Strong Relativistic Effects Research Articles

X-ray reflection in the Seyfert galaxy 1H 0419−577 revealing strong relativistic effects in the vicinity of a Kerr black hole

We report results obtained from six XMM-Newton observations of the Seyfert galaxy 1H 0419-577. The source was observed in a wide range of different flux levels, allowing its long-term spectral variability to be studied in detail, as already reported recently by Pounds et al. Here we show that the X-ray spectrum is well described by a simple two-component model comprising a power law with constant spectral shape and variable normalization, and a much more constant ionized reflection component from the inner accretion disc, which carries the signature of strong relativistic effects. One of the observations was performed when the source was in a particularly low-flux state in which the X-ray spectrum is rather peculiar and exhibits a very flat hard spectrum (with spectral index close to 1 in the 2-10 keV band), with broad residuals below 6.6 keV (rest frame) and a steep soft excess below about 1 keV. We interpret the spectrum as being reflection-dominated by X-ray reprocessed emission from the inner accretion disc. The primary continuum, which illuminates the disc, is almost completely unobserved, possibly because of strong light bending towards the central supermassive black hole. The ionized reflection model simultaneously accounts for the broad hard residuals and hard flat spectrum and for the soft excess. The same model provides an excellent description of the data at all the other flux levels, the most important difference being a variation in the power-law normalization. Our spectral decomposition and interpretation of the spectral variability implies that most of the X-ray emission in this source originates from within a few gravitational radii from the central black hole and requires that the compact object is almost maximally spinning.

X-ray reverberation studies of AGN

The broad iron line seen in the X-ray spectra of Active Galactic Nuclei (AGN) is a unique probe of the very near environment of the black hole where strong field general relativistic effects are important. The iron fluorescence line is produced when the X-ray continuum emission, which originates in the accretion disk corona, back-scatters or “reflects” off the disk. The line is sensitive to Doppler, transverse Doppler shifts and special relativistic boosting from the motion of the disk and gravitational redshifting from being deep in the potential well of the black hole. The sudden activation of X-ray flares in the corona (the presence of which are suggested by observation) provides a variable illumination pattern over the disk, and the reflected “echo” from these flares can be used to map out the astrophysics of this region in detail. This is the technique of reverberation mapping.

Chemical investigation of hassium (element 108).

The periodic table provides a classification of the chemical properties of the elements. But for the heaviest elements, the transactinides, this role of the periodic table reaches its limits because increasingly strong relativistic effects on the valence electron shells can induce deviations from known trends in chemical properties. In the case of the first two transactinides, elements 104 and 105, relativistic effects do indeed influence their chemical properties, whereas elements 106 and 107 both behave as expected from their position within the periodic table. Here we report the chemical separation and characterization of only seven detected atoms of element 108 (hassium, Hs), which were generated as isotopes (269)Hs (refs 8, 9) and (270)Hs (ref. 10) in the fusion reaction between (26)Mg and (248)Cm. The hassium atoms are immediately oxidized to a highly volatile oxide, presumably HsO(4), for which we determine an enthalpy of adsorption on our detector surface that is comparable to the adsorption enthalpy determined under identical conditions for the osmium oxide OsO(4). These results provide evidence that the chemical properties of hassium and its lighter homologue osmium are similar, thus confirming that hassium exhibits properties as expected from its position in group 8 of the periodic table.

Epicyclic Orbital Oscillations in Newton's and Einstein's Dynamics

We apply Feynman's principle, “The same equations have the same solutions”, to Kepler's problem and show that Newton's dynamics in a properly curved 3-D space is identical with that described by Einstein's theory in the 3-D optical geometry of Schwarzschild's spacetime. For this reason, rather unexpectedly, Newton's formulae for Kepler's problem, in the case of nearly circular motion in a static, spherically spherical gravitational potential accurately describe strong field general relativistic effects, in particular vanishing of the radial epicyclic frequency at r = r ms.

Adsorption of CO on cluster models of platinum (111): A four-component relativistic density-functional approach

We report on results of a theoretical study of the adsorption process of a single carbon oxide molecule on a Platinum (111) surface. A four-component relativistic density functional method was applied to account for a proper description of the strong relativistic effects. A limited number of atoms in the framework of a cluster approach is used to describe the surface. Different adsorption sites are investigated. We found that CO is preferably adsorbed at the top position.

The strength and width of Fe K lines in Seyferts and their correlations with the X-ray slope

We study properties of Fe K lines of a large sample of Seyfert 1s observed by ASCA. Fits with power laws and Gaussian lines yield the average linewidth and equivalent width of 0.22±0.03 keV and 0.13±0.01 keV, respectively. Thus, the typical lines are weak and narrow. We then obtain the average line profile of all our spectra, and find it to consist of a narrow core and blue and red wings, with the red wing being much weaker than that of e.g. MCG −6-30-15. We obtain three average spectra of Seyferts grouped according to the hardness, and find the equivalent width of the core (originating in a remote medium) to be ≃50 eV in all three cases. The wings are well fitted by a broad line from a disc with strong relativistic effects. Its equivalent width correlates with the slope, increasing from ∼70 eV for the hardest spectrum to ∼120 eV for the softest one. The inner disc radius decreases correspondingly from ∼40 to ∼10 gravitational radii, and the fitted disc inclination is ∼45°. The obtained correlation between the slope and the strength of the broad Fe K line is found to be consistent with the previously found correlation of the slope and Compton reflection.

Dielectronic Recombination and Spectroscopy of the Heaviest Li-like Ions

Dielectronic recombination (DR) of very heavy Li-like ions including Pb79+, Bi80+, and U89+ with Δn = 0 core excitations (1s22s1/2 → 1s22p1/2,3/2) has been investigated at the electron cooler of the Experimental Storage Ring (ESR) of GSI in Darmstadt, Germany. Absolute rate coefficients and resonance energies of DR via intermediate doubly excited Rydberg states 1s22p1/2 nℓ (n ≥ 20) and doubly excited states 1s22p3/2nℓj (n = 6 for Pb79+ and Bi80+, and n = 5 for U89+) of recombined Be-like ions have been determined. For the 1s22p1/2 nℓ series Rydberg states up to n ≈ 50 were resolved in the measurement. In addition individual fine structure components of the Rydberg resonances can clearly be distinguished. For the first time in such a heavy system the series limit has directly been observed in DR. For these very heavy ions strong relativistic effects as well as the Breit interaction have to be taken into account in order to explain the experimental findings. The experimental data are compared with fully relativistic multi configuration Dirac Fock (DR/MCDF) calculations

Atomic and Electronic Structures and Dynamics in Liquid Alloys near Eutectic Point

Electronic structures and dynamics in liquid alloy Sn x Pb 100- x near the eutectic point ( x =73.9) are studied in the first-principles molecular dynamics. Position of the first peak in the calculated partial radial distribution function agrees with the experimental one for pure liquid metals while its height and shape suggest more disordered local structures. No appreciable segregation of particular elements is observed. The electronic structure is essentially metallic with separated s - and p -bands, which are characteristic in heavy group-IV elements with strong relativistic effects on the valence electrons. Bond charge indicative of the covalent nature of the electronic states is found in a snapshot of the valence charge density but a life time of such bonding is at most several tenths of psec, which is of the order of magnitude of the atomic vibrations.

The evidence against Comptonization as a mechanism to explain the Fe Kα line profile in MCG-6-30-15

It has recently been suggested that Compton down-scattering may give rise to the broad iron Kα line seen in the X-ray spectrum of the Seyfert 1 galaxy MCG-6-30-15. This model suggests that the Comptonizing optically thick plasma surrounding the central X-ray source has a temperature of 0.5keV and a large radius of 1014cm. This offers an alternative to the standard model whereby the broadening of the iron line is solely the result of strong general relativistic effects. We revise the Comptonization model and show that statistically the disc-line model gives a much better fit to the time average of the data analysed by Iwasawa et al. in 1996 and 1999. We also demonstrate that the Comptonization model has problems with simultaneous fitting of the redshifted tail and the core of the line. We show that, in the case of the 1996 data, the best-fitting Thomson depth τ∼1.6 is consistent with the lack of continuum break, which is constrained to be at photon energies E≳100keV. However, the total amount of power in the UV component required to cool the Comptonizing cloud exceeds the Eddington limit. For large black hole masses relativistic effects are important and for small masses the Eddington limit is exceeded by a larger factor. In the case of the 1999 data, the best-fitting Thomson depth is τ∼5.7; this would imply the existence of a break in the continuum at E∼16keV, which is not observed. (However, we point out that the down-scattering break may be diluted if a fraction of the continuum is observed directly.) This rules out Comptonization as the principal mechanism to explain the shape of the Fe Kα line in MCG-6-30-15.

Faceting and stress of missing-row reconstructed transition-metal (110) surfaces

We present ab initio total energy and stress calculations for the unreconstructed and $(2\ifmmode\times\else\texttimes\fi{}1)$--missing-row reconstructed Ir (110) and Rh (110) surfaces. We then use those results to set up a model rationalizing the $(2\ifmmode\times\else\texttimes\fi{}1)$ reconstruction as a faceting transition to a long-wavelength--corrugated (111)-like surface. Next, we discuss the qualitative extension of such model to a general $n\ifmmode\times\else\texttimes\fi{}1$ reconstruction, using ab initio results, elasticity theory, and classical dynamics simulations for Al (110). Remarkably, despite the severe inherent limitations of the model, the $3\ifmmode\times\else\texttimes\fi{}1$ structure is found to be the most stable for Ir. Finally, we use the stress density to analyze the stress increase upon reconstruction, and find it to be due to a changed balance of tensile and compressive contributions in the near-surface region, which closely matches previous interpretations of the reconstruction mechanism. We conclude that, as for the (100) surface, the reconstruction basically originates from the strong relativistic contraction effects on the electronic structure of end-of-series $5d$ metals.

The electronic structure of MoC and WC by anion photoelectron spectroscopy

Photoelectron spectra of MoC− and WC− are reported at two detachment energies, 532 and 355 nm. The electron affinities of MoC and WC were measured to be 1.358 (0.010) and 1.022 (0.010) eV, respectively. Seven low-lying electronic states were observed for MoC within 2 eV above its ground state whereas six were observed for WC within 2.4 eV above its ground state. The bonding and spectroscopy of MoC and WC were found to be different and were attributed to their different atomic configurations due to the strong relativistic effects in W. The current study reports the first spectroscopic information on WC.

Astrophysical evidence for massive black holes

Massive black holes have long been thought as the most plausible “engine” for bright active galaxies. However, strong independent evidence for the existence of such exotic objects was lacking. This situation has changed dramatically in the past three years with the appearance of new evidence for very massive compact objects in nearby galaxies, and with the possible detection of strong relativistic effects expected near a black hole. Furthermore, it now appears that a massive black hole may exist at the nuclei of most galaxies. Higher quality observations expected in the next few years, may significantly strengthen the case for massive black holes.

Relativistic effects on the4p-5sexcitations of krypton

Generalized oscillator strengths of krypton for ${4p}^{6}{(}^{1}{S}_{0})\ensuremath{\rightarrow}{4p}^{5}{(}^{2}{P}_{3/2,1/2})5s$ are calculated in the first Born approximation at a self-consistent-field level with Dirac-Fock, Dirac-Slater, Hartree-Fock, and Hartree-Slater wave functions. Strong relativistic effects are noticed. The estimate of relaxation on a single-electron matrix element suggests the necessity of a Dirac-Fock multiconfiguration calculation for the excitations.

Can a Relativistic Iron K Line Be Resolved in Cyg X-1 withSIXA?

Broad, asymmetric iron K lines have been detected in the x-ray spectra of abouta dozen Active Galactic Nuclei (AGN). The distorted line profiles are most probablydue to strong relativistic effects in the innermost parts of an optically thickaccretion disk around a central black hole. However, none of the Galactic BlackHole Candidates (GBHC) has exhibited any clear evidence of a relativistic ironline profile. Observations of the persistently bright black hole candidate Cyg X-1have only revealed a narrow Gaussian line. Weak relativistic features may nothave been detected due to insufficient signal-to-noise and energy resolution.We present simulated observations of a relativistic iron K line in the spectrumof Cyg X-1 obtained with SIXA onboard SPECTRUM-RÖNTGEN-GAMMA.We studied the feasibility of detecting the relativistic effects in the line profileboth in the hard and soft state of the source. Our results show that a relativisticline profile can be resolved in Cyg X-1 within a 50–100 ksec observation if theaccretion disk extends within ~ 100 rg from the compact object and the equivalent width of the relativistic component exceeds ~ 30–40 eV.

ROSAT monitoring of persistent giant and rapid variability in the narrow-line Seyfert 1 galaxy IRAS 13224-3809

We report evidence for persistent giant and rapid X-ray variability in the radio-quiet, ultrasoft, strong Fe II, narrow-line Seyfert 1 galaxy IRAS 13224-3809. Within a 30 day ROSAT High Resolution Imager (HRI) monitoring observation at least five giant amplitude count rate variations are visible, with the maximum observed amplitude of variability being about a factor of 60. We detect a rise by a factor of about 57 in just two days. IRAS 13224-3809 appears to be the most X-ray variable Seyfert known, and its variability is probably nonlinear. We carefully check the identification of the highly variable X-ray source with the distant galaxy, and it appears to be secure. We examine possible explanations for the giant variability. Unusually strong relativistic effects and partial covering by occulting structures on an accretion disc can provide plausible explanations of the X-ray data, and we explore these two scenarios. Relativistic boosting effects may be relevant to understanding the strong X-ray variability of some steep spectrum Seyferts more generally.

Chemical properties of element 106 (seaborgium)

The synthesis, via nuclear fusion reactions, of elements heavier than the actinides, allows one to probe the limits of the periodic table as a means of classifying the elements. In particular, deviations in the periodicity of chemical properties for the heaviest elements are predicted as a consequence of increasingly strong relativistic effects on the electronic shell structure1,2,3,4,5,6,7. The transactinide elements have now been extended up to element 112 (ref. 8), but the chemical properties have been investigated only for the first two of the transactinide elements, 104 and 105 (refs 9,10,11,12,13,14,15,16,17,18,19). Those studies showed that relativistic effect render these two elements chemically different from their lighter homologues in the same columns of the periodic table (Fig. 1). Here we report the chemical separation of element 106 (seaborgium, Sg) and investigations of its chemical behaviour in the gas phase and in aqueous solution. The methods that we use are able to probe the reactivity of individual atoms, and based on the detection of just seven atoms of seaborgium we find that it exhibits properties characteristic of the group 6 homologues molybdenum and tungsten. Thus seaborgium appears to restore the trends of the periodic table disrupted by relativistic effects in elements 104 and 105.

Density Functional Study of N2 Activation by Molybdenum(III) Complexes. Unusually Strong Relativistic Effects in 4d Metal Compounds

All-electron generalized-gradient density functional (DF) calculations have been carried out on both the nonrelativistic and relativistic levels to address the mechanism of N2 cleavage by L3Mo(III) complexes. The reaction features computed for the model reactants with L = NH2, NMe2, and Me are compared to the recently published values for the (H2N)3Mo derivative obtained with the help of the effective core potential (ECP) DF method and to the experimental data reported for the reaction of N2 with (RArN)3Mo (R = C(CD3)2CH3, Ar = 3,5-C6H3Me2). Despite a qualitative agreement between the reaction parameters of the present relativistic and the previous ECP DF calculations, some important quantitative differences are found, like a lower activation barrier by more than 10 kJ mol-1 and a higher overall reaction exothermicity by about 80 kJ mol-1. The influence of the electronic and steric properties of the ligands L on the parameters of the cleavage reaction has been analyzed. The Mo(III) trialkyl complexes, at ...

Narrow‐line Seyfert 1 galaxies

AbstractThis paper summarizes the soft X‐ray properties of narrow‐line Seyfert 1 galaxies (NLS1). NLS1 have generally steeper soft X‐ray continuum slopes than Seyfert 1s with broader lines, and there exists an anticorrelation between 0.1–2.4 keV continuum slope and the FWHM of the Hβ line. Objects with steep 0.1–2.4 keV continuum slopes and Hβ FWHM > 3000 km s−1 are clearly discriminated against by nature. When simple power‐law models are fit to the data, photon indices reach values up to about 5, much higher than is usually seen in Seyfert 1s. Models with smaller mass black holes and/or higher Eddington fractions show some promise to explain the relation between the FWHM of the Hβ line and the X‐ray continuum slope. We further report evidence for persistent gaint and rapid variability in the ultrasoft narrow‐line Seyfert 1 galaxy IRAS 13224–3809. We have examined possible explanations for the gaint variability. Unusually strong relativistic effects provide a plausible explanation of the X‐ray data. Relativistic boosting effects may be relevant to understanding the strong X‐ray variability of some steep spectrum Seyferts more generally.

Relativistic effects exhibited by the generalized Stokes parameters for electron impact excitation of quasi one-electron atoms

The generalized Stokes parameters are an extension of the regular Stokes parameters by considering spin-polarized incident electrons. We have derived relationships between the generalized Stokes parameters in the non-relativistic fine-structure approximation. Relativistic effects in the intermediate energy range are due to spin - orbit coupling. These effects are masked when averaging over the electron spin polarization for the regular Stokes parameters, but are very prominent for the generalized Stokes parameters. We have considered quasi one-electron atoms and have found that Rb, Cs, Cu, Ag and Au exhibit strong relativistic effects, while K shows weaker effects and Na almost none at all. The experimental testing of these effects can complement those which are exhibited by the generalized STU parameters.

Photoionisation process in the 5d, 6s and 6p shells of atomic lead and the 4d shell of atomic tin

Photoionisation processes in the 5d, 6s and 6p shells of atomic lead and the 4d shell of atomic tin have been investigated. Of interest were the occurrence of individual photoelectron lines as a consequence of electron correlation and relativistic effects, and the angular distribution of dominant lines in these spectra. The analysis of the experimental data shows that the 6s photoelectron spectrum of Pb is governed in the jj coupling model by initial-state configuration-interaction effects which explain the occurrence and the asymmetry parameter beta of individual lines. The same effects play a role in the 5d photoelectron spectrum, but here final ionic state configuration interaction is of equal importance. Based on these mechanisms of a complete interpretation of the 5d photoelectron spectrum of Pb is given. Surprisingly, the 4d photoelectron spectrum of Sn exhibits nearly identical structure. The asymmetry parameter beta for two 5d photoelectron lines is not yet understood; it requires a calculation which takes into account the strong correlation and relativistic effects. The asymmetry parameter beta for the 6p1/2 photoelectron line does not agree with the theoretical prediction of the relativistic Dirac-Slater calculation of Manson and co-workers (1982).