Relativistic Line Research Articles

Accretion disks and relativistic line broadening in boson star spacetimes

Accretion disks and relativistic line broadening in boson star spacetimes

Disc wind or disc line? The extraordinary Fe-K feature of Mrk 1513

We discuss the origin of a very unusual spectral structure observed in the Fe-K band of the Seyfert galaxy Mrk 1513, a local (z = 0.063) active galactic nucleus (AGN) that is efficiently accreting matter onto its central supermassive black hole (Lbol/LEdd ∼ 0.5). We consider the highest quality X-ray observation of this source available to date, performed in 2003 by XMM–Newton. The hard X-ray spectrum is characterised by a remarkable spectral drop at ∼7 keV, which can be interpreted as either the onset of a broad absorption trough or the blue wing of a relativistic emission line. Overall, this complex feature is significant at > 5σ, and it is qualitatively reminiscent of a P Cygni profile. A serendipitous spectrum of lower quality taken by XMM–Newton in 2015 qualitatively confirms the presence of similar Fe-K structures. Although it is not possible to distinguish between the two physical scenarios on sheer statistical grounds with the current data, several considerations lend weight to the possibility that Mrk 1513 is actually hosting a persistent outflow at accretion-disc scales, thus adding to the select number of known AGN in which a wide-angle X-ray wind has been identified so far.

Moving Corona and the Line Profile of the Relativistic Broad Iron Emission Line

Iron fluorescence emission lines from X-ray binaries and active galactic nuclei are important diagnostic tools for studying the physical processes near the event horizon of both the stellar-mass black holes in X-ray binaries and the supermassive black holes in active galactic nuclei. In this work, we investigate the line profile of the relativistic broad iron lines from the cool accretion disk of a black hole due to the asymmetric illumination of a moving corona, which moves away from the disk with a relativistic velocity. Both the off-axis location and the radial velocity of the moving corona are considered. Our results clearly show that the illumination and the line profile are dependent on the position and velocity of the corona, since the disk region below the corona receives more flux, which is the most important factor affecting the line profiles. As expected, if the corona is close to the receding part of the rotating disk, the red peak is enhanced, while the blue peak is weakened in the broad line profile, and the central energy of the emission line is low. Conversely, if the corona is close to the approaching part of the disk, the blue peak is strong and the central energy of the emission line is high, even higher than the intrinsic energy of the emission line. Due to the beaming effect of the moving corona, the corona with high velocity illuminates the outer region of the disk, which leads to the red peak disappearing and there being only one blue peak in the profile of the emission line.

Large-scale structure power spectrum from scalar–tensor gravity

This work deals with the computation of the power spectrum of large-scale structure using the dynamical system approach for a multifluid universe in scalar–tensor theory of gravity. We use the 1 + 3 covariant approach to obtain evolution equations and study the behavior of the matter power spectrum of perturbation equations. The study is based on the equivalence between f(R) theory of gravity and scalar–tensor theory of gravity. We find that, for power-law [Formula: see text] models, with [Formula: see text], we have the power spectrum evolving above general relativistic scale-invariant line. For [Formula: see text], the power spectrum starts with constant amplitude then it experiences oscillations and eventually saturates at finite amplitude. Such behavior is consistent with other observations in the literature. The result supports the ongoing investigations of the equivalence between f(R) and scalar–tensor theory at linear order.

Response of the Fe Kα line emission to the X-ray continuum variability in the changing-look active galactic nucleus NGC 1566

NGC 1566 is a changing look AGN known to exhibit recurrent X-ray outbursts with each lasting for several years. The most recent X-ray outburst is observed on 2018, with a substantial increase of 2–10 keV flux by a factor of ∼24 than the historical minimum. We re-analyze the XMM-Newton and NuSTAR observations covering the pre-outburst, outburst and post-outburst epochs, and confirm the discovery of the broad feature in the ∼5–7 keV band during the period of outburst that could be interpreted as a relativistic Fe Kα emission line. Our analysis suggests that its flux has increased in tandem with the 2–10 keV continuum, making it the second changing look AGN in which the broad Fe Kα line responds to the X-ray continuum variability. This behavior strongly supports the idea that X-rays originates in a corona above the accretion disk, and disk reflection produces the relativistic Fe Kα line. In addition, we find the response of narrow Fe Kα emission line to the changes in the X-ray continuum on a time-scale as short as four months, allowing to put the location of line-emitting region at <0.1 pc, comparable to the size of optical BLR. By comparing to the changing look AGN NGC 2992, the Fe Kα variation rate (the ratio of Fe Kα variation to luminosity variation) in NGC 1566 appears greater, which could be possibly explained by larger amount of gas or Fe abundance responsible for producing the Fe Kα line for the latter. The strength of variable broad Fe Kα line as well as the soft X-ray excess emission appears to be correlated with the accretion rate, which could be explained as due to the state transition associated with the changing-look phenomenon.

Photoionization Models for High-density Gas

Abstract Relativistically broadened and redshifted 6.4–6.9 keV iron K lines are observed from many accretion powered objects, including X-ray binaries and active galactic nuclei. The existence of gas close to the central engine implies large radiation intensities and correspondingly large gas densities if the gas is to remain partially ionized. Simple estimates indicate that high gas densities are needed to allow for the survival of iron against ionization. These are high enough that rates for many atomic processes are affected by mechanisms related to interactions with nearby ions and electrons. Radiation intensities are high enough that stimulated processes can be important. Most models currently in use for interpreting relativistic lines use atomic rate coefficients designed for use at low densities and neglect stimulated processes. In our work so far we have presented atomic structure calculations with the goal of providing physically appropriate models at densities consistent with line-emitting gas near compact objects. In this paper we apply these rates to photoionization calculations, and produce ionization balance curves and X-ray emissivities and opacities that are appropriate for high densities and high radiation intensities. The final step in our program will be presented in a subsequent paper in which model atmosphere calculations will incorporate these rates into synthetic spectra.

The classical Doppler-broadened absorption line profile due to thermal effect

The classical Doppler-broadened absorption line profile, which is exactly derived by the classical Doppler effect and Maxwell speed distribution for the first time, is asymmetrically broadened with red-shift more than blue-shift, and its peak is red-shifted. Nonetheless, the half-width at half-maximum in the blue-shift wing is larger than that in the red-shift wing. The classical Doppler-broadened absorption line profile is different from the classical Doppler-broadened emission line profile. The classical Doppler-broadened absorption line profile is applied to disprove one of the two existing relativistic Doppler-broadened absorption line profiles. Also, line-shape models based on the classical Doppler-broadened absorption line profile are suggested for absorption line spectroscopy.

X-Ray Quasi-periodic Oscillations in the Lense–Thirring Precession Model. II. Variability of the Relativistic Iron Kα Line

Abstract The reprocessing of primary X-ray emission in the accretion disk of black hole X-ray binaries (BHXRBs) produces a reflection spectrum with the characteristic Fe Kα fluorescence line. Strong low-frequency quasi-periodic oscillations (QPOs) are observed from BHXRBs, and the dependence of QPO properties (e.g., phase lag) on the inclination angle suggests that the observed QPO may be associated with a geometrical effect, e.g., the precession of the X-ray source due to frame dragging near the spinning black hole. Here, in the scenario of the Lense–Thirring precession of the X-ray source, we use a Monte Carlo simulation of radiative transfer to study the irradiation/reflection and the resultant spectral properties including the Fe Kα line as a function of precession phase (time). We found that the reflection fraction, i.e., the ratio of incident flux toward the disk and the direct flux toward the observer at infinity, is modulated by the precession phase, which depends on the truncation radius (i.e., the spectral state in the truncated disk model) and the inclination angle. The Fe Kα line profile also changes as the primary X-ray source precesses, with the line luminosity and the flux-weighted centroid energy varying with the precession phase. The periodically modulated 2–10 keV continuum flux could apparently lag the line luminosity in phase, if the truncation radius is small enough for Doppler effects due to disk orbital motion to significantly affect the observed radiation.

Testing The Lamp-Post and Wind Reverberation Models with XMM-Newton Observations of NGC 5506.

The lamp-post geometry is often used to model X-ray data of accreting black holes. Despite its simple assumptions, it has proven to be powerful in inferring fundamental black hole properties such as the spin. Early results of X-ray reverberations showed support for such a simple picture, though wind-reverberation models have also been shown to explain the observed delays. Here, we analyze new and old XMM-Newton observations of the variable Seyfert-1 galaxy NGC 5506 to test these models. The source shows an emission line feature around 6.7 keV that is delayed relative to harder and softer energy bands. The spectral feature can be modeled with either a weakly relativistic disk line or by scattering in distant material. By modeling both the spectral and timing signatures, we find that the reflection fraction needed to explain the lags is larger than observed in the time-averaged spectrum, ruling out both a static lamp-post and simple wind reverberation models.

X-ray reverberation lags from the 1.5 Seyfert galaxy NGC 5273

ABSTRACT We present the results of X-ray spectral-timing analysis of a 90 ks XMM–Newton observation of the nearby, broad-line, early-type AGN NGC5273. The X-ray spectrum revealed the clear presence of a reflection component at high energies, with a clear signature of a narrow iron line at 6.4 keV, consistent with distant reflection. Applying a relativistic reflection model, we found only marginal evidence for a broader relativistic line component. However, cross-spectral analysis revealed that, between 4 and 6 × 10−4 Hz, the 5–8 keV band lagged the 2–3 keV band, implying reflection of the iron line from material close to the black hole. From the analysis of the lag-energy spectrum, we found a broad, but skewed line with a peak of ≈1000 s at 7.5 keV relative to the continuum, which we interpret as the iron line in the reverberation spectrum from an illuminated accretion disc. From the asymmetry in the shape of lag-energy spectrum, we also found that the source is consistent with having an inclination ≥45°.

Tidal disruption events as a site of an evolving relativistic spectral line

AbstractIn nuclei of galaxies, strong tidal forces can destroy stars passing within a critical distance from the central supermassive black hole (SMBH). Observational signatures of tidal disruption events (TDEs) depend on the environment around the SBMH horizon and the level of its accretion activity. Evidence for optical and ultraviolet spectral features has been reported in TDE flares; nevertheless, to test the effects of general relativity in the immediate vicinity of SMBH, the relativistically broadened and skewed X‐ray line would tell us significantly more useful information. This will require to proceed beyond inactive nuclei. To this end, we consider a system where the material from a disrupted star forms a gaseous ring that circularizes near the tidal radius around SMBH, it gradually spreads in radius by viscous processes and resides embedded within a hot corona. In our test calculation, the remnant trail is assumed to be fully circularized and embedded in a hot environment and illuminated by X‐rays from a surrounding corona or a jet base of (mild) active galactic nucleus activity. We show the expected effects on the observed profile and the centroid energy. In the future, the evolving spectral features can enhance the diagnostic capability and provide a novel way to reveal the parameters of TDEs in such sources; the distance of the remnant gas from the SMBH, the radial extent of the gaseous trail, and the spin of the SMBH could be measured.

Relativistic Fe Kα line in the composite X-ray spectra of radio-loud active galactic nuclei

ABSTRACT While a broad Fe Kα emission line is generally found in the X-ray spectra of radio quiet (RQ) active galactic nuclei (AGNs), this feature, commonly thought to be broadened by the relativistic effects near the central black hole, appears to be rare in their radio loud (RL) counterparts. In this paper, we carry out a detailed study of the ensemble property of the X-ray spectra, focusing on the Fe line, of 97 RL AGNs by applying the spectral stacking method to the spectra obtained with XMM–Newton. For comparison, the same analysis is also performed for 193 RQ AGNs. Both a narrow and a broad component of the Fe Kα line are detected at high significance in the stacked spectra of both samples. The broad lines can be well fitted with relativistically broadened line profiles. Our results suggest that, as in their RQ counterparts, a relativistic Fe line component is commonly present in RL AGNs, though it may not be detected unambiguously in individual objects with spectra of relatively low signal to noise. We try to constrain the average spin of the black holes for both the RL and RQ AGN samples by modelling their composite Fe line spectral profiles with relativistic disc line models. For the RL sample, the average spin is loosely constrained and a wide range is allowed except for very fast spins (&amp;lt;0.78, 90 per cent confidence), while for the RQ sample, it is constrained to be low or moderate (&amp;lt;0.24). We conclude that the more precise measurement of the black hole spins in RL AGNs has to await for the advent of future high-throughput X-ray telescopes.

HST unveils a compact mildly relativistic broad-line region in the candidate true type 2 NGC 3147

ABSTRACT NGC 3147 has been considered the best case of a true type 2 AGN: an unobscured AGN, based on the unabsorbed compact X-ray continuum, which lacks a broad-line region (BLR). However, the very low luminosity of NGC 3147 implies a compact BLR, which produces very broad lines, hard to detect against the dominant background host galaxy. Narrow (0.1 arcsec × 0.1 arcsec) slit HST spectroscopy allowed us to exclude most of the host galaxy light, and revealed an H α line with an extremely broad base (FWZI${\sim }27\, 000$ km s−1). The line profile shows a steep cut-off blue wing and an extended red wing, which match the signature of a mildly relativistic thin accretion disc line profile. It is indeed well fit with a nearly face on thin disc, at i ∼ 23°, with an inner radius at 77 ± 15 rg, which matches the prediction of $62^{+18}_{-14}$rg from the RBLR–L1/2 relation. This result questions the very existence of true type 2 AGN. Moreover, the detection of a thin disc, which extends below 100 rg in an L/LEdd ∼ 10−4 system, contradicts the current view of the accretion flow configuration at extremely low accretion rates.

Reverberation in a narrow relativistic line Seyfert galaxy

Seyfert galaxy NGC 5506 is an excellent target for X-rays reverberation, since its spectrum shows both narrow and broad components of the Kα Iron line, and its AGN shows strong X-rays variability. Using different XMM-Newton satellite observations, we study the spectrum in the energy band 2-10 keV.

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.

Simulations and Analysis of Gravitationally Redshifted Kerr Black Hole Accretion Discs

The Kerr black hole rotates with two parameters: mass M and angular momentum a and is characterized by the Kerr metric (Taylor and Wheeler 2000). Hence, a binary pair of a black hole and a star can create an accretion disc. A Kerr ray tracer algorithm was used to simulate accretion discs in the Seyfert-1 galaxy. The power law observed flux of relativistic emission lines, and Kerr Fourier image analysis methods were applied to the simulated discs. Simulated image characteristics were analyzed. Power laws were fitted to the simulated data of the Mrk110 accretion disc. Lastly, the simulated images were transformed into Fourier space and characteristics were discussed.

A NICER Spectrum of MAXI J1535–571: Near-maximal Black Hole Spin and Potential Disk Warping

Abstract We report on a Neutron star Interior Composition Explorer (NICER) observation of the Galactic X-ray binary and stellar-mass black hole candidate, MAXI J1535−571. The source was likely observed in an “intermediate” or “very high” state, with important contributions from both an accretion disk and hard X-ray corona. The 2.3–10 keV spectrum shows clear hallmarks of relativistic disk reflection. Fits with a suitable model strongly indicate a near-maximal spin parameter of and a disk that extends close to the innermost stable circular orbit, (1σ statistical errors). In addition to the relativistic spectrum from the innermost disk, a relatively narrow Fe K emission line is also required. The resolution of NICER reveals that the narrow line may be asymmetric, indicating a specific range of emission radii. Fits with a relativistic line model suggest an inner radius of for the putative second reflection geometry; full reflection models suggest that radii a few times larger are possible. The origin of the narrow line is uncertain, but a warp likely provides the most physically plausible explanation. We discuss our results in terms of the potential for NICER to reveal new features of the inner and intermediate accretion disk around black holes.

Can moral judgments be objectively justified?

An attempt is made to justify spontaneous moral judgements along anti- relativistic lines. The target of polemic is the work of G. Harman, specifically his thesis that the moral is just the result of implicit agreement of comunity. After criticising this standpoint by appeal to considerations of coherence and reliability, the author concludes by rehearsing the pragmatic point against relativism.

Systematic analysis of low/hard state RXTE spectra of GX 339–4 to constrain the geometry of the system

One of the popular models for the low/hard state of black hole binaries is that the standard accretion disk is truncated and the hot inner region produces, via Comptonization, hard X-ray flux. This is supported by the value of the high energy photon index, which is often found to be small, ∼ 1.7(< 2), implying that the hot medium is starved of seed photons. On the other hand, the suggestive presence of a broad relativistic Fe line during the hard state would suggest that the accretion disk is not truncated but extends all the way to the innermost stable circular orbit. In such a case, it is a puzzle why the hot medium would remain photon starved. The broad Fe line should be accompanied by a broad smeared reflection hump at ∼ 30 keV and it may be that this additional component makes the spectrum hard and the intrinsic photon index is larger, i.e. >2. This would mean that the medium is not photon deficient, reconciling the presence of a broad Fe line in the observed hard state. To test this hypothesis, we have analyzed the RXTE observations of GX 339–4 from the four outbursts during 2002–2011 and identify observations when the system was in the hard state and showed a broad Fe line. We have then attempted to fit these observationswith models,which include smeared reflection, to understandwhether the intrinsic photon index can indeed be large. We find that, while for some observations the inclusion of reflection does increase the photon index, there are hard state observations with a broad Fe line that have photon indices less than 2.

Detection of Reflection Features in the Neutron Star Low-mass X-Ray Binary Serpens X-1 with NICER

Abstract We present Neutron Star Interior Composition Explorer (NICER) observations of the neutron star (NS) low-mass X-ray binary Serpens X-1 during the early mission phase in 2017. With the high spectral sensitivity and low-energy X-ray passband of NICER, we are able to detect the Fe L line complex in addition to the signature broad, asymmetric Fe K line. We confirm the presence of these lines by comparing the NICER data to archival observations with XMM-Newton/Reflection Grating Spectrometer (RGS) and NuSTAR. Both features originate close to the innermost stable circular orbit (ISCO). When modeling the lines with the relativistic line model relline, we find that the Fe L blend requires an inner disk radius of R ISCO and Fe K is at R ISCO (errors quoted at 90%). This corresponds to a position of km and km for a canonical NS mass ( ) and dimensionless spin value of a = 0. Additionally, we employ a new version of the relxill model tailored for NSs and determine that these features arise from a dense disk and supersolar Fe abundance.