Power-law Electron Distribution Research Articles

Magnetic Fields in Radio-Quiet Quasars

As an hypothesis the sharp far–infrared turnovers in the spectra of several radio–quiet galactic nuclei [1–3] are attributed to the modifications of synchrotron emission arising from the presence of a thermal background plasma. We calculate the synchrotron emission from a power-law distribution of relativistic electrons N(γ) = Noγ–s in a large–scale random magnetic field of strength B embedded in a thermal plasma of density ne. Two major modifications of the classical vacuum theory of synchrotron emission are established [4]:A) synchrotron sources can be optically thick only in a small frequency range around the Razin -Tsytovich frequency, whereas at smaller and higher frequencies the sources are optically thin;B) at frequencies above VR the synchrotron intensity in a plasma behaves exactly the same way as in the vacuum case, whereas at frequencies below VR the intensity is exponentially reduced,

Plasma suppression of synchrotron emission from radio-quiet infrared quasars

The authors calculate the synchrotron emission from a power-law distribution of relativistic electrons in a large-scale random magnetic field of strength B embedded in the thermal plasma of density n/sub e/. Due to the presence of the plasma, two major modifications of the classical vacuum theory of synchrotron emission are established: (1) synchrotron sources can be optically thick only in a rather small frequency range around the Razin-Tsytovich frequency v/sub R/=20 (n/sub e/w/cm/sup -3/) (B/G)/sup -1/ Hz, whereas at smaller and higher frequencies the sources are optically thin; (2) at frequencies beyond v/sub R/ the synchrotron intensity in a plasma behaves exactly the same way as in the vacuum case, whereas at frequencies below v/sub R/ the emitted intensity is exponentially reduced. It is argued that the established low-frequency cutoff at v/sub R/ due to the plasma suppression may be responsible for the measured sharp cutoff in the far infrared of 23 northern sky radio-quiet IRAS (Infrared Astronomy Satellite) infrared quasars. The cutoffs in the spectra of these radio-quiet quasars may be due to the exponential suppression at frequencies >

The optical continua of extragalactic radio jets

view Abstract Citations (84) References (71) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Optical Continua of Extragalactic Radio Jets Keel, William C. Abstract Multicolor optical images have been used to measure the broad-band spectral shapes of radio jets known to show optical counterparts, and to search for such counterparts in additional objects. One new detection, the brightest knot in the NGC 6251 jet, is reported. In all cases, except part of the 3C 273 jet, the jet continua are well-represented by synchrotron spectra from truncated power-law electron distributions, with emitted-frame critical frequencies between 3 x 10^14^ and 2 x 10^15^ Hz. This may be due to fine structure in the jets or to the particle (re)acceleration process. Two hot spots (Pic A and 3C 303) differ from the jets, in showing unbroken power-law spectra from the radio to the B band. Image restoration has been used to examine the sub-arcsecond structure of the M87 jet and derived spectral shapes for various knots free of blending problems. The structure matches that seen in the radio to the 0.3" level, implying that the jet structure prevents particles from streaming freely over this distance (~30 pc). Significant changes in turnover frequencey occur from knot to knot, with an overall trend of higher frequency closer to the nucleus. Knot A is an exception, with a spectrum like the features near the core. An Appendix gives results of surface photometry for the program galaxies. Publication: The Astrophysical Journal Pub Date: June 1988 DOI: 10.1086/166400 Bibcode: 1988ApJ...329..532K Keywords: Active Galactic Nuclei; Astronomical Photometry; Color Photography; Extragalactic Radio Sources; Quasars; Radio Jets (Astronomy); Centimeter Waves; Radio Emission; Synchrotron Radiation; Astrophysics; GALAXIES: INDIVIDUAL MESSIER NUMBER: M87; GALAXIES: JETS; GALAXIES: PHOTOMETRY; QUASARS; RADIATION MECHANISMS; RADIO SOURCES: GALAXIES full text sources ADS | data products SIMBAD (15) NED (14)

SSC models for compact sources

A particular class of Synchrotron Self Compton models are discussed, assuming that a power law distribution of relativistic electrons is continuously injected throughout the source, that the radiative cooling time is shorter that the escape time, and that the magnetic to radiation energy density ratio U B/U r is greater than unity. Taking into account self absorption, the Compton to synchrotron luminosity ratio L C/L S greatly exceeds U r/U B if the injected power law electron distribution is steep. As in the model proposed, in a different context, by Zdziarski and Lamb (1986), the radiation produced by the multiple Compton process dominates the emission at all frequencies, and the overall spectrum slope is always flatter than unity.

Role of non-thermal electrons on the generation of X-ray and EUV lines in solar flares

The energy and angular distributions of electrons have been studied by combining small angle scatterings using analytical treatment with large angle collisions using Monte Caroo calculations as a function of column density for initially power-law electron distributions and incidence angles of 0, 30, and 60°. Using these distributions the X-ray and EUV line flux as a function of column density has been computed. The flux increases with increase in column density. At the initial column densities the contribution of non-thermal electrons for the production of line flux is negligible. However, it becomes significant at intermediate column densities at which the electron energy and angular distributions have non-Maxwellian nature. X-ray and EUV flux have also been calculated as a function of electron spectral index at a fixed column density. It falls steeply with increase in spectral index. The calculated flux is compared with the observations.

Analytic and numerical calculations of quantum synchrotron spectra from relativistic electron distributions

view Abstract Citations (24) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Analytic and Numerical Calculations of Quantum Synchrotron Spectra from Relativistic Electron Distributions Brainerd, J. J. ; Petrosian, V. Abstract Calculations are performed numerically and analytically of synchrotron spectra for thermal and power-law electron distributions using the single-particle synchrotron power spectrum derived from quantum electrodynamics. It is found that the photon energy at which quantum effects appear is proportional to temperature and independent of field strength for thermal spectra; quantum effects introduce an exponential roll-off away from the classical spectra. For power law spectra, the photon energy at which quantum effects appear is inversely proportional to the magnetic field strength; quantum effects produce a steeper power law than is found classically. The results are compared with spectra derived from the classical power spectrum with an energy cutoff ensuring conservation of energy. It is found that an energy cutoff is generally an inadequate approximation of quantum effects for low photon energies and for thermal spectra, but gives reasonable results for high-energy emission from power-law electron distributions. Publication: The Astrophysical Journal Pub Date: September 1987 DOI: 10.1086/165588 Bibcode: 1987ApJ...320..703B Keywords: Electron Distribution; Quantum Electrodynamics; Relativistic Particles; Synchrotron Radiation; Gamma Ray Bursts; Photons; Power Spectra; Relativistic Effects; Astrophysics; MAGNETIC FIELDS; RADIATION MECHANISMS full text sources ADS |

Quantum synchrotron spectra from semirelativistic electrons in teragauss magnetic fields

Synchrotron spectra are calculated from quantum electrodynamic transition rates for thermal and power-law electron distributions. It is shown that quantum effects appear in thermal spectra when the photon energy is greater than the electron temperature, and in power-law spectra when the electron energy in units of the electron rest mass times the magnetic field strength in units of the critical field strength is of order unity. These spectra are compared with spectra calculated from the ultrarelativistic approximation for synchrotron emission. It is found that the approximation for the power-law spectra is good, and the approximation for thermal spectra produces the shape of the spectrum accurately but fails to give the correct normalization. Single photon pair creation masks the quantum effects for power-law distributions, so only modifications to thermal spectra are important for gamma-ray bursts.

On the origin of the infrared and X-ray continua of active galactic nuclei

The continuum spectra of radio-quiet active galactic nuclei, which are steeper in the near-IR and flatter in the X-ray regime, can be produced in a synchrotron self-Compton model with a broken power law electron distribution that is flat at low, and steep at large, Lorentz factor values. While the steeper part generates the IR spectrum via synchrotron process, both parts together produce the flatter X-ray spectrum via Compton scattering. The intersection of the two spectra corresponds to equipartition between the magnetic field and synchrotron photon energy densities, giving approximately the same luminosities in the synchrotron and Compton components. The photon spectra are self-consistently computed here, taking the effects of cooling, e(+)e(-) pair production, and higher order Compton scattering into account.

Electron-positron pair production by ultrarelativistic electrons in a soft photon field

view Abstract Citations (27) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Electron-Positron Pair Production by Ultrarelativistic Electrons in a Soft Photon Field Mastichiadis, A. ; Marscher, A. P. ; Brecher, K. Abstract The fully differential cross section for photon-electron pair production is integrated numerically over phase space. Results are obtained for the astrophysically interesting case in which the interaction between an ultrarelativistic electron and a soft photon results in electron-positron pair production. The positron spectrum is a function of the energies of both the photon and the electron, as well as the angle of interaction. It is found that the energy at which the positron distribution peaks is inversely proportional to the photon energy and independent of the electron energy. The positron spectrum is integrated once more over initial electron energies for a power-law energy distribution of primary electrons. The same procedure is repeated for the recoil particle; it is shown that the peak of the recoil energy distribution depends linearly on the energy of the primary electron. Finally, semianalytical expressions are obtained for the energy losses of the primary electrons. Publication: The Astrophysical Journal Pub Date: January 1986 DOI: 10.1086/163792 Bibcode: 1986ApJ...300..178M Keywords: Computational Astrophysics; Electron-Positron Pairs; Pair Production; Photon-Electron Interaction; Relativistic Electron Beams; Electron Energy; Energy Dissipation; Energy Distribution; Gamma Rays; Positrons; Astrophysics; ELEMENTARY PARTICLES; GAMMA RAYS: GENERAL; RADIATION MECHANISMS full text sources ADS |

Detection of a sub-milliarcsecond radio component in the RS CVn system HR 1099

The RS CVn system HR 1099 was observed with a five station VLBI array at a frequency of 8.4 GHz during a strong radio outburst of approximately 400 mJy. The data are consistent with a circular Gaussian source of 0.8 + or - 0.12 milli-arcsec (FWHM), corresponding to a linear size of 4 + or - 0.6 x 10 to the 11th cm. This is comparable to the distance between the surfaces of the two stars, or to 75 percent of the diameter of the chromospherically active K star. Extrapolation of published photometric data shows that the starspot formation of HR 1099 was facing toward the observers at the times of observations. The high equivalent brightness temperature, approximately 10 billion K, is consistent with gyrosynchrotron emission from a power-law energy distribution of electrons in a magnetic field of strength about 30 gauss.

VLBI observations of the RS Canum Venaticorum binary systems UX ARIETIS and HR 1099 at 1.65 GHz

VLBI observations of the RS CVn binaries UX Arietis and HR 1099 have been made at 1.65 GHz using a three-element array with a minimum fringe spacing of 11.5 milli-arcsec. Both sources were found to be unresolved within measurement uncertainties. In both cases, the derived upper limit to the source size was comparable to the overall size of each binary system. The lower limits to the brightness temperature were 1.4 x 10 to the 10th K for UX Arietis and 2.9 x 10 to the 10th K for HR 1099. Simultaneous polarization measurements at the VLA showed 4-8 percent circular polarization and less than 2 percent linear polarization. It is found that the data are consistent with gyrosynchrotron emission from a power-law energy distribution of electrons in a magnetic field B less than or approximately equal to 6 gauss.

Generation of a High-Energy Electron Tail by Strong Langmuir Turbulence in a Plasma

Strong Langmuir turbulence has recently been described by a statistical treatment of collapsing cavities. This work is extended and corrected by derivation of a transfer rate valid for both the inertial and dissipative ranges, and the power-law distribution of fast electrons is obtained. Self-consistent modifications of similarity laws are calculated in the dissipative range, which change dramatically the conventional features of collapse. Limitations to collapse are also discussed.

Microwaves and hard X-rays from solar flares - Multithermal and nonthermal interpretations

It is generally accepted that the hard X rays and centimeter-wavelength (microwave) radio emission from impulsive solar flares come from a common source. The present investigation is concerned with the development of a model for impulsive hard X rays and microwaves under the assumption that they arise from the same distribution of electrons, possibly, but not necessarily, from the same volume of space. An examination is conducted of a model in which the hard X rays and microwaves are produced in a homogeneous volume by a power-law electron distribution (nonthermal model). An investigation is also performed of a multithermal model in which the hard X rays and microwaves come from an inhomogeneous source, a nest of magnetic arches in which the highest temperature electrons are confined to a small core, and where, away from the core, the temperature decreases. It is found that more or less satisfactory models can be constructed using either multithermal or nonthermal, power-law electron distributions.

Relativistic jets as X-ray and gamma-ray sources

view Abstract Citations (585) References (63) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Relativistic jets as X-ray and gamma-ray sources. Konigl, A. Abstract The radiation from beamed relativistic jets associated with bright compact extragalactic radio sources is considered and used in the interpretation of extragalactic X-ray and gamma-ray sources. Synchrotron and inverse-Compton spectra of an inhomogeneous relativistic jet are calculated on the basis of a power-law relativistic electron distribution emission model for the cases of a resolved jet and an unresolved inhomogeneous jet. It is shown that the source nonuniformity in an unresolved jet may give rise to a spectrum quite different from the local emission spectrum. The model is then applied to the spectra of BL Lac objects and the quasar 3C 273, and it is pointed out that various observed features in BL Lac object spectra and the radio and gamma-ray emission from 3C 273 may be attributed to relativistic jets. In addition, the postulated local synchrotron spectrum is applied to the resolved X-ray jet in Cen A. Publication: The Astrophysical Journal Pub Date: February 1981 DOI: 10.1086/158638 Bibcode: 1981ApJ...243..700K Keywords: Bl Lacertae Objects; Gamma Ray Astronomy; Radio Sources (Astronomy); Relativistic Particles; X Ray Sources; Emission Spectra; Optical Thickness; Quasars; Synchrotron Radiation; Astrophysics full text sources ADS | data products NED (9) SIMBAD (4)

On the physical environment in the nucleus of Centaurus A /NGC 5128/

A model is proposed for the radio and X-ray variability of the nucleus of Centaurus A in which an adiabatically expanding plasma containing a power-law distribution of relativistic electrons produces the radio flux by synchrotron emission, and the X-ray flux by inverse Compton scattering of an ambient distribution of thermal photons. The variability of Centaurus A is shown to be consistent with the expansion of an initially opaque, hot (1000-10,000 K) plasma which eventually becomes optically thin. Radio flares without corresponding X-ray flares are possible in this model because the plasma density decreases during the expansion, allowing radio radiation previously absorbed or suppressed to be observed. Some consequences of the model for the physical environment in galactic nuclei are discussed.

Particle acceleration by strong plasma turbulence. I - Acceleration of electrons to mildly relativistic energies

The problem of converting a fairly narrow nonrelativistic electron distribution into a broad power-law distribution extending to mildly relativistic energies (500 keV) is considered. When the initial electron distribution is sufficiently unstable to produce a level of electron plasma waves which exceeds the threshold for modulational instability, also known as strong electron plasma waves turbulence, the following sequence occurs. Regions of reduced plasma density and enhanced plasma wave energy density known as cavitons are formed in the plasma. Due to the self-focusing properties of electron plasma waves, these cavitons contract, which reduces the wavelength of the plasma waves trapped in the cavitons and decreases their phase velocities. These waves then interact with and accelerate a large number of electrons from the tail of the main body of the distribution to mildly relativistic energies. The problem of the initial generation of the electron plasma wave turbulence from particle distributions with a streaming electron component or an extended electron tail is considered. The state of current research on the nonlinear state of the modulational instability and its electron acceleration potential are reviewed. Finally, the question of how these results apply to astrophysical situations and how power-law electron distributions are formed is discussed.