Showing papers on "Synchrotron radiation published in 2001"

SPECTRA: a synchrotron radiation calculation code.

Abstract: An application program to calculate various characteristics of synchrotron radiation, called SPECTRA, is described. The program does not need any other commercial software and is equipped with a full graphical user interface which makes data input quite easy. Equations on synchrotron radiation from arbitrary-field sources in a near-field region are derived, as are simplified expressions for ideal devices using a far-field approximation. Effective numerical methods implemented in SPECTRA to reduce computation time are explained, and several examples are presented.

The Generation of Nonthermal Particles in the Relativistic Magnetic Reconnection of Pair Plasmas

Abstract: Particle acceleration in the magnetic reconnection of electron-positron plasmas is studied by using a particle-in-cell simulation. It is found that a significantly large number of nonthermal particles are generated by the inductive electric fields around an X-type neutral line when the reconnection outflow velocity, which is known to be an Alfven velocity, is on the order of the speed of light. In such a relativistic reconnection regime, we also find that electrons and positrons form a power-law-like energy distribution through their drift along the reconnection electric field under the relativistic Speiser motion. A brief discussion of the relevance of these results to the current sheet structure, which has an antiparallel magnetic field in astrophysical sources of synchrotron radiation, is presented.

Resolution limits for infrared microspectroscopy explored with synchrotron radiation

Abstract: The spatial resolution for infrared microspectroscopy is investigated to determine the practical limits imposed by diffraction or optical aberrations. Quantitative results are obtained using high brightness synchrotron radiation, which serves as a diffraction-limited infrared “point source” for the microscope. The measured resolving power is in good agreement with diffraction theory, including a ∼ 30% improvement for a confocal optical arrangement. The diffraction calculation also shows how the confocal setup leads to better image contrast. The full width at half maximum of the instrument’s resolution pattern is approximately λ/2 for this arrangement. One achieves this diffraction limit when the instrument’s apertures define a region having dimensions equal to the wavelength of interest. While commercial microspectrometers are well corrected for optical aberrations (allowing diffraction-limited results), the standard substrates used for supporting specimens introduce chromatic aberrations. An analysis of ...

Chandra X-Ray Observations of Pictor A: High-Energy Cosmic Rays in a Radio Galaxy

Abstract: We report X-ray observations of the nearby, powerful radio galaxy Pictor A with the Chandra Observatory and optical and near-UV observations of its western radio hot spot with the Hubble Space Telescope. X-ray emission is detected from the nucleus, a 19 (110 kpc) long jet to the west of the nucleus, the western radio hot spot some 42 (240 kpc) from the nucleus, and the eastern radio lobe. The morphology of the western hot spot is remarkably similar to that seen at radio and optical wavelengths, where the emission is known to be synchrotron radiation. The X-ray spectrum of the hot spot is well described by an absorbed power law with photon index Γ = 2.07 ± 0.11. The X-ray jet coincides with a weak radio jet and is laterally extended by 20 (1.9 kpc). The observed jet is up to 15 times brighter in X-rays than any counterjet, a difference ascribed to relativistic boosting since the western radio lobe is probably the closer. The jet's spectrum is well modeled by an absorbed power law with Γ = 1.94 and poorly fitted by a Raymond-Smith thermal plasma model. The emission processes responsible for the X-rays are discussed in detail. The radio-to-optical spectrum of the hot spot breaks or turns down at 1013-1014 Hz, and its X-ray spectrum is not a simple extension of the radio-to-optical spectrum to higher frequencies. Thermal models for the hot spot's X-ray emission are ruled out. Synchrotron self-Compton models involving scattering from the known population of electrons give the wrong spectral index for the hot spot's X-ray emission and are also excluded. A composite synchrotron plus synchrotron self-Compton model can match the X-ray observations but requires similar contributions from the two components in the Chandra band. We show that the hot spot's X-ray emission could be synchrotron self-Compton emission from a hitherto unobserved population of electrons emitting at low radio frequencies but do not favor this model in view of the very weak magnetic field required. An inverse Compton model of the jet, in which it scatters microwave background photons but moves nonrelativistically, requires a magnetic field a factor of 30 below equipartition and ad hoc conditions to explain why the radio lobes are fainter than the jet in X-rays but brighter in the radio. These problems are alleviated if the jet moves relativistically, but models with an equipartition field require an implausibly small angle (θ) between the jet and the line of sight. A model with θ 23° and a field a factor of 6 below equipartition seems viable. Synchrotron radiation is an alternative process for the X-ray emission. The expected synchrotron spectrum from relativistic electrons accelerated by strong shocks and subject to synchrotron radiation losses is in very good agreement with that observed for both the hot spot and jet. The possibility that the relativistic electrons result via photopion production by high-energy protons accelerated in shocks (a proton-induced cascade) is briefly discussed.

Modeling the Low-State Spectrum of the X-Ray Nova XTE J1118+480

Abstract: Based on recent multiwavelength observations of the new X-ray nova XTE J1118+480, we can place strong constraints on the geometry of the accretion flow in which a low/hard-state spectrum, characteristic of an accreting black hole binary, is produced. We argue that the absence of any soft blackbody-like component in the X-ray band implies the existence of an extended hot optically thin region, with the optically thick cool disk truncated at some radius Rtr 55RSchw. We show that such a model can indeed reproduce the main features of the observed spectrum: the relatively high optical to X-ray ratio, the sharp downturn in the far-UV band, and the hard X-ray spectrum. The absence of the disk blackbody component also underscores the requirement that the seed photons for thermal Comptonization be produced locally in the hot flow, e.g., via synchrotron radiation. We attribute the observed spectral break at 2 keV to absorption in a warm, partially ionized gas.

Astronomical sources of circularly polarized light and the origin of homochirality.

Abstract: Possible astronomical sources of ultraviolet circularly polarized light(UVCPL) which might be responsible for enantiomeric selection in interstellarorganic molecules are considered, Synchrotron radiation from magnetic neutronstars has been suggested as a possible source of UVCPL However, synchrotronradiation in these situations is not predicted to be strongly circularlypolarized Very few such sources show optical synchrotron radiation and in thefew that do circular polarization has not been observed Magnetic white dwarfsand white dwarf binaries (Polars) can be highly circularly polarized but anyeffect on molecular clouds and star formation regions must rely on rare chance encounters Recent observations show that substantial levels of circularpolarization are present in reflection nebulae in star formation regions Thismechanism produces polarized light exactly when and where it is needed inregions where star formation is occurring and organic molecules are known to be present

Microspectroscopy and imaging using a delay line detector in time-of-flight photoemission microscopy

Abstract: A method for microspectroscopy and energy-selective imaging using a special photoemission electron microscope (PEEM) is presented. A modified commercial PEEM was combined with a delay line device as x, y, t detector serving as the basic arrangement for spectromicroscopy. One can measure the time of flight of the electrons passing a drift section in order to analyze the energy distribution of photoelectrons in PEEM. The time of flight is referenced to the time structure of the synchrotron radiation from an electron storage ring. At electron kinetic energies of less than 20 eV within the drift region a spatial resolution of about 100 nm has been obtained. Fast counting electronics (instead of a camera) delivers an image for real-time monitoring on an oscilloscope screen or for image acquisition by a computer. A time resolution of about 500 ps has been obtained with the potential of further improvement. The spatial resolution of the delay line detector is about 50 μm in the image plane corresponding to 1000 ...

Chandra X-ray Imaging and Spectroscopy of the M87 Jet and Nucleus

Abstract: We report X-ray imaging spectroscopy of the jet of M87 at subarcsecond resolution with the Chandra X-ray Observatory. The galaxy nucleus and all the knots seen at radio and optical wavelengths, as far from the nucleus as knot C, are detected in the X-ray observations. There is a strong trend for the ratio of X-ray-to-radio, or optical, flux to decline with increasing distance from the nucleus. At least three knots are displaced from their radio/optical counterparts, being tens of parsecs closer to the nucleus at X-ray than at radio or optical wavelengths. The X-ray spectra of the nucleus and knots are well described by power laws absorbed by cold gas, with only the unresolved nucleus exhibiting intrinsic absorption. In view of the similar spectra of the nucleus and jet knots, and the high X-ray flux of the knots closest to the nucleus, we suggest that the X-ray emission coincident with the nucleus may actually originate from the parsec- or subparsec-scale jet rather than the accretion disk. Arguments are given that the X-ray emission process is unlikely to be inverse Compton scattering. Instead, we favor synchrotron radiation. Plotted as νSν, the spectra of the knots generally peak in or just above the optical-near-infrared band. However, the overall spectra of at least three knots cannot be described by simple models in which the spectral index monotonically increases with frequency, as would result from synchrotron losses or a high-energy cut-off to the injected electron spectrum. Instead, these spectra must turn down just above the optical band and then flatten in the X-ray band. In the context of a synchrotron model, this result suggests that either the X-ray-emitting electrons/positrons in these knots represent a separate "population" from those that emit the radio and optical radiation or that the magnetic field is highly inhomogeneous. If the former interpretation is correct, our results provide further support for the notion that radio galaxies produce a hard [γ 2-2.5, N(E) ∝ E-γ] spectrum of high-energy [ ~ 107-108] electrons and possibly positrons.

A horizontal two-axis diffractometer for high-energy X-ray diffraction using synchrotron radiation on bending magnet beamline BL04B2 at SPring-8

Abstract: A horizontal two-axis diffractometer for glasses and liquids, installed at SPring-8 bending magnet beamline BL04B2, operated at 8 GeV electron energy, is described. Photon energies of 37.8 and 61.7 keV were obtained using a bent Si (1 1 1) crystal and a bent Si (2 2 0) crystal, respectively. The instrument has been successfully applied to measure diffraction spectra of vitreous SiO 2 in transmission geometry up to scattering vector Q =36 A −1 , and measured total structure factor S ( Q ) was well reproduced by reverse Monte Carlo modelling.

Chandra Observations of the X-Ray Jet of 3C 273

Abstract: We report results from Chandra observations of the X-ray jet of 3C 273 during the calibration phase in 2000 January. The zeroth-order images and spectra from two 40 ks exposures with the High-Energy Transmission Grating and Low-Energy Transmission Grating + Advanced CCD Imaging Spectrometer-S show a complex X-ray structure. The brightest optical knots are detected and resolved in the 0.2-8 keV energy band. The X-ray morphology tracks well the optical. However, while the X-ray brightness decreases along the jet, the outer parts of the jet tend to be increasingly bright with increasing wavelength. The spectral energy distributions of four selected regions can best be explained by the inverse Compton scattering of (beamed) cosmic microwave background photons. The model parameters are compatible with equipartition and a moderate Doppler factor, which is consistent with the one-sidedness of the jet. Alternative models either imply implausible physical conditions and energetics (the synchrotron self-Compton model) or are sufficiently ad hoc to be unconstrained by the present data (synchrotron radiation from a spatially or temporally distinct particle population).

Chandra Observations of the X-Ray Jet of 3C273

Abstract: We report results from Chandra observations of the X-ray jet of 3C~273 during the calibration phase in 2000 January. The zeroeth-order images and spectra from two 40-ks exposures with the HETG and LETG+ACIS-S show a complex X-ray structure. The brightest optical knots are detected and resolved in the 0.2-8 keV energy band. The X-ray morphology tracks well the optical. However, while the X-ray brightness decreases along the jet, the outer parts of the jet tend to be increasingly bright with increasing wavelength. The spectral energy distributions of four selected regions can best be explained by inverse Compton scattering of (beamed) cosmic microwave background photons. The model parameters are compatible with equipartition and a moderate Doppler factor, which is consistent with the one-sidedness of the jet. Alternative models either imply implausible physical conditions and energetics (the synchrotron self-Compton model) or are sufficiently ad hoc to be unconstrained by the present data (synchrotron radiation from a spatially or temporally distinct particle population).

Cosmic-ray positrons from mature gamma-ray pulsars

Abstract: We consider a possible contribution of mature γ -ray pulsars (with ages of yrs) to cosmic ray positrons. Within the framework of the γ -ray pulsar outer gap model, pairs in the pulsar magnetosphere are produced by the cascade of pairs through synchrotron radiation of the return current from the outer gap. A good fraction of these cascade pairs are reflected by the hard X-rays from the polar cap via resonant scattering and escape from the pulsar through the light cylinder. The escaped pairs are accelerated to relativistic energies in the pulsar wind driven by low-frequency electromagnetic waves. Using Monte Carlo simulations, we generate a sample of the mature γ -ray pulsars in our Galaxy and calculate the positron production rate from these pulsars. In a simple "leaky box" model, we calculate the ratio of cosmic-ray positrons to total electrons. Our result indicates that the pulsar contribution to the cosmic ray positrons peaks at about 60 GeV and the observed ratio can be explained in this model.

BACH, the beamline for advanced dichroic and scattering experiments at ELETTRA

Abstract: A beamline for advanced dichroism (BACH), to perform light polarization dependent experiments in the 35–1600 eV photon energy range is under construction at the ELETTRA Synchrotron Radiation Source in Trieste, Italy. The radiation source, based on two APPLE-II helical undulators, is designed for high photon flux and high resolving powers. The photons dispersion system is based on a Padmore variable angle spherical grating monochromator with a typical resolving power of 20 000–6000, 20 000–6000, and 15 000–5000 in the energy ranges 35–200 eV, 200–500 eV, and 500–1600 eV, respectively. Two separate branches after the monochromator allow setting two independent experimental chambers. The photon flux in the experimental chamber(s), calculated at the best resolutions achievable and with the aperture of the slits set at 10 μm, is expected to be above 1011 photons’s with linearly or circularly polarized light. In addition, a fourth grating operates in the 400–1600 eV range to provide a higher flux, 1012 photons’...

The elliptically polarized undulator beamlines at BESSY II

Abstract: During 1998/99 three beamlines of the UE56-PGM type were built at BESSY-II to meet the increased need for synchrotron radiation of tuneable, i.e. linear to fully circular, polarization. We report on the results of characterization measurements, which were focused on spectral resolution, photon flux and polarization properties. The spectral resolution for all three beamlines exceeds E=DE ¼100 000 at 64.1 eV as obtained from absorption spectra of doubly excited He. The flux measurements resulted in values that closely follow the theoretical prediction of up to 1 � 10 14 photons/(s 100 mA 0.1%) at 160 eV. The degree of polarization turned out to be close to 100% with circular and linear content, each of up to 100% depending on the undulator shift value, as predicted by theory. We also give first results on the double beam mode in which both undulator modules produce horizontally separated beams. This mode was used for fast switching of the polarization, utilizing a motorized chopper in the beamline. # 2001 Published by Elsevier Science B.V.

Measurement of the x-ray mass attenuation coefficient of copper using 8.85-20 keV synchrotron radiation

Abstract: This work presents the x-ray extended range technique for measuring x-ray mass attenuation coefficients. This technique includes the use of multiple foil attenuators at each energy investigated, allowing independent tests of detector linearity and of the harmonic contributions to the monochromated synchrotron beam. Measurements over a wide energy range allow the uncertainty of local foil thickness to be minimized by the calibration of thin sample measurements to those of thick samples. The use of an extended criterion for sample thickness selection allows direct determination of dominant systematics, with an improvement of accuracies compared to previous measurements by up to factors of 20. Resulting accuracies for attenuation coefficients of copper ~8.84 to 20 keV! are 0.27‐0.5 %, with reproducibility of 0.02%. We also extract the imaginary component of the form factor from the data with the same accuracy. Results are compared to theoretical calculations near and away from the absorption edge. The accuracy challenges available theoretical calculations, and observed discrepancies of 10% between current theory and experiments can now be addressed.

Construction of laser-heated diamond anvil cell system for in situ x-ray diffraction study at SPring-8

Abstract: A double-sided laser heated diamond anvil cell (DAC) system was constructed at a high brilliance, undulator beamline (BL10XU) at SPring-8 a third generation synchrotron radiation facility, for performing in situ angle-dispersive x-ray diffraction experiments under high temperature and high pressure. The design of this system puts emphasis on reliable data collection for the structural analysis. With this system, the adjustment of the optical systems for both x-ray and laser beams can be done easily, and high quality diffraction data can be obtained typically within several minutes. A system for temperature measurement of ten points in a sample area at the same time was also developed. The performance of the laser heated DAC system was tested by observing phase transitions of natural olivine.

High-accuracy EUV metrology of PTB using synchrotron radiation

Abstract: The development of EUV lithography, has made high-accuracy at-wavelength metrology necessary. Radiometry using synchrotron radiation has been performed by the German national metrology institute, the Physikalisch-Technische Bundesanstalt (PTB), for almost 20 years. Recently, PTB has set up four new beamlines for EUV metrology at the electron storage ring BESSY II. At a bending magnet, a monochromator for soft X-ray radiometry is routinely used for reflectometry and detector characterisation. A reflectometer designed for mirrors up to 550 mm in diameter and 50 kg in mass will be operational in January 2002. Detector characterisation is based on a primary detector standard, a cryogenic electrical substitution radiometer. Measuring tools for EUV source characterisation are calibrated on this basis. Detector testing at irradiation levels comparable to the anticipated conditions in EUV tools is feasible at a plane grating monochromator, installed at an undulator optimised for EUV radiation. A test beamline for EUV optics alignment and system metrology has been installed, using undispersed undulator radiation. Bending magnet radiation is available at a station for irradiation testing. A focusing mirror collects a radiant power of about 10 mW within the multilayer bandwidth and a 1 mm² focal spot.

Characterization of the transverse coherence of hard synchrotron radiation by intensity interferometry.

Abstract: The transverse coherence of x rays was measured with an intensity interferometer using a 120-microeV-bandwidth monochromator operating at 14.41 keV. By analyzing the transverse coherence profiles, a vertical source profile of a 25-m long undulator of SPring-8, as well as the coherence degradation by a phase object in the beam path, were quantitatively characterized.

Damping of relativistic electron beams by synchrotron radiation

Abstract: Relativistic electrons emit synchrotron radiation due to their gyro- and guiding-center motions in a curved magnetic field. In this article, the kinetic theory of relativistic electron beams is developed to account for radiation reaction by including the Abraham–Lorentz reaction force in the kinetic equation. As an application of this theory, the dynamics of runaway electrons is examined and a steady-state solution is constructed describing a balance between acceleration by the electric field, pitch-angle scattering, and radiation reaction. Furthermore, it is found that a beam of relativistic electrons can be slowed down by the combined effects of pitch-angle scattering and radiation reaction. This damping can be more efficient than ordinary collisional drag, and appears to explain the decay of post-disruption runaway currents in the Joint European Torus (JET) [R. D. Gill, Nucl. Fusion 33, 1613 (1993)].

Measurement of detection efficiency and response functions for an Si(Li) x-ray spectrometer in the range 0.1-5 keV

Abstract: Efficiency and response functions were determined for a modern commercial energy-dispersive x-ray spectrometer in the photon energy range 0.1–5 keV using dispersed and undispersed synchrotron radiation. The spectrometer was equipped with an Si(Li) detector crystal, a thin-film window and a digital pulse processor. Monochromatized synchrotron radiation from the PTB VUV radiometry beamline at the electron storage ring BESSY was used for the absolute determination of the detection efficiency with a typical relative uncertainty of 1–2% in the photon energy range 0.1–1.5 keV by direct comparison with calibrated photodiodes. At higher photon energies, the efficiency was found by comparison of the measured and calculated undispersed synchrotron radiation spectrum. The absolute intensity of the synchrotron radiation was known with a relative uncertainty of less than 1%. In the overlapping region, the results from the two independent experiments are in full agreement. The energy dependence of the measured efficiency can be explained only with a detector model assuming that there is no dead layer. A simple model for the effect of incomplete charge collection (ICC) was applied to describe the measured response functions. Consequences of the ICC such as broadening and shift of low-energy peaks and redistribution of counts around 1.84 keV are explained with the model, in accordance with the experimental results. Copyright © 2001 John Wiley & Sons, Ltd.

HST optical spectral index map of the jet of 3C 273

Abstract: We present HST images at 622 nm and 300 nm of the jet in 3C273 and determine the run of the optical spectral index at 0.2" along the jet. The smoothness of spectral index changes shows that the physical conditions are varying smoothly across the jet. There is no correlation between the optical flux and spectral index, as would be expected for relativistic electrons suffering strong cooling due to synchrotron emission. We find no evidence for localized acceleration or loss sites. This suggests that the spectral shape is not changing much throughout the jet. We show that relativistic beaming and/or sub-equipartition magnetic fields cannot remove the discrepancy between light-travel time along the jet and the lifetime of electrons emitting optical synchrotron radiation. We consider this further evidence in favour of a distributed electron acceleration process.

The versatility of collimated plane grating monochromators

Abstract: In the last few years monochromator development at the German synchrotron radiation facility BESSY II improved conventional monochromator designs, especially the SX700 design, considerably. It was possible to convert the high brilliance of undulator radiation at third generation synchrotron sources very successfully into outstanding monochromator performance in terms of high energy resolution, photon flux and focus size. New mechanical designs and precise control of the angular settings of optical elements resulted in very high monochromator stability and allowed even for an absolute energy calibration of monochromators. This report reviews the design principles of collimated plane grating monochromators and presents results obtained within the first two years of BESSY II operation.

Feasibility study of online high-spatial-resolution MOSFET dosimetry in static and pulsed x-ray radiation fields

Abstract: Improvements have been made in the measurement of dose profiles in several types of X-ray beams. These include 120-kVp X-ray beams from an orthovoltage X-ray machine, 6-MV Bremsstrahlung from a medical LINAC in conformal mode and the 50-200 keV energy spectrum of microbeams produced at the medical beamline station of the European Synchrotron Radiation Facility. Using a quadruple metal-oxide-semiconductor field-effect transistor (MOSFET) sensor chip in "edge on" mode together with a newly developed sensor readout system, the feasibility of online scanning of the profiles of quasi-static and pulsed radiation beams was demonstrated. Measurements of synchrotron pulsed microbeams showed that a micrometer-scale spatial resolution was achievable. The use of several MOSFETs on the same chip gave rise to the correction of misalignments of the oxide films of the sensor with respect to the microbeam, ensuring that the excellent spatial resolution of the MOSFET used in "edge-on" mode was fully utilized.

Gamma-ray bursts from unstable Poynting-dominated outflows

Abstract: Poynting-flux driven outflows from magnetized rotators are a plausible explanation for gamma-ray burst engines. We suggest a new possibility for how such outflows might transfer energy into radiating particles. We argue that, in a region near the rotation axis, the Poynting flux drives non-linearly unstable large-amplitude electromagnetic waves (LAEMW) that ‘break’ at radii where the MHD approximation becomes inapplicable. In the ‘foaming’ (relativistically reconnecting) regions formed during the wave breaks, the random electric fields stochastically accelerate particles to ultrarelativistic energies which then radiate in turbulent electromagnetic fields. The typical energy of the emitted photons is a fraction of the fundamental Compton energy with plus additional boosting due to the bulk motion of the medium. The emission properties are similar to synchrotron radiation, with a typical cooling time ∼10−3 s. During the wave break, the plasma is also bulk accelerated in the outward radial direction and at larger radii can produce afterglows due to interactions with the external medium. The near equipartition fields required by afterglow models may be due to magnetic field regeneration in the outflowing plasma (similar to field generation by LAEMW in laser–plasma interactions) and mixing with the upstream plasma.

Submicron focusing of hard x rays with reflecting surfaces at the ESRF

Abstract: We describe Kirkpatrick-Baez (KB) reflecting mirror systems that have been developed at the European Synchrotron Radiation Facility (ESRF). They are intended to be used mainly in the hard x-ray domain from 10 KeV to 30 KeV for microfluorescence, microdiffraction and projection microscopy applications. At 19 KeV a full width at half maximum (FWHM) spot size of 200x600 nanometers has been measured and with an estimated irradiance gain of 3.5x105. The alignment and bending processes of the system are automated based on the wavefront information obtained by sequentially scanning slits and reading a position-sensitive device located in the focal plane. The sub-microradian sensitivity of this method allows us to predict the spot size and ot provide a metrology map of the surfaces for future improvements of the performances. A novel device based on specular reflection by a micromachined platinum mirror has been used to determine the spot size with an equivalent slit size of less than 100 nanometers. Projection phase images of submicron structures are presented which clearly show both the high potential and also the present limitations of the system. First microfluorescence images obtained at 20.6 KeV are shown. Finally, a roadmap towards diffraction-limited performance with metal and multilayer surfaces is presented.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.