Inverse compton scattering in anisotropic synchrotron sources

Models of compact, high brightness temperature sources such as quasars and active galactic nuclei often predict substantial inverse-compton scattered flux to be produced at high frequencies. As these fluxes are not observed, it is necessary to assume that extreme relativistic and/or anisotropic effects dominate the source. The often used equations to include these effects however are derived with several simplifying assumptions, which may not always be consistent with the derived source parameters (for example, the assumption of no time dependence in a violently variable quasar may not be appropriate). We therefore present here an explicit derivation of the dependence of the rate of inverse compton scattering on anisotropies in the source, to emphasise the importance and number of assumptions required in the derivation.     

Compton scattering of relativistic electrons in compact X-ray sources

The problem of single Compton scattering is considered and the resulting spectrum, angular distribution and polarization of scattered photons in a general case are obtained. The inverse Compton scattering (ICS) for arbitrary energies of electronsE and photons ₀ is investigated in detail. In the case of isotropically-distributed initial photons and relativistic electrons, a strong rise of the scattered spectrum near the upper edge takes place, starting from the values of the characteristic parameterb4E ₀10 (in units of mc²=1). The energy-loss rate of relativistic electrons due to ICS is calculated. It is shown that the relativistic electrons of the energiesE100 MeV, when scattering on the X-rays with ₀~10KeV, transmit the dominant part of their energy to the photons which fall after scattering into the energy range of the electrons (100 MeV).The radiation spectrum of ICS, as well as the energy-losses of relativistic electrons distributed by power-lawE ^–, are calculated. The radiation spectrum reveals the power-law behaviour with the different indices in two limits: the dependence ^–(1)/2 at ₀1 gradually changes to ^–(+1) ln (₀) law for ₀1.     

Resonant Compton scattering associated with pair creation

Studies of Compton scattering by relativistic electrons in a strong magnetic field have been restricted to either incident photon angles θ′ aligned along the magnetic field B or incident photon energies ω′ below the first pair creation threshold $\omega'_{PC}$ . When these restrictions are relaxed there is a resonance in Compton scattering associated with pair creation (PC), that is analogous to but independent of known resonances associated with gyromagnetic absorption (GA). As with the GA resonances, that may be labeled by the Landau quantum numbers of the relevant states, there is a sequence of PC resonances where the scattering cross section diverges. In this paper, the lowest divergence is studied for incident photon energies satisfying ω′²sin² θ′/(2eB)?1, assuming that the scattering electron is in its ground (Landau) state. This lowest resonance affects only parallel-polarized photons.     

Radiative transfer with Compton scattering in plane parallel geometry

We have solved the equation of radiative transfer with Compton scattering. The specific intensity has been expanded by Taylor series with respect to wavelength and the first three terms have been retained in solving the transfer equation. It is noted that in a medium stratified in plane parallel layers, the multiple Compton scattering redistributes the initial energy over a range of 3 to 5 Compton wavelengths. A good fraction of the incident radiation is transferred across the layer with redistribution in wavelength, the actual value depending on the optical thickness of the medium     

Compton scattering in strong magnetic field

Using rigorous quantum electromagnetic method, I have calculated the Compton scattering cross-section in a strong magnetic field. The formula obtained (Eq. (6)) is not only general, but also simple. It reduces to Herold's result [3] in the electron rest frame, when the electron is at the lowest Landau level. Numerical calculation of the cross-section was carried out in several selected cases and the results are given in TABLES 1–4.     

On Field's Compton scattering instability

A more detailed treatment of instabilities arising from the interaction between an electron gas and a radiation field than that given by Field (1971) is described.     

Inverse Compton scattering – revisited

The inverse Compton scattering of high energy electrons by photons is discussed and a simple derivation of the total power radiated is presented. The derivation is completely classical and exhibits clearly why similar formulas are applicable in the case of inverse compton scattering and synchroton radiation.     

Multiple Compton scattering in strongly magnetized plasma

To provide the necessary data for solving the mystery of the γ-ray burst spectrum, we solved the equation of transport of γ photons in a strongly magnetized, purely scattering plasma. We mainly discussed the effect of multiple scattering on the annihilation line photons and γ-ray continuum. In our calculations we assumed the scattering layer to be a non-degenerate plasma with a temperature between (+7)K and (+8)K, and a strong magnetic field of 4.414(+12)G. We used the precise Compton cross-section for a strong field. The effect of the strong field as shown by the results of our calculation will help to gain a deeper understanding of the γ-ray burst spectrum.     

Induced Compton scattering by relativistic particles

Equations describing the evolution of isotropic distributions of unpolarized electromagnetic waves and of scattering of any energy due to spontaneous and induced Compton scattering are derived in the semi-classical approximation for unshielded particles.It is shown that induced Compton scattering of high frequency waves by relativistic electrons in synchrotron sources is a negligible effect contrary to the conclusions of Oster (1968b) and of Kaplan and Tsytovich (1969).     

Radio spectra of synchrotron sources with spherical symmetry

This paper deals with the radio spectra of synchrotron sources with spherically symmetric non-homogeneities. It is pointed out that the Type-c spectra can be produced by such a non-homogeneity even if the source is optically thin. This model is particularly advantageous in interpreting sources with no compact characteristics and yet showing a Type-c spectrum, and the observed decrease in source size with increasing frequency. In addition, it is possible to give a uniform interpretation of the four spectral types on the basis of such a non-homogeneity.     

Compton scattering of electromagnetic radiation in pulsar magnetospheres

We have considered the spontaneous Compton scattering of radiation in the magnetic field by both a single ultra-relativistic electron and a system of electrons with the power-law energy distribution. The degree of radiation anisotropy was assumed arbitrary. Parameters of the scattering-generated radiation for the entire range of post-scattering photon energies are given in the paper for all possible scattering modes.     

Compton attenuation coefficient in scattering by maxwellian electrons

Equations for the coefficient of attenuation of radiation due to Compton scattering by a thermal electron gas with an arbitrary temperature are summarized. A new representation is also obtained for the integral through which the attenuation coefficient, averaged over a relativistic, Maxwellian energy distribution of electrons, is expressed. This representation enables one to efficiently calculate the coefficient for a hightemperature electron gas. The accuracy of an approximate expression for the attenuation coefficient, corresponding to the assumption that scattering is isotropic in the rest frame of an electron, is also estimated. Translated from Astrofizika, Vol. 43, No. 3, pp. 473-482, July–September, 2000.     

On induced Compton scattering by relativistic particles

Induced Compton scattering by independent relativistic particles in a radiation field is considered from both quantum mechanical and classical viewpoints. Quantum mechanically, the particle recoil causes an imperfect cancellation of the induced scattering rates between pairs of photon states. This results in a net energy transfer from the radiation field to the particle. Classically, the electrodynamical effects are manifestations of non-linear coupling between different wave amplitudes in the equation of motion. The results from these two approaches are related and shown to be equivalent.     

Probing pulsar winds using inverse Compton scattering

We investigate the effects of inverse Compton scattering by electrons and positrons in the unshocked winds of rotationally-powered binary pulsars. This process can scatter low energy target photons to produce gamma rays with energies from MeV to TeV. The binary radio pulsars PSR B1259−63 and PSR J0045−73 are both in close eccentric orbits around bright main sequence stars which provide a huge density of low energy target photons. The inverse Compton scattering process transfers momentum from the pulsar wind to the scattered photons, and therefore provides a drag which tends to decelerate the pulsar wind. We present detailed calculations of the dynamics of a pulsar wind which is undergoing inverse Compton scattering, showing that the deceleration of the wind of PSR B1259−63 due to ‘inverse Compton drag' is small, but that this process may confine the wind of PSR J0045−73 before it attains pressure balance with the outflow of its companion star. We calculate the spectra and light curves of the resulting inverse Compton emission from PSR B1259−63 and show that if the size of the pulsar wind nebula is comparable to the binary separation, then the γ-ray emission from the unshocked wind may be detectable by atmospheric Cherenkov detectors or by the new generation of satellite-borne γ-ray detectors such as INTEGRAL and GLAST. This mechanism may therefore provide a direct probe of the freely-expanding regions of pulsar winds, previously thought to be invisible.     

On the isotropization of electrons in synchrotron sources

Electrons radiating synchrotron radiation develop a pitch angle anisotropy, and so become unstable to the coherent emission of hydromagnetic waves. The evolution of the coupled system of anisotropic electrons and waves is studied in the absence of any dissipation of the waves in the ambient medium. The anisotropy of the electrons approaches a steady state in which the anisotropy is energy independent and of orderv _A/c (v _A=Alfvén speed). The conditions for this small degree of anisotropy to be maintained are examined.Due to this scattering the bend in the synchrotron spectrum, from an inverse power law with index to one with index 4/3+1, due to an initial or recurrent injection of electrons, could only occur at infrared or higher frequencies.     

Magnetic field strength estimation in synchrotron radiation sources

In this paper a method of estimating the magnetic field strength,B, in a homogeneous microwave burst source with simplified expressions for the synchrotron radiation is presented. An approximate formula of the magnetic field is obtained using the method. Once the magnetic field is estimated the total number of energetic electrons along the line of sightN L can be estimated also. The errors ofB andN L have been given. It is found that this method is useful for semiquantitative investigations of models of radio burst sources.     

Effects of non-thermal tails in Maxwellian electron distributions on synchrotron and Compton processes

We investigate how the presence of a non-thermal tail beyond a Maxwellian electron distribution affects the synchrotron process as well as Comptonization in plasmas with parameters typical for accretion flows on to black holes. We find that the presence of the tail can significantly increase the net (after accounting for self-absorption) cyclo-synchrotron emission of the plasma, which then provides seed photons for Compton upscattering. Thus, the luminosity in the thermally Comptonized spectrum is enhanced as well. The importance of these effects increases with both increasing Eddington ratio and black hole mass. The enhancement of the Comptonized synchrotron luminosity can be as large as ∼10³ and ∼10⁵ for stellar and supermassive black holes, respectively, when the energy content in the non-thermal tail is 1 per cent.
The presence of the tail only weakly hardens the thermal Comptonization spectrum but it leads to the formation of a high-energy tail beyond the thermal cut-off, which two effects are independent of the nature of the seed photons. Since observations of high-energy tails in Comptonization spectra can constrain the non-thermal tails in the electron distribution and thus the Comptonized synchrotron luminosity, they provide upper limits on the strength of magnetic fields in accretion flows. In particular, the measurement of an MeV tail in the hard state of Cyg X-1 by McConnell et al. implies the magnetic field strength in this source to be at most an order of magnitude below equipartition.     

Inverse Compton scattering model for gamma-ray production in MeV blazars

It is proposed that the spectra of so-called 'MeV blazars' can be explained in terms of previously developed models of the external Comptonization of accretion disc radiation, provided that the structure of the inner and outer parts of the accretion disc is different. The electron acceleration is saturated by the inverse Compton losses in the inner geometrically thick disc and the outer geometrically thin disc at different maximum energies; this causes the appearance of two spectral components, one strongly peaked in the MeV energy range and the other of a power-law type extending through the GeV energy range. The spectra, computed in terms of such a simple geometrical model, are in good agreement with observations of the MeV blazar PKS 0208−512. They are consistent with the transient appearance of a strong MeV peak, the power-law spectrum in the EGRET energy range, and a possible cut-off at high energies.     

X-ray polarization signatures of Compton scattering in magnetic cataclysmic variables

Compton scattering within the accretion column of magnetic cataclysmic variables (mCVs) can induce a net polarization in the X-ray emission. We investigate this process using Monte Carlo simulations and find that significant polarization can arise as a result of the stratified flow structure in the shock-ionized column. We find that the degree of linear polarization can reach levels up to ∼8 per cent for systems with high accretion rates and low white dwarf masses, when viewed at large inclination angles with respect to the accretion column axis. These levels are substantially higher than previously predicted estimates using an accretion column model with uniform density and temperature. We also find that for systems with a relatively low-mass white dwarf accreting at a high accretion rate, the polarization properties may be insensitive to the magnetic field, since most of the scattering occurs at the base of the accretion column where the density structure is determined mainly by bremsstrahlung cooling instead of cyclotron cooling.