Kα Fluorescence Line Research Articles

Recent results for AGN observed by the Rossi X-ray timing explorer

The Rossi X-ray Timing Explorer (RXTE) has produced many excellent observations of active galaxies, providing so far the best sensitivity over the bandpass of 10 – 20 keV. This paper reports selected RTXE data for X-ray bright Seyfert galaxies in the context of the currently popular models. One is the recent result for two Seyfert 1 galaxies, NGC 5548 and IC 4329a: both show the “canonical” Seyfert 1 X-ray spectra, with an underlying power law, plus iron Kα fluorescence line and Compton reflection. Interestingly, in both cases, the profile of the Fe K line does not extend as far to the red as seen in the famous MCG-6-30-15, and this indicates that the regions where the Fe K lines originate in AGN are diverse. Independently, in both objects we see a strong spectral variability of the primary continua, which soften as the sources brighten. The second result is for the heavily absorbed Seyfert 2 NGC 4945. The RXTE data confirm the strong absorption corresponding to the optical depth to electron scattering of about 2, but also reveal rapid variability of the hard (8 – 30 keV) X-ray emission on a time scale of a day or less. This suggests that for NGC 4945, the putative parsec-size molecular torus cannot be both geometrically and optically thick. It also implies that if the Cosmic X-ray Background is made up of heavily absorbed sources, they are unlikely to have the absorber confined to a geometrically thin disk as inferred for NGC 4945.

Detecting Compton Reflection and a Broad Iron Line in MCG −5‐23‐16 withRXTE

We report the detection with the Rossi X-Ray Timing Explorer (RXTE) of a Compton reflection signature in the Seyfert galaxy MCG -5-23-16. RXTE also resolves the Fe Kα fluorescence line with FWHM ~48,000 km s-1. This measurement provides the first independent confirmation of ASCA detections in Seyfert galaxies of broad Fe Kα lines that are thought to be the signature of emission from the inner regions of an accretion disk orbiting a black hole. Under the assumption that reflection arises from an isotropic source located above a neutral accretion disk, and using a theoretical model that accounts for the dependence of the reflected spectrum on inclination angle, we derive a 90% confidence range for the disk inclination of i = 50°-81°. The large inclination is consistent with that expected from the unified model for MCG -5-23-16 based on its Seyfert 1.9 classification. If we assume that the high-energy cutoff in the incident spectrum lies at energies larger than a few hundred keV, then the equivalent width of the Fe Kα line is much larger than predicted for the amount of reflection. This implies either an enhanced iron abundance, a covering factor of reflecting material cf > 0.5, or a cutoff in the incident spectrum at energies between ~60 and ~200 keV.

Self‐consistent Thermal Accretion Disk Corona Models for Compact Objects. II. Application to Cygnus X‐1

We apply our self-consistent accretion disk corona (ADC) model, with two different geometries, to the broadband X-ray spectrum of the black hole candidate Cygnus X-1. As shown in a companion paper, models in which the Comptonizing medium is a slab surrounding the cold accretion disk cannot have a temperature higher than about 140 keV for optical depths greater than 0.2, resulting in spectra that are much softer than the observed 10-30 keV spectrum of Cyg X-1. In addition, the slab-geometry models predict a substantial soft excess at low energies, a feature not observed for Cyg X-1, and Fe Kα fluorescence lines that are stronger than observed. Previous Comptonization models in the literature have invoked a slab geometry with optical depth τT 0.3 and coronal temperature Tc ~ 150 keV, but they are not self-consistent. Therefore, ADC models with a slab geometry are not appropriate for explaining the X-ray spectrum of Cyg X-1. Models with a spherical corona and an exterior disk, however, predict much higher self-consistent coronal temperatures than the slab-geometry models. The higher coronal temperatures are due to the lower amount of reprocessing of coronal radiation in the accretion disk, giving rise to a lower Compton cooling rate. Therefore, for the sphere-plus-disk geometry, the predicted spectrum can be hard enough to describe the observed X-ray continuum of Cyg X-1 while predicting Fe fluorescence lines having an equivalent width of ~40 eV. Our best-fit parameter values for the sphere-plus-disk geometry are τT ≈ 1.5 and Tc ≈ 90 keV.

Iron Kα Evidence for Two X‐Ray Reprocessors in MCG −5‐23‐16

We report a remarkable Fe Kα fluorescence line profile in the Seyfert 1.9 galaxy MCG -5-23-16. The line is complex, consisting of a narrow core located at the galaxy's systemic velocity and wings to the red and blue sides of the core. This represents only the second detection with ASCA of an Fe Kα line profile with significant broadening blueward of 6.4 keV, consistent with Doppler boosting. The line core has an EW of ~60 eV and the wings have a combined EW of ~200 eV. The entire profile cannot be easily modeled with an emission line predicted from standard accretion disk theories. Instead, the line is marginally triple-peaked and is best described with three Gaussians having rest energies of 5.37+ 0.23−0.19 keV (FWHM = 30,200 km s-1), 6.37 ± 0.04 keV (FWHM < 6,600 km s-1), and 6.58+ 0.35−0.38 keV (FWHM = 75,300 km s-1). The line can also be modeled with a narrow Gaussian at ~6.4 keV and an emission line from an accretion disk viewed at an inclination angle of ~30° to 65°, depending on the ionization state of the gas. Within the context of the unified model, the most likely physical description of the complex profile is a superposition of an emission line from an accretion disk and a line that arises far from the disk in either the obscuring torus or the broad line region. This represents the first strong evidence for emission from two distinct X-ray reprocessors within a single Seyfert 1-type galaxy.

The iron K response in an X-ray illuminated relativistic disc and a black hole mass estimate

A method is proposed for the estimate of the black hole mass in an active galactic nucleus which is based on the response of the intensity, centroid energy and width of the iron Kα fluorescence line to variations of the ionizing continuum. The method is illustrated for the case of a geometrically thin and optically thick, X-ray illuminated disk, in Keplerian rotation around a Schwarzschild black hole, using a detailed model of the line emissivity. This method is complementary to the one that makes use of variations in detailed line profiles, and could be applied also to measurements obtained at moderate energy resolution.

Influence of chemical combination on K-fluorescence lines of compounds of Al, Si and S

This paper extends earlier work on the shift on the Kα-fluorescence line of sulphur, which is due to the chemical environment of the atom, and shows that similar good agreement between theory and experiment is also found for Si and Al. On the other hand the Kβ-transitions, which directly involve the lectrons engaged in chemical bonding, cannot properly be described by any such monocentric model. Finally the chemical shift of the Kα line of an atom is shown to depend very strongly on the polarity of the bonds to this atom, and also on the d-character of the bonding.

X-ray fluorescence line shift of some phosphorus compounds

A simple X-ray technique is described for the study of phosphorus Kα fluorescent line shift as a measure of the state of chemical combination of the phosphorus atom, using commercially available equipment. Illustrations are given for various types of phosphorus compounds and their Kα line positions. The Kα lines for various phosphorus compounds are found to shift towards shorter wavelengths (higher energy) if the atom is bonded to a greater number of atoms or to more electro-negative atoms.