scholarly journals Relativistic accretion disc reflection in AGN X-ray spectra at z = 0.5–4: a study of four Chandra Deep Fields

2020 ◽  
Vol 498 (4) ◽  
pp. 5284-5298
Author(s):  
L Baronchelli ◽  
K Nandra ◽  
J Buchner
Keyword(s):  
Signal To Noise Ratio ◽  
Accretion Disc ◽  
Data Sets ◽  
Baldwin Effect ◽  
Iron Line ◽  
X Ray ◽  
Future Data ◽  
Deep Fields ◽  
The Baldwin Effect ◽  
Best Fit

ABSTRACT We confirm that the spectra are best fit by a model containing two Compton reflection components, one from distant material, and the other displaying relativistic broadening, most likely from the inner accretion disc. The degree of relativistic broadening indicates a preference for high black hole spin, but the reflection is weaker than that expected for a flat disc illuminated by a point source. We investigate the Compton reflection signatures as a function of luminosity, redshift, and obscuration, confirming an X-ray Baldwin effect for both the narrow and broad components of the iron line. Anticorrelations are also seen with redshift and obscuring column density, but are difficult to disentangle from the Baldwin effect. Our methodology is able to extract information from multiple spectra with low signal-to-noise ratio (SN), and can be applied to future data sets such as eROSITA. We show using simulations, however, that it is necessary to apply an appropriate S/N cut to the samples to ensure the spectra add useful information.

scholarly journals The Relationship Between the Emission-Line Spectra and X-Ray/UV Continuum

1997 ◽  
Vol 159 ◽  
pp. 252-253
Author(s):  
Youjun Lu ◽  
Tinggui Wang
Keyword(s):  
Emission Line ◽  
Inverse Correlation ◽  
Baldwin Effect ◽  
Spectral Parameters ◽  
X Ray ◽  
Physical Conditions ◽  
Broad Emission ◽  
The Baldwin Effect ◽  
The Relationship ◽  
The Continuum

According to photoionization calculations, the broad emission-line (BEL) spectrum depends not only on the physical conditions of line-emitting gas, but also on the spectral shape of incident ionizing continuum, especially from the UV to X-ray. Analysis of emission-line spectra and their correlations with the continuum, therefore, provide a way of probing the anisotropy of ionizing continuum on the BLR scale, which is predicted by current models. Previous works have concentrated on explaining the Baldwin effect, an inverse correlation between equivalent width and continuum luminosity. In this contribution, we present the results of an analysis of 75 AGNs which have well-determined soft X-ray spectral parameters from ROSAT and UV line and continuum measurements.

scholarly journals The chemical composition of the accretion disc and donor star in ultra-compact X-ray binaries: A comprehensive X-ray analysis

2020 ◽  
Vol 501 (1) ◽  
pp. 548-563 ◽  
Author(s):  
Filippos Koliopanos ◽  
Mathias Péault ◽  
Georgios Vasilopoulos ◽  
Natalie Webb
Keyword(s):  
Chemical Composition ◽  
Line Strength ◽  
Accretion Disc ◽  
Accretion Discs ◽  
Type I ◽  
Iron Line ◽  
X Ray ◽  
Theoretical Predictions ◽  
History Of ◽  
X Ray Binaries

ABSTRACT We have analysed the X-ray spectra of all known Ultra-Compact X-ray Binaries (UCXBs), with the purpose of constraining the chemical composition of their accretion disc and donor star. Our investigation was focused on the presence (or absence) of the Fe Kα emission line, which was used as the probe of chemical composition of the disc, based on previously established theoretical predictions for the reflection of X-ray radiation off the surface of C/O-rich or He-rich accretion discs in UCXBs. We have contrasted the results of our spectral analysis to the history of type I X-ray bursts from these systems, which can also indicate donor star composition. We found that UCXBs with prominent and persistent iron Kα emission also featured repeat bursting activity. On the other hand, the UCXBs for which no iron line was detected, appear to have few or no type I X-ray bursts detected over more than a decade of monitoring. Based on Monte Carlo simulations, demonstrating a strong correlation between the Fe Kα line strength and the abundance of C and O in the accretion disc material and given the expected correlation between the H/He abundance and the recurrence rate of type I X-ray bursts, we propose that there is a considerable likelihood that UCXBs with persistent iron emission have He-rich donors, while those that do not, likely have C/O or O/Ne/Mg-rich donors. Our result strongly advocate for the development of more sophisticated simulations of X-ray reflection from hydrogen-poor accretion discs.

scholarly journals Emission Lines and the Spectral Energy Distributions of Quasars

1997 ◽  
Vol 159 ◽  
pp. 126-129 ◽  
Author(s):  
B.J. Wilkes ◽  
P.J. Green ◽  
S. Mathur ◽  
J.C. McDowell
Keyword(s):  
Spectral Energy Distribution ◽  
Far Infrared ◽  
Active Galaxies ◽  
Emission Lines ◽  
Spectral Energy ◽  
Baldwin Effect ◽  
Energy Distributions ◽  
X Ray ◽  
The Baldwin Effect ◽  
Initial Results

AbstractMany years of study have failed to establish conclusively relationships between a quasar’s spectral energy distribution (SED) and the emission lines it is thought to produce. This is at least partially due to the lack of well-observed SEDs. We present initial results from a line–SED study for a sample of 43 quasars and active galaxies for which we have optical and ultraviolet spectra and far-infrared–X-ray SEDs. We present the results of tests for correlations between line equivalent widths and SED luminosity and slope parameters and compare these results to those from earlier studies. We find that the Baldwin effect is weaker when the luminosity is defined close to the ionizing continuum of that line and conclude that the detailed SED is likely to be important in making further progress.

scholarly journals Black hole spin in X-ray binaries: giving uncertainties an f

2020 ◽  
Vol 500 (3) ◽  
pp. 3640-3666
Author(s):  
Greg Salvesen ◽  
Jonah M Miller
Keyword(s):  
Black Hole ◽  
Correction Factor ◽  
Accretion Disc ◽  
Iron Line ◽  
Error Budget ◽  
X Ray ◽  
Black Hole Spin ◽  
Systematic Uncertainties ◽  
Spin Measurements ◽  
X Ray Binaries

ABSTRACT The two established techniques for measuring black hole spin in X-ray binaries often yield conflicting results, which must be resolved before either method may be deemed robust. In practice, black hole spin measurements based on fitting the accretion disc continuum effectively do not marginalize over the colour-correction factor fcol. This factor parametrizes spectral hardening of the disc continuum by the disc atmosphere, whose true properties are poorly constrained. We incorporate reasonable systematic uncertainties in fcol into the eight (non-maximal) black hole spin measurements vetted by the disc continuum fitting community. In most cases, an fcol uncertainty of ±0.2–0.3 dominates the black hole spin error budget. We go on to demonstrate that plausible departures in fcol values from those adopted by the disc continuum fitting practitioners can bring the discrepant black hole spins into agreement with those from iron line modelling. Systematic uncertainties in fcol, such as the effects of strong magnetization, should be better understood before dismissing their potentially dominant impact on the black hole spin error budget.

Profile agreement indices in Rietveld and pattern-fitting analysis

1990 ◽  
Vol 23 (6) ◽  
pp. 462-468 ◽  
Author(s):  
R. J. Hill ◽  
R. X. Fischer
Keyword(s):  
Crystal Structure ◽  
Signal To Noise Ratio ◽  
Structure Refinement ◽  
Data Sets ◽  
Structure Model ◽  
Signal To Noise ◽  
Neutron Data ◽  
Reduction Stage ◽  
X Ray ◽  
Diffraction Patterns

Two definitions of profile agreement indices are now in common use for estimating the degree of fit in Rietveld refinement and in structure-independent pattern-fitting methods of powder diffraction analysis. In the original program written by Rietveld, the background was subtracted and the `non-peak' regions of the pattern were removed from further consideration in a preliminary data-reduction stage prior to Structure refinement. However, the agreement indices used in many of the more recent programs retain the background counts in the observed step intensities and include all portions of the pattern in the sums. These latter definitions are strongly dependent on the signal-to-noise ratio and on the relative amount of `background-only' regions and do not, therefore, provide a sound basis for comparing the degree of fit of peak profile and crystal structure model refinements in the general case. The extent of this dependence is illustrated quantitatively using conventional and synchrotron X-ray and constant-wavelength and time-of-flight neutron data sets with different inherent background levels and peak densities. The unweighted background-corrected peak-only profile agreement index R′ p = Σ i |Y io − Y ic|/Σ i |Y io −Y ib | (and, to a lesser extent, its weighted equivalent) is recommended as the most appropriate criterion of fit for comparative work between diffraction patterns of all kinds.

scholarly journals Disappearance of the Fe K α emission line in ultracompact X-ray binaries 4U 1543−624  and Swift J1756.9−2508

2020 ◽  
Vol 500 (4) ◽  
pp. 5603-5613
Author(s):  
Filippos Koliopanos ◽  
Georgios Vasilopoulos ◽  
Sebastien Guillot ◽  
Natalie Webb
Keyword(s):  
Accretion Disc ◽  
Spectral Shape ◽  
Continuum Emission ◽  
Spectral Parameters ◽  
Iron Line ◽  
X Ray ◽  
Upper Limits ◽  
Consistent Manner ◽  
Source Emission

ABSTRACT We investigate the long-term variability of the iron K α line in the spectra of two ultracompact X-ray sources (UCXBs) with C/O-rich donors. We revisit archival observations from five different X-ray telescopes, over an ∼20-yr period. Adopting physically motivated models for the spectral continuum, we probe the long-term evolution of the source emission in a self-consistent manner enabling physical interpretation of potential variability of the primary X-ray continuum emission and/or any emission lines from reflection off the accretion disc. We find that the spectral shape and flux of the source emission (for both objects) has remained almost constant throughout all the observations, displaying only minor variability in some spectral parameters and the source flux (largest variation is an ∼25 per cent drop in the flux of Swift J1756.9−2508). We note a striking variability of the Fe K α line that fluctuates from a notable equivalent width of ∼66–100 eV in 4U 1543−624 and ∼170 eV in Swift J1756.9−2508 , to non-detections with upper limits of 2–8 eV. We argue that the disappearance of the iron line is due to the screening of the Fe K α line by the overabundant oxygen in the C/O-rich UCXBs. This effect is cancelled when oxygen becomes fully ionized in the inner disc region, resulting in the variability of the Fe K α line in an otherwise unaltered spectral shape. This finding supports earlier predictions on the consequences of H-poor, C/O-rich accretion disc on reflection-induced fluorescent lines in the spectra of UCXBs.

scholarly journals Probing the evolution of Active Galactic Nuclei using the narrow iron Kα line

2013 ◽  
Vol 9 (S304) ◽  
pp. 148-148
Author(s):  
Claudio Ricci ◽  
S. Paltani ◽  
Y. Ueda ◽  
H. Awaki ◽  
P. Petrucci ◽  
...  
Keyword(s):  
Large Fraction ◽  
Type I ◽  
X Rays ◽  
Type Ii ◽  
Baldwin Effect ◽  
Iron Line ◽  
X Ray ◽  
Narrow Component ◽  
Line Region ◽  
Photon Index

AbstractA large fraction of the AGN output power is emitted in the X-rays, in a region very close to the supermassive black hole (SMBH). The most distinctive feature of the X-ray spectra of AGN is the iron Kα line, often observed as the superposition of a broad and a narrow component. While the broad component is found in only ~ 35–45% of bright nearby AGN, the narrow component has been found to be ubiquitous. The narrow Fe Kα line is thought to be produced in the circumnuclear material, likely in the molecular torus. Given its origin, this feature is possibly the most important tracer of neutral matter surrounding the SMBH. One of the most interesting characteristics of the narrow Fe Kα line is the decrease of its equivalent width with the continuum luminosity, the so-called X-ray Baldwin effect (Iwasawa & Taniguchi 1993). This trend has been found by many studies of large samples of type-I AGN, and very recently also in type-II AGN (Ricci et al. 2013c, submitted to ApJ). The slope of the X-ray Baldwin effect in type-II AGN is the same of their unobscured counterparts, which implies that the mechanism at work is the same. Several hypothesis have been put forward in the last decade to explain the X-ray Baldwin effect: i) a luminosity-dependent variation in the ionisation state of the iron-emitting material (Nandra et al. 1997); ii) the decrease of the number of continuum photons in the iron line region with the Eddington ratio, as an effect of the well known correlation between the photon index and the Eddington ratio (Ricci et al. 2013b, submitted to MNRAS); iii) the decrease of the covering factor of the torus with the luminosity (e.g., Page et al. 2004, Ricci et al. 2013a A&A 553, 29) as expected by luminosity-dependent unification models (e.g., Ueda et al. 2003). In my talk I will review the main characteristics of the narrow Fe K? line, and present the results of our recent works aimed at explaining the X-ray Baldwin effect using iron-line emitting physical torus models (Ricci et al. 2013a, b), and at understanding the origin of the Fe K? line (Ricci et al. 2013c). I will focus in particular on the importance of the Fe Kα line as a probe of the evolution of the physical characteristics of the molecular torus with the luminosity.

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