Scattered X-ray Photons Research Articles

Determining interstellar dust properties with scattered X-ray halo

X-ray photons, emitted by X-ray sources, are absorbed and scattered by dust grains when they travel through interstellar medium. The scattered photons within small angles result in a diffuse X-ray “halo”. Therefore, the scattered X-ray photons carry information about various properties of the dust. We study the light curves of the dust-scattered X-ray halo of Cyg X-1. Significant time lags are found between the light curves of the point source and its halo. This time lag increases with the angular distance. This can be caused by a dust concentration at 1.75 kpc from the Earth along the line of sight (LOS), with a width of ΔL = 33 pc. The time lag of Cyg X-3 also reveals a dust concentration between the point source and the Earth, and the distance of Cyg X-3 is estimated to be about 7.2 kpc. The origin of these dust concentrations is still not clearly known. Along with recent results on the dust halos of Gamma Ray Bursts (GRBs), we conclude that the dust distribution is quite nonuniform. We also study dust properties with an expanding X-ray ring from the observation of a distant GRB. The distribution of the halo photons can be used to determine the dust-radius model. Our preliminary results show that dust grain geometries may vary significantly across the Galaxy. We also propose to use the scattered X-ray halo to study the composition of the dust grains. The applicability of this method needs to be tested with advanced instruments in the future.

Vertical structure of the outer accretion disk in persistent low-mass X-ray binaries

We have investigated the influence of X-ray irradiation on the vertical structure of the outer accretion disk in low-mass X-ray binaries by performing a self-consistent calculation of the vertical structure and X-ray radiation transfer in the disk. Penetrating deep into the disk, the field of scattered X-ray photons with energy $E\gtrsim10$\,keV exerts a significant influence on the vertical structure of the accretion disk at a distance $R\gtrsim10^{10}$\,cm from the neutron star. At a distance $R\sim10^{11}$\,cm, where the total surface density in the disk reaches $\Sigma_0\sim20$\,g\,cm$^{-2}$, X-ray heating affects all layers of an optically thick disk. The X-ray heating effect is enhanced significantly in the presence of an extended atmospheric layer with a temperature $T_{atm}\sim(2\div3)\times10^6$\,K above the accretion disk. We have derived simple analytic formulas for the disk heating by scattered X-ray photons using an approximate solution of the transfer equation by the Sobolev method. This approximation has a $\gtrsim10$\,% accuracy in the range of X-ray photon energies $E<20$\,keV.

Imaging scattered x-ray radiation for measurement of local electron density in high-energy-density experiments

Imaging high-energy-density systems with scattered x-ray photons has several unique characteristics that differentiate it from the transmission radiography methods that have traditionally been used to diagnose these experiments. Because x-ray photons scatter primarily from the plasma electrons, the degree of scattering from any point in a target is roughly proportional to the electron density at that point. By constraining the directions of incident and scattered photons, the scattering event can be localized, resulting in a point-wise, internal map of the target electron density. Additionally, a scattering experiment is not restricted to the collinear source-target-detector geometry of transmission radiography. This flexibility allows for multiple detectors to image light from a single source, though potentially at different scattering angles or energy bands. Presented in this paper is the theoretical underpinning for scattered x-ray imaging, as well as a description of an upcoming proof-of-principle experiment to be conducted at the OMEGA Laser Facility.

An anomalous X-ray scattering study on glassy superionic conductor (As2Se3)1−x(CuI)x using a third-generation synchrotron radiation facility

Anomalous X-ray scattering experiments on glassy superionic conductor (As2Se3)0.4(CuI)0.6 were performed at energies close to the As, Se, and Cu K edges using a new detecting system and a third-generation synchrotron radiation facility. The detecting system was composed of a graphite-crystal energy-analyzer and a NaI(Tl) detector on a 40-cm-long arm. The overall energy resolution was about 60eV, which can discriminate the elastic signal from the fluorescence and Compton contributions, and a sufficient number of scattered X-ray photons were acquired within a reasonable data collection time. The differential structure factors, ΔiS(Q), were obtained from the detailed analyses, indicating that ΔAsS(Q) and ΔSeS(Q) are similar to those of glassy As2Se3 except at the prepeak position, and ΔCuS(Q) that in liquid CuI. From these findings, it can be concluded that a pseudo-binary mixture of the As2Se3 network matrix and CuI-related conduction pathways would be a good structural model for this superionic glass.

ACCF/AHA/HRS/SCAI Clinical Competence Statement on Physician Knowledge to Optimize Patient Safety and Image Quality in Fluoroscopically Guided Invasive Cardiovascular Procedures

ACCF/AHA/HRS/SCAI Clinical Competence Statement on Physician Knowledge to Optimize Patient Safety and Image Quality in Fluoroscopically Guided Invasive Cardiovascular Procedures

Theory of resonant elastic x-ray scattering by free molecules

A theory of resonant elastic x-ray scattering (REXS) by free molecules is presented. Different scattering channels and their interference on the formation of the spectral profile are identified. It is shown that atomiclike contributions to the cross section are totally eliminated for orthogonal orientations of the polarization vectors of the incident and scattered x-ray photons. A strong deviation from a Lorentzian profile of the spectral bands for REXS resonances is predicted. Numerical applications for the C $K$ and O $K$ spectra of carbon monoxide demonstrate the strong dependence of the spectral profile on the excitation energy and the spectral distribution of the incident radiation. Two qualitatively different contributions to the spectral shape are identified in the limit of narrow-band excitation: the first follows the excitation energy, while the second is determined by the absorption resonances. The vibrational progressions are very frequency dependent, and at large detuning frequencies the REXS cross section collapses to a single resonance with the width equal to the width of the photon function. This result is shown to hold for resonant as well as for nonresonant contributions to the REXS cross section.

Pair Cascades in Extragalactic Jets. II. The Beamed X-Ray Spectrum

view Abstract Citations (24) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Pair Cascades in Extragalactic Jets. II. The Beamed X-Ray Spectrum Levinson, Amir ; Blandford, Roger Abstract The X-ray through γ-ray emission from a relativistic jet is considered within the framework of an inhomogeneous pair-cascade model. It is shown that the overall spectrum from the model exhibits a spectral break at an energy of order (mec2)2/Eb, where Eb is the cutoff energy of the isotropic spectrum of scattered X-ray photons, above which the γ-rays are subject to significant absorption through pair production on the ambient soft radiation. Such a break has been observed thus far in the γ-ray spectra of several blazars; if blazars possess isotropic X-ray spectra similar to those observed in radio-quiet sources, then the relation between the break energy and the cutoff energy, predicted by our model, is roughly satisfied. It is argued that emission just below the γ-ray break originates near the base of the jet and is determined by the distribution function of cascading pairs there. Above the break, the slope of the emergent γ-ray spectrum reflects the radial variations of pair acceleration and soft photon intensity and should be steeper than the hard X-ray spectrum. For plausible particle acceleration prescriptions and soft radiation spectra, the characteristic hard X-ray spectra observed in some blazars are reproduced by our model. The X-ray cutoff energy is also related to the dynamics of the jet. It is argued that both the inertia and the radiative drag acting upon a jet increase sharply when the bulk Lorentz factor exceeds Γc ∼ (mec2/Eb) ∼ 10 and that jets will be accelerated up to this critical Lorentz factor which is of order that inferred from VLBI observations of superluminal radio sources. The utility of multiwaveband observations for advancing our understanding of blazars is stressed. Publication: The Astrophysical Journal Pub Date: August 1995 DOI: 10.1086/176034 Bibcode: 1995ApJ...449...86L Keywords: GALAXIES: JETS; GAMMA RAYS: THEORY; X-RAYS: GALAXIES full text sources ADS | data products SIMBAD (3) Related Materials (2) Part 1: 1995ApJ...441...79B Part 3: 1996ApJ...459..520L

Channel interference in resonance elastic x-ray scattering.

Using the one-step, scattering formulation of resonance x-ray emission, the effect of state interference on the angular distribution and polarization of molecularly scattered x-ray photons are explored. It is shown that the polarization dependence of the scattering cross sections for resonance elastic x-ray emission can be used as a crucial tool in assigning symmetries of unoccupied levels.

Monte Carlo simulation of Comptonization in plasma accreting onto neutron stars

view Abstract Citations (2) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Monte Carlo Simulation of Comptonization in Plasma Accreting onto Neutron Stars Hanawa, Tomoyuki Abstract It is shown by Monte Carlo simulation that high-energy X-rays are produced through Compton scattering in plasma accreting onto neutron stars where the gas infalls radially. The neutron star surface is heated by the gravitational energy release of the accreting gas and radiates soft X-ray photons. The X-ray from the surface are scattered by electrons in the plasma accreting onto the star. Since the infalling velocity is nearly half light speed, the energy of the scattered X-ray changes by 50 percent. Some X-rays are scattered repeatedly between the star and the accreting gas and become high-energy X-rays. The scattered X-ray photons have a power-law spectrum in high-energy range. This model is applied to X-ray spectra of type II bursts from the rapid burster MXB 1730 - 335. Publication: The Astrophysical Journal Pub Date: January 1991 DOI: 10.1086/169584 Bibcode: 1991ApJ...366..495H Keywords: Accretion Disks; Neutron Stars; Space Plasmas; Stellar Mass Accretion; Stellar Radiation; X Rays; Compton Effect; Computational Astrophysics; Monte Carlo Method; Astrophysics; RADIATION MECHANISMS; STARS: ACCRETION; STARS: NEUTRON; X-RAYS: BURSTS full text sources ADS | data products SIMBAD (2)

A model for the high-energy power-law component observed in the X-ray spectra of low-mass X-ray binaries

view Abstract Citations (12) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Model for the High-Energy Power-Law Component Observed in the X-Ray Spectra of Low-Mass X-Ray Binaries Hanawa, Tomoyuki Abstract According to recent observations, an X-ray spectrum of a low-mass X-ray binary (LMXB) is well approximated by a power-law for E greater than 10 keV when the luminosity is very low. A model is proposed for this high-energy component. In an LMXB, a neutron star accretes gas from its companion through an accretion disk. The gas accreted from the inner edge of the accretion disk has angular momentum and rotates with roughly the Keplerian velocity on the neutron star surface. X-ray photons from the neutron star are scattered in the rapidly rotating surface layer named the boundary layer. The scattered X-ray photons change their energy by the Compton effect. Some of the X-ray photons are scattered repeatedly between the boundary layer and the neutron star and observed as high-energy X-ray photons. The model reproduces the observational feature of the high-energy power-law component. The photon index of the model spectrum is expressed as a function of the model parameters. Publication: The Astrophysical Journal Pub Date: June 1990 DOI: 10.1086/168791 Bibcode: 1990ApJ...355..585H Keywords: Accretion Disks; Astronomical Models; X Ray Binaries; X Ray Spectra; Astronomical Spectroscopy; Compton Effect; Radiative Transfer; Stellar Luminosity; Stellar Mass; Astrophysics; RADIATION MECHANISMS; RADIATIVE TRANSFER; STARS: ACCRETION; STARS: NEUTRON; X-RAYS: BURSTS; X-RAYS: SPECTRA full text sources ADS | data products SIMBAD (1)

Resonant scattering in macromolecular structure research. Applications in molecular biology and material science

This report concerns the X-ray resonance scattering work carried out using the instrument X15 which receives synchrotron radiation from the storage ring DORIS. X15 covers a wavelength range from 0.6 to 3.3 Å. It therefore accesses resonance scattering at the K-absorption edges of the elements with Z = 20 (Ca) to Z = 42 (Mo) and at the L 3-absorption edges from Z = 50 (Sn) to all heavier atoms. The instrument consists of a double monochromator with a vertical offset of the beam by 1.22 m and a camera of 10 m length. A multiwire proportional chamber (from A. Gabriel) at the end of the evacuated beam line detects the scattered X-ray photons on its area 200 mm × 200 mm. The distances between sample and detector may vary in discrete steps from 0.37 m to 7.2 m. The extreme resolution in physical space from 3 Å to 3000 Å at the short and long wavelength side respectively makes X15 suitable for structure research of both low molecular weight organic compounds and macromolecular structures. Resonance X-ray scattering starts there, where the structure-resolving power of the X-ray absorption fine structure ends, i.e. at about 3 to 4 Å*. The dispersion of the resonance scattering factors f′ and f″ is strongest in the near edge region. It is also there that the chemistry of the excited atom may modify significantly the dispersion. We define the Scheme (see below). Any question of this Scheme relies on the preceding one being answered, at least experimentally (‘heard, but not fully understood’). Resonance X-ray scattering starts from the measurement of the absorption spectrum of the atom chosen as a label. The absorption spectrum does not need to be analyzed further except that it is the basis for the calculation of the resonant scattering factors f′ and″. For semicrystalline and amorphous systems described by ▪ the dispersion of the scattering intensity will be Iλ(h) = I O(h) + f′(λ)I OR(h) + {f′ 2(λ) + f″ 2(λ)}I R(h) Compare: 4b and 4a. The three basic scattering functions I O, I OR and I R λ differing in dimensions λ can be determined by measurements of I(h) at three (in practice: 20) different wavelengths in the near edge region. The cross term I OR(h) is usually most easily measured, as its dispersion function f′ (λ) differs strongly from the always predominant dispersion of the absorption and, to a smaller extent, fluorescence. Very often it is the only resonant term which can be obtained in practice. Examples are: • Iron in ferritin, dispersion of the radius of gyration of the ferritin molecules, (Stuhrmann, 1980). • Iron in hemoglobin, distances between the iron atoms of the four subunits of oxyhemoglobin, (Stuhrmann and Notbohm, 1981). • Zinc and mercury in the native and ligated Hg-derivative of ATCase (Moody). • Terbium bound to tRNA (Rigler). • Cobalt in copper (Gerstenberg). • Zinc in aluminium (Kostorz). • Distribution of ions around polyelectrolytes. Cs and I in DNA (Oberthür), Cs, Rb and Br in polyacrylic acid (Ragnetti), Cs, Ba and I in E. coli ribosomal 50S subunit (Nierhaus), binding of Ba ions to LDL and of Eu ions to DPPC vesicles (Laggner), Er in DPPC membranes (Büldt). • Bromine as a probe for the distribution of epibromhydrin in a semicrystalline copolymer PEO-epibromhydrin (Strobl, Urban). Question: Measurement of: Information: 1. Who are you? Ionization energy analytical 2. How are you? (valency, covalency) X-ray absorption near edge structure, XANES chemical range: ∼1 Å 3. What and where are your nearest neighbours? extended X-ray absorption fine structure, EXAFS chemical and structural range: ∼4 Å 4a. From excited atom to excited atoms X-ray resonance scattering in the near structural range: 4b. From excited atoms to silent atoms edge region ∼100 Å 5. From excited atom to another excited atom feeling different (different XANES) X-ray resonance scattering with more detailed dispersion analysis structural and chemical range: ∼100 Å It appears that only in the last two cases I R(h) could have been determined directly from the dispersion function f′(λ) + f″(λ). The influence of statistical and systematic errors on the results will be discussed.

Compton Scattering at the Bragg Position

With the incident "beam" provided by the standing-wave pattern which on passing the Bragg reflection range in a silicon crystal is sweeping the atomic sites, the spectrum of inelastically scattered x-ray photons has been measured for appropriately chosen scattering vectors $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}$. The results confirm the recent prediction that the spectrum is determined by the projections of the nondiagonal elements of the one-electron momentum-space density matrix $\ensuremath{\Gamma}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}|{\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}}^{\ensuremath{'}})$ on $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}$.

A simple method of X-ray fluorescence analysis in hair

A simple X-ray fluorescence (XRF) analysis method has been developed for the determination of trace element concentrations in hair. It utilises strands of hair which are dropped on a Formvar foil and irradiated in an X-ray beam. The effective sample mass was estimated by measuring scattered X-ray photons. The attenuation correction for the X-rays from light elements was estimated using a simple model. Results are in agreement with those obtained by the atomic absorption method.