetic protons injected into the inner magnetosphere. EMIC‐triggered emissions are characterized by large wave amplitudes, rising‐tone frequencies, and coherent left‐hand circularly polarized waves. We study trajectories of relativistic radiation belt electrons drifting eastward interacting with longitudinally distributed EMIC‐triggered emissions. Some electrons are trapped by wave potentials and efficiently guided down to lower pitch angles. Repeated interactions occur due to the mirror motion and result in the scattering of particles into the loss cone. We use two EMIC wave models for the test particle simulations. One assumes that the wave amplitude is constant, and the other assumes a time‐dependent wave amplitude that characterizes subpackets. Both model waves are resonant with 0.5–6.0 MeV electrons and precipitate them. Electrons in the energy range 1.1–3.0 MeV are precipitated most efficiently. Approximately 50% of the total injected number of 1.1–3.0 MeV electrons are precipitated in a timescale of 2 min. We obtain the relativistic electron distribution in equatorial pitch angle and in pitch angle at the atmosphere. Further, we determine the timing and longitudinal location of the relativistic electron precipitation with respect to different particle energies.

Simulation of ULF wave‐modulated radiation belt electron precipitation during the 17 March 2013 storm

AbstractBalloon‐borne instruments detecting radiation belt precipitation frequently observe oscillations in the millihertz frequency range. Balloons measuring electron precipitation near the poles in the 100 keV to 2.5 MeV energy range, including the MAXIS, MINIS, and most recently the Balloon Array for Relativistic Radiation belt Electron Losses balloon experiments, have observed this modulation at ULF wave frequencies. Although ULF waves in the magnetosphere are seldom directly linked to increases in electron precipitation since their oscillation periods are much larger than the gyroperiod and the bounce period of radiation belt electrons, test particle simulations show that this interaction is possible. Three‐dimensional simulations of radiation belt electrons were performed to investigate the effect of ULF waves on precipitation. The simulations track the behavior of energetic electrons near the loss cone, using guiding center techniques, coupled with an MHD simulation of the magnetosphere, using the Lyon‐Fedder‐Mobarry code, during a coronal mass ejection (CME)‐shock event on 17 March 2013. Results indicate that ULF modulation of precipitation occurs even without the presence of electromagnetic ion cyclotron waves, which are not resolved in the MHD simulation. The arrival of a strong CME‐shock, such as the one simulated, disrupts the electric and magnetic fields in the magnetosphere and causes significant changes in both components of momentum, pitch angle, and L shell of radiation belt electrons, which may cause them to precipitate into the loss cone.