Fe Line Profile Research Articles

X-Ray Fluorescence from Super-Eddington Accreting Black Holes

Abstract X-ray reverberation has proven to be a powerful tool capable of probing the innermost region of accretion disks around compact objects. Current theoretical effort generally assumes that the disk is geometrically thin, optically thick, and orbiting with Keplerian speed. Thus, these models cannot be applied to systems where super-Eddington accretion happens because the thin disk approximation fails in this accretion regime. Furthermore, state-of-the-art numerical simulations show that optically thick winds are launched from the super-Eddington accretion disks, thereby changing the reflection geometry significantly from the thin disk picture. We carry out theoretical investigations on this topic by focusing on the Fe Kα fluorescent lines produced from super-Eddington disks, and show that their line profiles are shaped by the funnel geometry and wind acceleration. We also systematically compare the Fe line profiles from super-Eddington thick disks to those from thin disks, and find that the former are substantially more blueshifted and symmetric in shape. These results are consistent with the observed Fe Kα line from the jetted tidal disruption event, Swift J1644, in which a transient super-Eddington accretion disk was formed out of stellar debris. Therefore, careful analysis of the Fe Kα line profile can be used to identify systems undergoing super-Eddington accretion.

Red-skewed Kα iron lines in GX 13+1

Context. Broad, asymmetric, and red-skewed Fe Kα emission lines have been observed in the spectra of low-mass X-ray binaries hosting neutron stars (NSs) as a compact object. Because more than one model is able to describe these features, the explanation of where and how the red-skewed Fe lines are produced is still a matter of discussion. It is broadly accepted that the shape of the Fe Kα line is strongly determined by the special and general relativistic effects occurring in the innermost part of the accretion disk. In this relativistic framework, the Fe fluorescent lines are produced in the innermost part of the accretion disk by reflection of hard X-ray photons coming from the central source (corona and/or NS surface). We developed an alternative and nonrelativistic model, called the WINDLINE model, that is capable to describe the Fe line features. In this nonrelativistic framework, the line photons are produced at the bottom of a partly ionized outflow (wind) shell as a result of illumination by the continuum photons coming from the central source. In this model the red-skewness of the line profile is explained by repeated electron scattering of the photons in a diverging outflow. Aims. Examining the asymmetry of the fluorescent Fe K emission line evident in the XMM-Newton EPIC-pn spectra of the NS source GX 13+1, we aim to distinguish between the two line models. Because GX 13+1 is a well-known disk-wind source, it is a perfect target for testing the WINDLINE model and compare the spectral fits between the relativistic and nonrelativistic line models. Methods. We used two XMM-Newton EPIC-pn observations in which the Fe line profiles were previously reported in the literature. These observations are not strongly affected by pile-up, and the Fe emission lines appear very strong and red-skewed. In order to access the goodness of the fit and distinguish between the two line models, we used the run-test statistical method in addition to the canonical χ2 statistical method. Results. The DISKLINE and WINDLINE models both fit the asymmetric Fe line well that is present in the XMM-Newton energy spectra of GX 13+1. From a statistical point of view, for the two observations we analyzed, the run-test was not able to distinguish between the two Fe line models, at 5% significance level.

Truncation of the Accretion Disk at One-third of the Eddington Limit in the Neutron Star Low-mass X-Ray Binary Aquila X-1

Abstract We perform a reflection study on a new observation of the neutron star (NS) low-mass X-ray binary Aquila X-1 taken with NuSTAR during the 2016 August outburst and compare with the 2014 July outburst. The source was captured at ∼32% L Edd, which is over four times more luminous than the previous observation during the 2014 outburst. Both observations exhibit a broadened Fe line profile. Through reflection modeling, we determine that the inner disk is truncated (where R g = GM/c 2) and (errors quoted at the 90% confidence level). Fiducial NS parameters (M NS = 1.4 M ⊙, R NS = 10 km) give a stellar radius of R NS = 4.85 R g ; our measurements rule out a disk extending to that radius at more than the 6σ level of confidence. We are able to place an upper limit on the magnetic field strength of B ≤ 3.0–4.5 × 109 G at the magnetic poles, assuming that the disk is truncated at the magnetospheric radius in each case. This is consistent with previous estimates of the magnetic field strength for Aquila X-1. However, if the magnetosphere is not responsible for truncating the disk prior to the NS surface, we estimate a boundary layer with a maximum extent of and . Additionally, we compare the magnetic field strength inferred from the Fe line profile of Aquila X-1 and other NS low-mass X-ray binaries to known accreting millisecond X-ray pulsars.

Understanding the cochlear implant environment by mapping perilymph proteomes from different species.

Cochlear implants operate within a bony channel of the cochlea, bathed in a fluid known as the perilymph. The perilymph is a complex fluid containing ions and proteins, which are known to actively interact with metallic electrodes. To improve our understanding of how cochlear implant performance varies in preclinical in vivo studies in comparison to human trials and patient outcomes, the protein composition (or perilymph proteome) is needed. Samples of perilymph were gathered from feline and guinea pig subjects and analyzed using liquid chromatography with tandem mass spectrometry (LC-MS/MS) to produce proteomes and compare against the recently published human proteome. Over 64% of the proteins in the guinea pig proteome were found to be common to the human proteome. The proportions of apolipoproteins, enzymes and immunoglobulins showed little variation between the two proteomes, with other classes showing similarity. This establishes a good basis for comparison of results. The results for the feline profile showed less similarity with the human proteome and would not provide a quality comparison. This work highlights the suitability of the guinea pig to model the biological environment of the human cochlear and the need to carefully select models of the biological environment of a cochlear implant to more adequately translate in vitro and in vivo studies to the clinic.

Gravitational lensing size scales for quasars

AbstractWe review results from our monitoring observations of several lensed quasars performed in the optical, UV, and X‐ray bands. Modeling of the multi‐wavelength light curves provides constraints on the extent of the optical, UV, and X‐ray emission regions. One of the important results of our analysis is that the optical sizes as inferred from the microlensing analysis are significantly larger than those predicted by the theoretical‐thin‐disk estimate. In a few cases we also constrain the slope of the size‐wavelength relation. Our size constraints of the soft and hard X‐ray emission regions of quasars indicate that in some objects of our sample the hard X‐ray emission region is more compact than the soft and in others the soft emission region is smaller. This difference may be the result of the relative strengths of the disk‐reflected (harder and extended) versus corona‐direct (softer and compact) components in the quasars of our sample. Finally, we present the analysis of several strong microlensing events where we detect an evolution of the relativistic Fe line profile as the magnification caustic traverses the accretion disk. These caustic crossings are used to provide constraints on the innermost stable circular orbit (ISCO) radius and the accretion disk inclination angle of the black hole in quasar RX J1131–1231. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Three-dimensional non-LTE radiative transfer effects in Fe I lines

In network and active region plages, the magnetic field is concentrated into structures often described as flux tubes (FTs) and sheets (FSs). 3-D radiative transfer (RT) is important for energy transport in these concentrations. It is also expected to be important for diagnostic purposes but has rarely been applied for that purpose. Using true 3-D, non-LTE (NLTE) RT in FT/FS models, we compute Fe line profiles commonly used to diagnose the Sun's magnetic field by comparing the results with those obtained from LTE/1-D (1.5-D) NLTE calculations. Employing a multilevel iron atom, we study the influence of basic parameters such as Wilson depression, wall thickness, radius/width, thermal stratification or magnetic field strength on all Stokes $I$ parameters in the thin-tube approximation. The use of different levels of approximations of RT may lead to considerable differences in profile shapes, intensity contrasts, equivalent widths, and the determination of magnetic field strengths. In particular, LTE, which often provides a good approach in planar 1-D atmospheres, is a poor approximation in our flux sheet model for some of the most important diagnostic Fe I lines (524.7nm, 525.0nm, 630.1nm, and 630.2nm). The observed effects depend on parameters such as the height of line formation, field strength, and internal temperature stratification. Differences between the profile shapes may lead to errors in the determination of magnetic fields on the order of 10 to 20%, while errors in the determined temperature can reach 300-400K. The empirical FT models NET and PLA turn out to minimize the effects of 3D RT, so that results obtained with these models by applying LTE may also remain valid for 3-D NLTE calculations. Finally, horizontal RT is found to only insignificantly smear out structures such as the optically thick walls of FTs and FSs, allowing features as narrow as 10km to remain visible.

REVEALING THE STRUCTURE OF AN ACCRETION DISK THROUGH ENERGY-DEPENDENT X-RAY MICROLENSING

We present results from monitoring observations of the gravitationally lensed quasar RX J1131-1231 performed with the Chandra X-ray Observatory. The X-ray observations were planned with relatively long exposures that allowed a search for energy-dependent microlensing in the soft (0.2-2 keV) and hard (2-10 keV) light curves of the images of RX J1131-1231. We detect significant microlensing in the X-ray light-curves of images A and D, and energy-dependent microlensing of image D. The magnification of the soft band appears to be larger than that in the hard band by a factor of ~ 1.3 when image D becomes more magnified. This can be explained by the difference between a compact, softer-spectrum corona that is producing a more extended, harder spectrum reflection component off the disk. This is supported by the evolution of the fluorescent iron line in image D over three consecutive time-averaged phases of the light curve. In the first period, a Fe line at E = 6.36(-0.16,+0.13) keV is detected (at > 99% confidence). In the second period, two Fe lines are detected, one at E = 5.47(-0.08,+0.06) keV (detected at > 99% confidence) and another at E = 6.02(-0.07,+0.09) keV (marginally detected at > 90% confidence), and in the third period, a broadened Fe line at 6.42(-0.15,+0.19) keV is detected (at > 99% confidence). This evolution of the Fe line profile during the microlensing event is consistent with the line distortion expected when a caustic passes over the inner disk where the shape of the fluorescent Fe line is distorted by General Relativistic and Doppler effects.

General relativistic models of the X-ray spectral variability of MCG–6-30-15

We study in detail the GR models of the X-ray spectral variability for various geometries of the X-ray source and with various relativistic effects being the dominant cause of spectral variability. The predicted properties are compared with the Suzaku observational data of the Seyfert 1 galaxy MCG--6-30-15. The data disfavor models with the X-ray source (1) moving vertically on the symmetry axis or (2) corotating with the disc and changing height not far above the disc surface. The most likely explanation for the observed variability is given by the model involving the X-ray source located at a very small, varying distance from a rapidly rotating black hole. This model predicts some enhanced variations in the red wing of the Fe line, which are not seen in the Suzaku observations. However, the enhanced variability of the red wing, while ruled out by the Suzaku data, is consistent with an excess RMS variability, between 5 and 6 keV, reported for some previous ASCA and XMM observations. We speculate that the presence or lack of such a feature is related to the change of the ionization state of the innermost part of the disc, however, investigation of such effects is currently not possible in our model (where a neutral disc is assumed). If the model, completed by description of ionization effects, proves to be fully consistent with the observational data, it will provide a strong indication that the central black hole in MCG--6-30-15 rotates rapidly, supporting similar conclusions derived from the Fe line profile.

ASUZAKUOBSERVATION OF NGC 4593: ILLUMINATING THE TRUNCATED DISK

We report results from a 2007 Suzaku observation of the Seyfert 1 AGN NGC 4593. The narrow Fe K alpha emission line has a FWHM width ~4000 km/s, indicating emission from >~ 5000 Rg. There is no evidence for a relativistically broadened Fe K line, consistent with the presence of a radiatively efficient outer disk which is truncated or transitions to an interior radiatively inefficient flow. The Suzaku observation caught the source in a low-flux state; compared to a 2002 XMM observation, the hard X-ray flux decreased by 3.6, while the Fe K alpha line intensity and width each roughly halved. Two model-dependent explanations for the changes in Fe line profile are explored. In one, the Fe line width has decreased from ~10000 to ~4000 km/s from 2002 to 2007, suggesting that the thin disk truncation/transition radius has increased from 1000-2000 to >~5000 Rg. However, there are indications from other compact accreting systems that such truncation radii tend to be associated only with accretion rates relative to Eddington much lower than that of NGC 4593. In the second (preferred) model, the line profile in the XMM observation consists of a time-invariant narrow component plus a broad component originating from the inner part of the truncated disk (~300 Rg) which has responded to the drop in continuum flux. The Compton reflection component strength R is ~1.1, consistent with the measured Fe K alpha line total EQW with an Fe abundance 1.7 times solar. The modest soft excess has fallen by a factor of ~20 from 2002 to 2007, ruling out emission from a region 5 lt-yr in size.

A COMPREHENSIVE X-RAY SPECTRAL ANALYSIS OF THE SEYFERT 1.5 NGC 3227

We present results of a 100 ks XMM observation of the Seyfert 1.5 NGC 3227. Our best-fit broadband model to the pn spectrum consists of a moderately flat (photon index 1.57) hard X-ray power-law absorbed by cold gas with N_H = 3 * 10^21 cm^-2, plus a strong soft excess, modeled as a steep power law with a photon index of 3.35, absorbed by cold gas with N_H = 9 * 10^20 cm^-2. The soft excess normalization increases by ~20% in ~20 ks, independently of the hard X-ray component, and the UV continuum, tracked via the OM, also shows a strong increasing trend over the observation, consistent with reprocessing of soft X-ray emission. Warm absorber signatures are evident in both the EPIC and RGS; we model two layers, with log(xi) = 1.2 and 2.9 erg cm s^-1, and with similar column densities (~1-2 * 10^21 cm^-2). The outflow velocities relative to systemic of the high- and low-ionization absorbers are estimated to be -(2060(+240,-170)) km/s and -(420(+430,-190)) km/s, respectively. The Fe K alpha line width FWHM is 7000 +/- 1500 km/s; its inferred radius is consistent with the BLR and with the inner radius of the dust reverberation-mapped by Suganuma et al. An emission feature near 6.0 keV is modeled equally well as a narrow redshifted Fe K line, possibly associated with a disk "hot-spot," or as the red wing to a relativistically broadened Fe line profile. Swift-BAT and archival RXTE data suggest at most weak Compton reflection (R <~ 0.5), and a high-energy cutoff near 100 keV. From RXTE monitoring, we find tentative evidence for a significant fraction of the Fe line flux to track continuum variations on time scales < 700 days.

Observational effects of the Kerr metric

Strong gravity effects should have crucial impact on structure and radiative properties of an accretion flow surrounding a black hole. We discuss several observational consequences of such effects. (i) We note that the hard X-ray spectra of Seyfert galaxies, which appear to be intrinsically harder when observed at higher inclination angles, may be most naturally explained by radiative properties of plasmas in the Kerr metric. (ii) We indicate bending of photon trajectories to the equatorial plane, which is a distinct property of rapidly rotating black holes, as the most feasible effect underlying reduced variability of the Fe Kα line observed in several objects. (iii) Both the extreme Fe line profile and the variability pattern (observed, e.g., in a Seyfert galaxy MCG–6-30-15) independently indicate that a primary hard X-ray source must be located within a few gravitational radii from the Kerr black hole. We indicate a hot inner corona as the most likely model of such a source.

Accretion Disk Illumination in Schwarzschild and Kerr Geometries: Fitting Formulae

We describe the methodology and compute the illumination of geometrically thin accretion disks around black holes of arbitrary spin parameter $a$ exposed to the radiation of a point-like, isotropic source at arbitrary height above the disk on its symmetry axis. We then provide analytic fitting formulae for the illumination as a function of the source height $h$ and the black hole angular momentum $a$. We find that for a source on the disk symmetry axis and $h/M > 3$, the main effect of the parameter $a$ is allowing the disk to extend to smaller radii (approaching $r/M \to 1$ as $a/M \to 1$) and thus allow the illumination of regions of much higher rotational velocity and redshift. We also compute the illumination profiles for anisotropic emission associated with the motion of the source relative to the accretion disk and present the fractions of photons absorbed by the black hole, intercepted by the disk or escaping to infinity for both isotropic and anisotropic emission for $a/M=0$ and $a/M=0.99$. As the anisotropy (of a source approaching the disk) increases the illumination profile reduces (approximately) to a single power-law, whose index, $q$, because of absorption of the beamed photons by the black hole, saturates to a value no higher than $q \gtrsim 3$. Finally, we compute the fluorescence Fe line profiles associated with the specific illumination and compare them among various cases.

Fe emission and ionized excess absorption in the luminous quasar 3C 109 with XMM-Newton

We report results from an XMM-Newton observation of the broad-line radio galaxy 3C 109 (z=0.3056). Previous ASCA data revealed the presence of a broad iron line from the accretion disc with which the XMM-Newton spectrum is fully consistent. However, although improving the ASCA constraints on the line parameters, the quality of the data is not high enough to distinguish between an untruncated accretion disc extending down to small radii close to the black hole and a scenario in which the innermost 20-30 gravitational radii are missing. For this reason, our results are model-dependent and the hard data can be modeled equally well by considering an absorption scenario in which a large column of neutral gas partially covers the X-ray continuum source. However, the absorber would have to comprise hundreds/thousands very compact clouds close to the X-ray source, which seems rather extreme a requirement. The 2-10 keV intrinsic luminosity of 3C 109 is of the order of 2-3 x 10{sup 45} erg s{sup -1} regardless of the adopted model. A recent black hole mass estimate of {approx} 2 x 10{sup 8} M{sub {circle_dot}} implies that L{sub bol}/L{sub Edd} > 1. If partial covering is excluded, the observed reflection fraction (of the order of unity), steep photon index (1.86), and Fe line equivalent width (about 100 eV) all suggest to exclude that the X-ray continuum is strongly beamed indicating that the large Eddington ratio is associated with a radiatively efficient accretion process and making it unlikely that the innermost accretion disc is replaced by a thick radiatively inefficient medium such as in advection-dominated accretion models. We also confirm previous findings on the detection of low energy absorption in excess of the Galactic value, where we find excellent agreement with previous results obtained in X-rays and at other wavelengths (optical and infrared). The better quality of the XMM-Newton data enables us to attribute the excess absorption to slightly ionized gas in the line of sight, located at the redshift of 3C 109. The most likely interpretation for the excess absorption is that the line-of-sight is grazing the obscuring torus of unified models, which is consistent with the inclination inferred from the Fe line profile (about 40{sup o}) and with the hybrid radio-galaxy/quasar nature of 3C 109.

SS 433: results of a recent multiwavelength campaign

We conducted a multiwavelength campaign in 2002 September-October, to observe SS 433. We used the Giant Meter Radio Telescope for radio observations, the Physical Research Laboratory Infrared Telescope at Mt Abu for infrared (IR), the ARIES telescope at Nainital for optical photometry, the telescope at the Vainu Bappu observatory for spectral measurements and the Rossi X-ray Timing Explorer for X-ray observations. We find sharp variations in intensity on time-scales of a few minutes in the X-ray, IR and radio wavelengths. Differential photometry in the IR observations clearly indicates significant intrinsic variations on short time-scales of minutes throughout the campaign. Combining the results for these wavelengths, we find a signature of delay of about two days between the IR and radio signals. The X-ray spectrum yielded double Fe line profiles which corresponded to red and blue components of the relativistic jet. We also present the broad-band spectrum averaged over the campaign duration.

BeppoSAXobservations of the quasar Markarian 205

We present the first BeppoSAX observation (0.1 to 220 keV) of the quasar Mrk 205. We have searched for the unusual Fe line profile observed in the XMM-Newton spectrum which has been widely discussed in the recent literature. We find no evidence for a broad, ionized Fe line component in our data. We detect for the first time a Compton hump in this object. When this component is included in the fit, the line strength diminishes, in agreement with a recent re-analysis of the XMM-Newton data, but with better constraints on the reflection component thanks to the PDS instrument (15-220 keV). We interpret this fact as another indication for illumination of distant, cold material rather than reprocessing in the highly ionized inner part of an accretion disk. We cannot constrain the presence of a high energy cutoff but we confirm the existence of a variable soft excess (one year time scale).

BeppoSAX observations of the quasar Markarian 205

We present the first BeppoSAX observation (0.1 to 220 keV) of the quasar Mrk 205. We have searched for the unusual Fe line profile claimed in the XMM-Newton spectrum which has been widely discussed in recent literature. We find no evidence for a broad, ionized Fe line component in our data. We detect for the first time a Compton hump in this object. Besides, when this component is included in the fit, the line strength diminishes, in agreement with a recent re-analysis of the XMM-Newton data, but with better constraints on the reflection component thanks to the PDS instrument (15-220 keV). We interpret this fact as another indication for illumination of a distant and cold material rather than reprocessing in the highly ionized inner parts of an accretion disk. We cannot constrain the presence of a high energy cutoff but we confirm the existence of a variable soft excess (one year timescale).

On the Origin of Broad Fe Kα and HiHα Lines in Active Galactic Nuclei

We examine the properties of the Fe emission lines that arise near 6.4 keV in the ASCA spectra of AGNs. Our emphasis is on the Seyfert 1 galaxies where broad and apparently complex Fe Kα emission is observed. We consider various origins for the line but focus on the pros and cons for line-emitting accretion disk models. We develop a simple model of an illuminated disk capable of producing both X-ray and optical lines. The model is able to reproduce the observed Fe Kα FWHM ratio as well as the radii of maximum emissivity implied by the profile redshifts. The overall profile shapes, however, do not fit well the predictions of our disk illumination model nor do we derive always consistent disk inclinations for the two lines. We conclude that the evidence for and against an accretion disk origin for the Fe Kα emission is equivocal. The bulk of the data requires a very disparate set of line fits, shedding little light on a coherent physical model. We briefly consider alternatives to disk-emission and show that a simple bicone model can reproduce the Fe line profiles equally well.

X‐Ray Signatures of an Ionized Reprocessor in the Seyfert Galaxy Ton S180

We discuss the hard X-ray properties of the Seyfert galaxy Ton S180 based on the analysis of ASCA data. We find the X-ray flux varied by a factor ~2 on a timescale of a few thousand seconds. The source showed a significantly higher amplitude of variability in the 0.5-2 keV band than in the 2-10 keV band. The continuum is adequately parameterized as a Γ ~ 2.5 power law across the 0.6-10 keV band. We confirm the recent discovery of an emission line of high equivalent width due to Fe K shell emission from highly ionized material. These ASCA data show the Fe line profile to be broad and asymmetric, and they tentatively suggest it is stronger during the X-ray flares, which is consistent with an origin from the inner parts of an accretion disk. The X-ray spectrum is complex below 2 keV, possibly because of emission from a blend of soft X-ray lines, which would support the existence of an ionized reprocessor most likely due to a relatively high accretion rate in this source.

Hydrodynamical instabilities and mixing in SN 1987A - Two-dimensional simulations of the first 3 months

Results are presented from numerical simulations of the early stages of the explosion of SN 1987A. Using a two-dimensional cylindrical geometry version of a smooth particle hydrodynamics code, the explosion is followed for three months to investigate both the early hydrodynamical instabilities and the effect of the subsequent radioactive decay of Ni-56 and Co-56 with half-lives of 6.1 and 77.8 days, respectively. It is shown that the mixing induced by hydrodynamical instabilities occurring during the first few hours is substantially modified at later time by the radioactive decay of Ni-56 and Co-56. The inner cavity of the expanding supernova remnant fills up with nickel, its decay products thus forming a giant 'nickel bubble'. The peak velocity of the nickel increases by approximately 30 percent after the decays. While these results adequately model the core of the observed Fe line profiles, they fail to reproduce the high velocity wings of the spectra.