Holes In Active Galactic Nuclei Research Articles

Measuring black hole spins through X-ray reflection spectroscopy and the relativistic precession model: the case of XTE J1859+226

ABSTRACT The development of techniques to measure accurately black hole spins is crucial to study the physics and astrophysics of these objects. X-ray reflection spectroscopy is currently the most popular method to estimate the spins of accreting black holes; so far it has provided a spin measurement of about 40 stellar-mass black holes in X-ray binaries and 40 supermassive black holes in active galactic nuclei. The relativistic precession model (RPM) is another method to measure the spins of stellar-mass black holes: it requires the measurement of the frequencies of three simultaneous quasi-periodic oscillations and can potentially provide precise estimates of the black hole mass and spin. However, the two methods do not seem to provide consistent results when applied to the same sources, which questions the reliability and accuracy of these measurements. Recently, the RPM has been applied to infer the spin of the black hole in XTE J1859+226. The authors found a* = 0.149 ± 0.005 (68 per cent CL). There are no other spin measurements of this source. We looked for archived RXTE observations of XTE J1859+226 with blurred reflection features and found 23 spectra suitable for measuring the spin. We employed two different models with relxill and relxillD and obtained a higher spin value from all these fits. From simultaneous fitting of seven spectra of higher quality, we found $a_* = 0.986^{+0.001}_{-0.004}$ and a* = 0.987 ± 0.003 (90 per cent CL, statistical) with relxill and relxillD, respectively. Our results confirm the discrepancy between the spin measurements inferred from the two techniques.

Synchrotron Polarization Signatures of Surface Waves in Supermassive Black Hole Jets

Supermassive black holes in active galactic nuclei are known to launch relativistic jets, which are observed across the entire electromagnetic spectrum and thought to be efficient particle accelerators. Their primary radiation mechanism for radio emission is polarized synchrotron emission produced by a population of nonthermal electrons. In this Letter, we present a global general relativistic magnetohydrodynamical (GRMHD) simulation of a magnetically arrested disk (MAD). After the simulation reaches the MAD state, we show that waves are continuously launched from the vicinity of the black hole and propagate along the interface between the jet and the wind. At this interface, a steep gradient in velocity is present between the mildly relativistic wind and the highly relativistic jet. The interface is, therefore, a shear layer, and due to the shear, the waves generate roll-ups that alter the magnetic field configuration and the shear layer geometry. We then perform polarized radiation transfer calculations of our GRMHD simulation and find signatures of the waves in both total intensity and linear polarization, effectively lowering the fully resolved polarization fraction. The telltale polarization signatures of the waves could be observable by future very long baseline interferometric observations, e.g., the next-generation Event Horizon Telescope.

Solution of AGN accretion disk structure across a wide range of parameter space

Through the study of astrophysical accretion disks, considering the central role of angular momentum transport and energy conservation in determining the structure and evolution of accretion flow, we have constructed a comprehensive set of descriptions for the structure of accretion disks around supermassive black holes in active galactic nuclei (AGNs). The equation sets take into account various possible situations (gas pressure dominance, radiation pressure dominance, different heat production mechanisms, especially considering the latest research results on the turbulent heat production mechanism caused by gravity instability, etc.). By solving this system of equations, we give a general solution that covers multiple regions of a black hole's accretion disk. This will become an important tool for the community to effectively study other physical processes in the disk (such as the birth and evolution of stars, the diffusion of heavy elements, and the dynamical interactions of compact objects embedded in the disk).

Orbital configurations of spaceborne interferometers for studying photon rings of supermassive black holes

Recent advances in technology coupled with the progress of observational radio astronomy methods resulted in achieving a major milestone of astrophysics - a direct image of the shadow of a supermassive black hole, taken by the Earth-based Event Horizon Telescope (EHT). The EHT was able to achieve a resolution of ∼20μas, enabling it to resolve the shadows of the black holes in the centres of two celestial objects: the supergiant elliptical galaxy M87 and the Milky Way Galaxy. The EHT results mark the start of a new round of development of next generation Very Long Baseline Interferometers (VLBI) which will be able to operate at millimetre and sub-millimetre wavelengths. The inclusion of baselines exceeding the diameter of the Earth and observation at as short a wavelength as possible is imperative for further development of high resolution astronomical observations. This can be achieved by a spaceborne VLBI system. We consider the preliminary mission design of such a system, specifically focused on the detection and analysis of photon rings, an intrinsic feature of supermassive black holes. Optimised Earth, Sun–Earth L2 and Earth–Moon L2 orbit configurations for the space interferometer system are presented, all of which provide an order of magnitude improvement in resolution compared to the EHT. Such a space-borne interferometer would be able to conduct a comprehensive survey of supermassive black holes in active galactic nuclei and enable uniquely robust and accurate tests of strong gravity, through detection of the photon ring features.

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.

The Seoul National University AGN Monitoring Project. IV. Hα Reverberation Mapping of Six AGNs and the Hα Size–Luminosity Relation

The broad-line region (BLR) size–luminosity relation has paramount importance for estimating the mass of black holes in active galactic nuclei (AGNs). Traditionally, the size of the Hβ BLR is often estimated from the optical continuum luminosity at 5100 Å, while the size of the Hα BLR and its correlation with the luminosity is much less constrained. As a part of the Seoul National University AGN Monitoring Project, which provides 6 yr photometric and spectroscopic monitoring data, we present our measurements of the Hα lags of high-luminosity AGNs. Combined with the measurements for 42 AGNs from the literature, we derive the size–luminosity relations of the Hα BLR against the broad Hα and 5100 Å continuum luminosities. We find the slope of the relations to be 0.61 ± 0.04 and 0.59 ± 0.04, respectively, which are consistent with the Hβ size–luminosity relation. Moreover, we find a linear relation between the 5100 Å continuum luminosity and the broad Hα luminosity across 7 orders of magnitude. Using these results, we propose a new virial mass estimator based on the Hα broad emission line, finding that the previous mass estimates based on scaling relations in the literature are overestimated by up to 0.7 dex at masses lower than 107 M ⊙.

Microquasar Cyg X-3 – a unique jet-wind neutrino factory?

ABSTRACT The origin of astrophysical neutrinos is one of the most debated topics today. Perhaps the most robust evidence of neutrino counterpart comes from supermassive black holes in active galactic nuclei associated with strongly collimated outflows, or jets, that can accelerate particles to relativistic energies and produce neutrinos through hadronic interactions. Similar outflows can also be found from X-ray binaries, or ‘microquasars’, that consist of a neutron star or a stellar-mass black hole accreting matter from a non-degenerate companion star. In some cases, these systems can accelerate particles up to GeV energies implying an efficient acceleration mechanism in their jets. Neutrino production in microquasar jets can be expected with suitable conditions and a hadronic particle population. Microquasar Cyg X-3 is a unique, short orbital period X-ray binary hosting a Wolf–Rayet companion star with a strong stellar wind. The interaction of the dense stellar wind with a relativistic jet leads to particle collisions followed by high-energy gamma-ray and potentially neutrino emission. Here, using the 10-yr neutrino candidate sample of the IceCube neutrino observatory, we find that the events with the highest spatial association with Cyg X-3 occur during short-lived high-energy gamma-ray flaring periods indicating the possible astrophysical nature of these events.

Differential Interferometric Signatures of Close Binaries of Supermassive Black Holes in Active Galactic Nuclei. II. Merged Broad-line Regions

Pairs of supermassive black holes (SMBHs) at different stages are the natural results of galaxy mergers in the hierarchical framework of galaxy formation and evolution. However, identification of close binaries of SMBHs (CB-SMBHs) with sub-parsec separations in observations are still elusive. Recently, unprecedented spatial resolutions achieved by GRAVITY/GRAVITY+ on board the Very Large Telescope Interferometer through spectroastrometry (SA) provide new opportunities to resolve CB-SMBHs. Differential phase curves of CB-SMBHs with two independent broad-line regions (BLRs) are found to have distinguished characteristic structures from a single BLR. Once the CB-SMBH evolves to the stage where BLRs merge to form a circumbinary BLR, it will hopefully be resolved by the pulsar timing array in the near future as sources of nanohertz gravitational waves. In this work, we use a parameterized model for circumbinary BLRs to calculate line profiles and differential phase curves for SA observations. We show that both profiles and phase curves exhibit asymmetries caused by the Doppler boosting effect of accretion disks around individual black holes, depending on the orbital parameters of the binary and geometries of the BLR. We also generate mock SA data using the model and then recover orbital parameters by fitting the mock data. Degeneracies between parameters contribute greatly to uncertainties of parameters but can be eased through joint analysis of multiple-epoch SA observations and reverberation mappings.

Energy-dependent flavor ratios, cascade/track spectrum tension and high-energy neutrinos from magnetospheres of supermassive black holes

The IceCube neutrino observatory measures the diffuse flux of high-energy astrophysical neutrinos by means of various techniques, and there exists a mild tension between spectra obtained in different analyses. The spectrum derived from reconstruction of muon tracks is harder than that from cascades, dominated by electron and tau neutrinos. If confirmed, this tension may provide a clue to the origin of these neutrinos, which remains uncertain. Here we investigate the possibility that this tension may be caused by the change of the flavor content of astrophysical neutrinos with energy. We assume that at higher energies, the flux contains more muon neutrinos than expected in the usually assumed flavor equipartition. This may happen if the neutrinos are produced in regions of the magnetic field so strong that muons, born in pi-meson decays, cool by synchrotron radiation faster than decay. The magnetic field of ∼104 G is required for this mechanism to be relevant for the IceCube results. We note that these field values are reachable in the immediate vicinity of supermassive black holes in active galactic nuclei and present a working toy model of the population of these potential neutrino sources. While this model predicts the required flavor ratios and describes the high-energy spectrum, it needs an additional component to explain the observed neutrino flux at lower energies.

Supermassive Black Hole Winds in X-rays: SUBWAYS

We present a new X-ray spectroscopic study of 22 luminous (2 × 1045≲Lbol/erg s−1≲ 2 × 1046) active galactic nuclei (AGNs) at intermediate redshifts (0.1 ≲ z ≲ 0.4), as part of the SUpermassive Black hole Winds in the x-rAYS (SUBWAYS) sample, mostly composed of quasars and type 1 AGNs. Here, 17 targets were observed withXMM-Newtonin 2019–2020, and the remaining 5 are from previous observations. The aim of this large campaign (1.45 Ms duration) is to characterise the various manifestations of winds in the X-rays driven from supermassive black holes in AGNs. In this paper we focus on the search for and characterisation of ultra-fast outflows (UFOs), which are typically detected through blueshifted absorption troughs in the Fe K band (E > 7 keV). By following Monte Carlo procedures, we confirm the detection of absorption lines corresponding to highly ionised iron (e.g. Fe XXVHαand Fe XXVILyα) in 7 out of 22 sources at the ≳95% confidence level (for each individual line). The global combined probability of such absorption features in the sample is > 99.9%. The SUBWAYS campaign, based onXMM-Newton, extends to higher luminosities and redshifts than previous local studies on Seyferts. We find a UFO detection fraction of ∼30% of the total sample, which is in agreement with previous findings. This work independently provides further support for the existence of highly ionised matter propagating at mildly relativistic speeds (≳0.1c) in a considerable fraction of AGNs over a broad range of luminosities, which is believed to play a key role in the self-regulated AGN feeding-feedback cycle, as also supported by hydrodynamical multi-phase simulations.

Demonstration of Ultrawideband Polarimetry Using VLBI Exploration of Radio Astrometry (VERA)

We report on recent technical developments in the front- and back-ends for the four 20 m radio telescopes of the Japanese Very-Long-Baseline Interferometry (VLBI) project, VLBI Exploration of Radio Astrometry (VERA). We present a brief overview of a dual-circular polarization receiving and ultrawideband (16 Giga bit s−1) recording systems that were installed on each of the four telescopes operating at 22 and 43 GHz bands. The wider-band capability improves the sensitivity of VLBI observations for continuum emission, and the dual-polarization capability enables the study of magnetic fields in relativistic jets ejected from supermassive black holes in active galactic nuclei and in sites of star formation and around evolved stars.We present the linear polarization intensity maps of extragalactic sources at 22 and 43 GHz obtained from the most recent test observations to show the state of the art of the VERA polarimetric observations. At the end of this article, given the realization of VLBI polarimetry with VERA, we describe the future prospects for scientific aims and further technical developments.

Magnetically arrested accretion disks launching structured jets in application to GRB and AGN engines

Context. We explore the formation, energetics, and geometry of relativistic jets along with the variability of their central engine. We study both fast and slowly rotating black holes and address our simulations to active galaxy centers as well as gamma ray burst engines. Aims. The structured jets are postulated to account for emission properties of high energy sources across the mass scale, launched from stellar mass black holes in gamma ray bursts (GRBs) and from supermassive black holes in active galactic nuclei (AGNs). Their active cores contain magnetized accretion disks and the rotation of the Kerr black hole provides a mechanism for launching relativistic jets. This process works most effectively if the mode of accretion turns out to be magnetically arrested. In this mode, the modulation of jets launched from the engine is related to internal instabilities in the accretion flow that operate on smallest time and spatial scales. As these scales are related to the light-crossing time and the black hole gravitational radius, the universal model of jet-disk connection is expected to scale with the mass of the black hole. Methods. We investigated the jet-disk connection by means of 3D general relativistic magneto-hydrodynamical simulations of the magnetically arrested disk accretion in Kerr geometry. We also quantified the variability of the disk by means of a Fourier analysis. Results. We found that the system evolution is governed by the physical parameters of the engine, such as the black hole spin and disk size, as well as disk magnetization, and we applied our scenarios to typical types of sources in AGN and GRB classes. We found that the magnetically arrested disk (MAD) scenario is applicable to AGN engines and supports persistent jet emissions. It can also be applied to GRBs, as it gives the variability pattern roughly consistent with observations. However, in some cases, strong magnetic fields may lead to jet quenching, and this effect is found to be important mainly for GRB jets. We speculate that it may be related to the strength of magnetically driven winds from the GRB engines.

Magnetic Reconnection in Black Hole Magnetospheres: Lepton Loading into Jets, Superluminal Radio Blobs, and Multiwavelength Flares

Supermassive black holes in active galactic nuclei launch relativistic jets, as indicated by observed superluminal radio blobs. The energy source of these jets is widely discussed in the theoretical framework of the Blandford–Znajek process, the electromagnetic energy extraction from rotating black holes (BHs), while the formation mechanism of the radio blobs in the electromagnetically dominated jets has been a long-standing problem. Recent high-resolution magnetohydrodynamic simulations of magnetically arrested disks exhibited magnetic reconnection in a transient magnetically dominated part of the equatorial disk near the BH horizon, which led to a promising scenario of efficient MeV gamma-ray production and subsequent electron–positron pair loading into the BH magnetosphere. We develop this scenario to build a theoretical framework on energetics, timescales, and particle number density of the superluminal radio blobs and discuss observable signatures in other wave bands. We analytically show that the nonthermal electrons emit broadband photons from optical to multi-MeV bands. The electron–positron pairs produced in the magnetosphere are optically thick for synchrotron self-absorption, so that the injected energy is stored in the plasma. The stored energy is enough to power the superluminal radio blobs observed in M87. This scenario predicts rather dim radio blobs around Sgr A*, which are consistent with no clear detection by current facilities. In addition, this scenario inevitably produces strong X-ray flares in a short timescale, which will be detectable by future X-ray satellites.

Tidal Disruption on Stellar-mass Black Holes in Active Galactic Nuclei

Active galactic nuclei (AGNs) can funnel stars and stellar remnants from the vicinity of the galactic center into the inner plane of the AGN disk. Stars reaching this inner region can be tidally disrupted by the stellar-mass black holes in the disk. Such micro tidal disruption events (micro-TDEs) could be a useful probe of stellar interaction with the AGN disk. We find that micro-TDEs in AGNs occur at a rate of ∼170 Gpc−3 yr−1. Their cleanest observational probe may be the electromagnetic detection of tidal disruption in AGNs by heavy supermassive black holes (M • ≳ 108 M ⊙) that cannot tidally disrupt solar-type stars. The reconstructed rate of such events from observations, nonetheless, appears to be much lower than our estimated micro-TDE rate. We discuss two such micro-TDE candidates observed to date (ASASSN-15lh and ZTF19aailpwl).

Do radio active galactic nuclei reflect X-ray binary spectral states?

Context.Over recent years there has been mounting evidence that accreting supermassive black holes in active galactic nuclei (AGNs) and stellar mass black holes have similar observational signatures: thermal emission from the accretion disk, X-ray coronas, and relativistic jets. Further, there have been investigations into whether or not AGNs have spectral states similar to those of X-ray binaries (XRBs) and what parallels can be drawn between the two using a hardness-intensity diagram (HID).Aims.To address whether AGN jets might be related to accretion states as in XRBs, we explore whether populations of radio AGNs classified according to their (a) radio jet morphology, Fanaroff-Riley classes I and II (FR I and II), (b) excitation class, high- and low-excitation radio galaxies (HERG and LERG), and (c) radio jet linear extent, compact to giant, occupy different and distinct regions of the AGN HID (total luminosity vs. hardness).Methods.We do this by cross-correlating 15 catalogs of radio galaxies with the desired characteristics from the literature withXMM-NewtonandSwiftX-ray and ultraviolet (UV) source catalogs. We calculate the luminosity and hardness from the X-ray and UV photometry, place the sources on the AGN HID, and search for separation of populations and analogies with the XRB spectral state HID.Results.We find that (a) FR Is and IIs, (b) HERGs and LERGs, and (c) FR I-LERGs and FR II-HERGs occupy distinct areas of the HID at a statistically significant level (p-value < 0.05), and we find no clear evidence for population distinction between the different radio jet linear extents. The separation between FR I-LERG and FR II-HERG populations is the strongest in this work.Conclusions.Our results indicate that radio-loud AGNs occupy distinct areas of the HID depending on the morphology and excitation class, showing strong similarities to XRBs.

Dark fluxes from accreting black holes through several mechanisms

We discuss the possibility that accreting black hole systems can be sources for dark matter flux through several different mechanisms. We firstly discuss two types of systems‘: coronal thermal plasmas around supermassive black holes in active galactic nuclei (AGNs), and accretion disks of stellar-mass X-ray black hole binaries (BHBs). We explore how these black hole systems may produce keV light dark matter fluxes and find that the dark fluxes from those sources might be too weak to account for the current XENON1T excess. On the other hand, black holes can be good accelerators to accrete and boost heavy dark matter particles. If considering collisions or dark electromagnetism, those particles can then escape and reach the benchmark speed of 0.1c at the detector. We also extend the black hole mass region to primordial black holes (PBHs) and discuss the possibility of contributing to keV light dark flux via superradiance of PBHs.

Internal Energy, Enthalpy and Gibb's Free Energy of Spinning Black Hole in Active Galactic Nuclei

The present paper gives a model for the change in the internal energy and enthalpy (Mahto et al., 2016) and reviews it to propose a model for change in Gibb's free energy of the Reissnner-Nordstrom black hole. This also calculates their values in AGN concluding that the enthalpy and internal energy has the same values and they are just double to that of Gibb's free energy for the same mass.

Epicyclic Oscillations around Simpson–Visser Regular Black Holes and Wormholes

We study epicyclic oscillatory motion along circular geodesics of the Simpson–Visser meta-geometry describing in a unique way regular black-bounce black holes and reflection-symmetric wormholes by using a length parameter l. We give the frequencies of the orbital and epicyclic motion in a Keplerian disc with inner edge at the innermost circular geodesic located above the black hole outer horizon or on the our side of the wormhole. We use these frequencies in the epicyclic resonance version of the so-called geodesic models of high-frequency quasi-periodic oscillations (HF QPOs) observed in microquasars and around supermassive black holes in active galactic nuclei to test the ability of this meta-geometry to improve the fitting of HF QPOs observational data from the surrounding of supermassive black holes. We demonstrate that this is really possible for wormholes with sufficiently high length parameter l.

Black Hole, Observed

The author explains black holes in the context of astronomy and astrophysics. The history of black hole research and black hole discovery are covered briefly. The author explains why supermassive black holes in active galactic nuclei are the most promising candidates for imaging black holes. The principles of radio interferometers used as observation methods are covered. The Event Horizon Telescope Collaboration, its future plans, and the role of the Korean members are introduced.

Observational signatures of close binaries of supermassive black holes in active galactic nuclei

Inspired by the General Relativity for many decades, experimental physicists and astronomers have a solid dream to detect gravitational waves (GWs) from mergers of black holes, which came true until the excellent performance of the Laser Interferometer Gravitational-Wave Observatory (LIGO) at hundreds Hz. Nano-Hz GWs are expected to be radiated by close-binaries of supermassive black holes (CB-SMBHs; defined as those with separations less than ∼0.1 pc) formed during galaxy mergers and detected through the Pulsar Timing Array (PTA) technique. As of the writing, there remains no nano-Hz GWs detection. Searching for CB-SMBHs is also observationally elusive though there exist a number of possible candidates. In this review, we focus on observational signatures of CB-SMBHs from theoretic expectations, simulations and observations. These signatures appear in energy distributions of multiwavelength continuum, long term variations of continuum, jet morphology, reverberation delay maps and spectroastrometry of broad emission lines, AGN type transitions between type-1 and type-2 (changing-look), and gaseous dynamics of circumbinary disks, etc. Unlike hundred-Hz GWs from stellar mass black hole binaries, the waveform chirping of nano-Hz GWs is too slow to detect in a reasonable human timescale. We have to resort to electromagnetic observations to measure orbital parameters of CB-SMBHs to test nano-Hz GW properties. Reverberation mapping is a powerful tool for probing kinematics and geometry of ionized gas in the gravitational well of SMBHs (single or binary) and therefore provides a potential way to determine orbital parameters of CB-SMBHs. In particular, a combination of reverberation mapping with spectroastrometry (realized at the Very Large Telescope Interferometer) will further reinforce this capability. The Atacama Large Millimeter/submillimeter Array (ALMA) and the forthcoming Square Kilometre Array (SKA) are suggested to reveal dynamics of circumbinary disks through molecular emission lines.