Compact Synchrotron Sources Research Articles

Laser synchrotron radiation as a compact source of tunable, short pulse hard X-rays

A compact laser synchrotron source (LSS) is proposed as a means of generating tunable, narrow bandwidth, ultrashort pulses of hard X-rays. The LSS is based on the Thomson backscattering of intense laser radiation from a counterstreaming electron beam. Advances in both compact ultraintense solid-state lasers and high brightness rf linac beams make the LSS an attractive compact source of high brightness X-rays, particularly at photon energies beyond ∼ 30 keV. The spectral flux, brightness, bandwidth and pulse structure are analyzed. In the absence of filtering the spectral bandwidth in the LSS is typically ⪅ 1% and is limited by electron beam emittance and energy spread. Two configurations of the LSS are discussed, one providing high peak power and the other high average power.

Tunable, short pulse hard x-rays from a compact laser synchrotron source

A compact laser synchrotron source (LSS) is proposed as a means of generating tunable, narrow bandwidth, ultra-short pulses of hard x rays. The LSS is based on the Thomson backscattering of intense laser radiation from a counterstreaming electron beam. Advances in both compact ultra-intense solid-state lasers and high brightness electron accelerators make the LSS an attractive compact source of high brightness pulsed x rays, particularly at photon energies beyond ∼30 keV. The x-ray wavelength is λ[Å]=650 λ0[μm]/Eb2[MeV], where λ0 is the laser wavelength and Eb is the electron beam energy. For Eb=72 MeV and λ0=1 μm, x rays at λ=0.12 Å (100 keV) are generated. The spectral flux, brightness, bandwidth, and pulse structure are analyzed. In the absence of filtering, the spectral bandwidth in the LSS is typically ≲1% and is limited by electron beam emittance and energy spread. Two configurations of the LSS are discussed, one providing high peak power and the other moderate average power x rays. Using present day technology, the LSS can generate picosecond pulses of x rays consisting of ≳109 photons/pulse with a peak brightness of ≳1020 photons/s mm2 mrad2 (0.1% BW) and photon energies ranging from 50 to 1200 keV.

The shower model for compact synchrotron sources and an intrinsic red-shifting mechanism

Large scale inductive electric fields can arise in regions near to or within galaxies where the density of free charges is sufficiently low. Charged particles can be accelerated to upper cosmic ray energies. A cascade pair-creation mechanism involving only electrons and synchrotron photons can produce an electron-positron plasma of the correct density and energy spectrum to account for the compact synchrotron sources with a ν −1 spectrum from centimeter to X-ray wavelengths. Radiation from such a source is highly anisotropic, causing large Doppler compression of the time intervals between source events. A large intrinsic component of red-shift can arise for emission lines (but not absorption lines) due to small angle scattering by such an electron-positron beam. The main properties of synchrotron sources can be explained.

Radio emission from bright, optically selected quasars

view Abstract Citations (105) References (78) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radio emission from bright, optically selected quasars. Condon, J. J. ; O'Dell, S. L. ; Puschell, J. J. ; Stein, W. A. Abstract In a VLA search for radio emission from 22 bright (B ≲ 17 mag), optically selected quasars, nine quasars were detected at levels exceeding 0.5 mJy at 4.885 0Hz. About two-thirds of the 22 quasars exhibit optical spectral fluxes exceeding the radio (i.e., inverted radio-to-optical spectral flux distributions αOR < 0.0) consequently, most optically selected quasars show little direct evidence for synchrotron radiation at any frequency. The detected sources span a large range in radio-to-optical luminosity ratios (from more than 10-2 down to less than l0-5) and show no clear evidence for a bimodal distribution. In addition to the radio search, 19 of the quasars were studied photometrically at infrared, optical wavelengths. No statistically significant correlation between the radio-to-optical luminosity ratio and optical properties is found, although some apparent trends are noted. Comparison of our results with previous surveys provides evidence (at the "two-sigma" level) for a dependence of this ratio upon optical properties or red shift. Several processes which might account for the radio, infrared, optical spectral flux distributions of quasars are considered. The very weak radio emission present in most optically selected quasars suggests that the infrared, optical emission from such quasars is not thermal bremsstrahlung from a source transparent at radio frequencies. Nor can the detected radio flux be thermal bremsstrahlung from the broad-line or narrow-line emission regions. Furthermore, unless a strong compact synchrotron source is hidden from view at observed radio frequencies, the infrared, optical emission cannot, in general, result from synchrotron self-Compton scattering. The observed infrared, optical radiation from blazars and OVV quasars is probably synchrotron emission, but for most quasars, other mechanisms are plausible. If the infrared, optical emission is not dependent upon the existence of a synchrotron source, then the infrared, optical and the radio emission are independent. In this case, little more can be said at present. On the other hand, if the infrared, optical radiation from quasars originates via the synchrotron mechanism (or a secondary process dependent upon synchrotron photons), the putative synchrotron source in a radio-quiet quasar must be very compact. Sufficiently compact synchrotron sources may at centimeter wavelengths be self-absorbed or free-free absorbed (by thermal gas related to the broad-line emitting regions, provided this gas covers the source). However, the absence in most quasars of strong emission at any radio frequency indicates that most quasars do not inject a copious supply of relativistic electrons into large volumes (owing, e.g., to confinement or radiative losses). Finally, purely geometrical explanations, such as the simplest relativistic jet models, seem inadequate to account for the observed distribution of radio-to-optical luminosity ratios. The relativistic jet models, in their simplest form, predict a rapid increase in the number of quasars per unit 0R (effective radio-to-optical spectral index) as αOR decreases: the observed distribution is, in fact, rather uniform in αOR. Publication: The Astrophysical Journal Pub Date: June 1981 DOI: 10.1086/158960 Bibcode: 1981ApJ...246..624C Keywords: Infrared Radiation; Quasars; Radio Emission; Synchrotron Radiation; Anisotropy; Astronomical Photometry; Infrared Astronomy; Self Absorption; Astronomy full text sources ADS | data products NED (23) SIMBAD (22)

Spontaneous formation of knots in relativistic flows - A model for variability in compact synchrotron sources

A model is proposed in which regions of enhanced synchrotron emission are formed via radiative thermal instabilities in relativistic flows. A perturbed volume in which the magnetic field is enhanced by a few tens of a percent relative to the steady value collapses due to the increased cooling rate and consequent loss in pressure. The collapse further increases the magnetic field, leading to even shorter radiative lifetimes. The instability progresses in this way until either the external electron pressure is balanced by the perturbed magnetic pressure or the overall expansion of the flow becomes important. A fluid-dynamical treatment of the instability is performed, and the results are shown to apply to flux variations and formation of knots in the relativistic flows which are thought to occur in quasars and active galactic nuclei. The knots possess the same kinematic properties as the collimated flow and can thus be responsible for the apparent superluminal motions observed in compact radio sources.

Effects of nonuniform structure on the derived physical parameters of compact synchrotron sources

The time-independent theory of a compact incoherent synchrotron radio source which contains gradients in magnetic field and in relativistic electron distribution is developed and discussed. Analytic expressions for the frequency spectrum are obtained, and we demonstrate the dependence of the spectral index below the synchrotron self-absorption turnover frequency on the gradients in the source and on the source geometry. We show that at high frequencies the existence of a gradient in the magnetic field causes a gradual bend (a steepening) in the spectrum owing to a decrease in effective source radius with increasing frequency. The theoretical interferometric fringe visibility function is computed for a nonuniform source, and it is shown that the characteristic Gaussian angular size derived from this function increases with decreasing frequency below the spectral turnover.We discuss how the important physical parameters of a nonuniform source can be directly derived from observable quantities. The results indicate that the existence of steep gradients in the magnetic field strength and/or the distribution of relativistic electrons can alleviate somewhat the energetic and inverse Compton difficulties of some compact sources, while the presence of moderate gradients only aggravates these problems relative to the homogeneous model.The theory of nonuniform components is applied tomore » the compact radio sources 1633+38 and OQ 172. We find that the radio spectrum of these objects can be interpreted as arising in simple nonuniform sources as opposed to the multiple source models that are necessary when homogeneous components are used. However, the inverse Compton optical and X-ray fluxes in the case of 1633+38 and the predicted minimum angular size in the case of OQ 172 are similar to those obtained via the uniform models.« less