Dependence of acoustic surface gravity on disc thickness for accreting astrophysical black holes
Susovan Maity, Pratik Tarafdar, Md. Arif Shaikh, Tapas K. Das
备注：
This paper has been withdrawn by the authors, because the whole work has extensively been updated later on, hence the present version may be misleading. In addition, some errors are present in one of the calculations. We thus, would like to rewrite the whole manuscript from a different perspective and would like to submit that manuscript as a fresh one
For axially symmetric accretion maintained in hydrostatic equilibrium along the vertical direction, we investigate how the characteristic features of the embedded acoustic geometry depends on the background Kerr metric, and how such dependence is governed by three different expressions of the thickness of the matter flow. We first obtain the location of the sonic points and stationary shock between the sonic points. We then linearly perturb the flow to obtain the corresponding metric elements of the acoustic space-time. We thus construct the causal structure to establish that the sonic points and the shocks are actually the analogue black hole type and white hole type horizons, respectively. We finally compute the value of the acoustic surface gravity as a function of the spin angular momentum of the rotating black hole for three different flow thicknesses considered in the present work. We find that for some flow models, the intrinsic acoustic geometry, although in principle may be extended up to the outer gravitational horizon of the astrophysical black hole, cannot be constructed beyond a certain truncation radius as imposed by the expressions of the thickness function of the corresponding flow.
By taking into account the effect of toroidal magnetic field and its correspond heating, we determine the thickness of advection-dominated accretion flows. We consider an axisymetric, rotating, steady viscous-resistive, magnetized accretion flow under an advection dominated stage. The dominant mechanism of energy dissipation is assumed to be turbulence viscosity and magnetic diffusivity. We adopt a self-similar assumption in the radial direction to obtain the dynamical quantities, that is, radial, azimuthal, sound and Alfv\' en velocities. Our results show the vertical component of magnetic fo…
For general relativistic, inviscid, axisymmetric flow around Kerr black hole one may choose different flow thickness. The stationary flow equations can be solved using methods of dynamical system to get transonic accretion flows , i.e, flow infalling in the blackhole that turns supersonic from subsonic with decreasing radial distance, or vice versa. This transonic flows are obtained by choosing the particular flow passing through critical points of phase portrait. For certain flow thickness like the one maintaining conical shape, the sonic point coincide with the critical point. But there are …
General relativistic, axisymmetric flow of low angular momentum accretion around a Kerr black hole can have certain geometric configuration where the flow is maintained in hydrostatic equilibrium along the vertical direction (direction orthogonal to the equatorial plane of the flow). The flow thickness for such accretion models becomes a function of the local radial distance measured from the black hole horizon. There are three types of functions defined in the literature which resemble the thickness of the flow for such a configuration. We formulate the equations governing the steady state as…
We study the accretion flow from a counter-rotating torus orbiting a central Kerr black hole (BH). We characterize the flow properties at the turning point of the accreting matter flow from the orbiting torus, defined by the condition $u^ϕ= 0$ on the flow torodial velocity. The counter-rotating accretion flow and jet-like flow turning point location along BH rotational axis is given. Some properties of the counter-rotating flow thickness and counter-rotating tori energetics are studied.The maximum amount of matter swallowed by the BH from the counter-rotating tori is determined by the backgrou…
Magnetic fields are important for accretion disc structure. Magnetic fields in a disc system may be transported with the accreted matter. They can be associated with either the central body and/or jet, and be fossil or dynamo excited in situ. We consider dynamo excitation of magnetic fields in accretion discs of accreting binary systems in an attempt to clarify possible configurations of dynamo generated magnetic fields. We first model the entire disc with realistic radial extent and thickness using an alpha-quenching non-linearity. We then study the simultaneous effect of feedback from the Lo…
Accreting pulsars power relativistic jets, and display a complex spin phenomenology. These behaviours may be closely related to the large-scale configuration of the star's magnetic field, shaped by its interaction with the surrounding accretion disc. Here we present the first relativistic simulations of the interaction of a pulsar magnetosphere with an accretion flow. Our axisymmetric simulations treat the magnetospheric, or coronal, regions using a resistive extension of force-free electrodynamics. The magnetic field is also evolved inside the disc, which is a defined volume with a specified …
Accreting millisecond X-ray pulsars are known to provide a wealth of physical information during their successive states of outburst and quiescence. Based on the observed spin-up and spin-down rates of these objects it is possible, among other things, to infer the stellar magnetic field strength and test models of accretion disc flow. In this paper we consider the three accreting X-ray pulsars (XTE J1751-305, IGR J00291+5934, and SAX J1808.4-3658) with the best available timing data, and model their observed spin-up rates with the help of a collection of standard torque models that describe a …
We explore a simple spherical model of optically thin accretion on a Schwarzschild black hole, and study the properties of the image as seen by a distant observer. We show that a dark circular region in the center --- a shadow --- is always present. The outer edge of the shadow is located at the photon ring radius $b_{\rm ph} \equiv \sqrt{27}r_g$, where $r_g=GM/c^2$ is the gravitational radius of the accreting mass $M$. The location of the shadow edge is independent of the inner radius at which the accreting gas stops radiating. The size of the observed shadow is thus a signature of the spacet…
The origin and stability of a thin sheet of plasma in the magnetosphere of an accreting neutron star is investigated. First the radial extension of such a magnetospheric disc is explored. Then a mechanism for magnetospheric accretion is proposed, reconsidering the bending wave explored by Agapitou, Papaloizou & Terquem (1997), that was found to be stable in ideal MHD. We show that this warping becomes unstable and can reach high amplitudes, in a variant of Pringle's radiation-driven model for the warping of AGN accretion discs (Pringle (1996)). Finally we discuss how this mechanism might give …
Accreting black holes (BHs) produce intense radiation and powerful relativistic jets, which are affected by the BH's spin magnitude and direction. While thin disks might align with the BH spin axis via the Bardeen-Petterson effect, this does not apply to jet systems with thick disks. We used fully three-dimensional general relativistic magnetohydrodynamical simulations to study accreting BHs with various BH spin vectors and disk thicknesses with magnetic flux reaching saturation. Our simulations reveal a "magneto-spin alignment" mechanism that causes magnetized disks and jets to align with the…
In this paper, we have investigated the accreting millisecond X-ray pulsars, which are rapidly rotating neutron stars in low-mass X-ray binaries. These systems show coherent X-ray pulsations that arise when the accretion flow is magnetically channeled to the stellar surface. Here, we have developed the fundamental equations for an accretion disc around accreting millisecond X-ray pulsars in the presence of a dynamo generated magnetic fields in the inner part of the disc and we have also formulated the numerical method for the structure equations in the inner region of the disc and the highest …
The wind braking model and its applications of magnetars are discussed. The decreasing torque of magnetars during outbursts, anti-glitch, and anti-correlations between radiation and timing are understandable in the wind braking model. Recent timing observations of magnetars are also consistent with the previous modeling. A magnetism-powered wind nebula and a braking index smaller than three are the two predictions. Besides isolated magnetars, there may also be accreting magnetars in binary systems and magnetars accreting from fallback disks. Observationally, ultra-luminous X-ray pulsars may be…
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 bo…
Recent advances in general relativistic magnetohydrodynamic modeling of jets offer unprecedented insights into the inner workings of accreting black holes that power the jets in active galactic nuclei (AGN) and other accretion systems. I will present the results of recent studies that determine spin-dependence of jet power and discuss the implications for the AGN radio loud/quiet dichotomy and recent observations of high jet power in a number of AGN.
University of Warwick（华威大学）；Leibniz-Institut für Astrophysik Potsdam（波茨坦莱布尼茨天体物理研究所）；University of Rome “Tor Vergata”（罗马托维加塔大学）；ESO（欧洲南方天文台）；University of Turku（图尔库大学）；IAC（加那利天体物理研究所）；SAAO（南非天文台）；INAF-OAR（意大利国家天体物理研究所罗马天文台）；INAF-OACN（意大利国家天体物理研究所那不勒斯天文台）；Durham University（杜伦大学）
Hyper-accretion discs around black holes emit copious neutrinos and anti-neutrinos. A fraction of the emitted neutrinos convert to electron-positron plasma above the disc through the annihilation reaction $ν\barν\to e^+e^-$. This process may drive relativistic jets associated with GRB explosions. We calculate the efficiency of energy deposition by neutrinos. Our calculation is fully relativistic and based on a geodesic-tracing method. We find that the efficiency of neutrino heating is a well-defined function of (i) accretion rate and (ii) spin of the black hole. It is practically independent o…
Disc-driven migration is a key evolutionary stage of supermassive black-hole binaries hosted in gas-rich galaxies. Besides promoting the inspiral, viscous interactions tend to align the spins of the black holes with the orbital angular momentum of the disc. We present a critical and systematic investigation of this problem, also known as the Bardeen-Petterson effect. We design a new iterative scheme to solve the non-linear dynamics of warped accretion discs under the influence of both relativistic frame dragging and binary companion. We characterize the impact of the disc "critical obliquity",…
Pulse profile modelling of accreting millisecond pulsars with disc occultation and its impact on parameter inference
Nanjing University（南京大学）；Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education（南京大学现代天文与天体物理教育部重点实验室）；Anton Pannekoek Institute for Astronomy, University of Amsterdam（阿姆斯特丹大学安东·潘内克天文研究所）；Gravitation and Astroparticle Physics Amsterdam (GRAPPA), University of Amsterdam（阿姆斯特丹大学引力与天体粒子物理学阿姆斯特丹中心）；University of Helsinki（赫尔辛基大学）；University of Turku（图尔库大学）
Almost all accreting black hole and neutron star X-ray binary systems (XRBs) exhibit prominent brightness variations on a few characteristic time-scales and their harmonics. These quasi-periodic oscillations (QPOs) are thought to be associated with the precession of a warped accretion disc, but the physical mechanism that generates the precessing warp remains uncertain. Relativistic frame dragging (Lense-Thirring precession) is one promising candidate, but a misaligned magnetic field is an alternative, especially for neutron star XRBs. Here, we report the discovery of 5 accreting white dwarf s…
Transient discs around isolated accreting neutron stars
Sternberg Astronomical Institute, Lomonosov Moscow State University（列别捷夫天体物理研究所，莫斯科国立大学）；Department of Physics, Lomonosov Moscow State University（物理学系，莫斯科国立大学）；The Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University（雷蒙德和贝弗利·萨克勒物理与天文学院，特拉维夫大学）；Theoretical Astrophysics, IAAT, University of Tübingen（理论天体物理学，IAAT，蒂宾根大学）
We discuss the application of simple relativistically-blurred X-ray reflection models to the determination of the spin and the inner radius of the disc in accreting black holes. Observationally, the nature of the corona is uncertain a priori, but a robust determination of the inner disk radius can be made when the disc emissivity index is tightly constrained. When the inner disc is well illuminated, the black hole spin can also be determined. Using reflection modelling derived from ray tracing, we show that robust determination of disc truncation requires that the location of the coronal sourc…
Strongly magnetized accreting stars are often hypothesized to be in `spin equilibrium' with their surrounding accretion flows, which requires that the accretion rate changes more slowly than it takes the star to reach spin equilibrium. This is not true for most magnetically accreting stars, which have strongly variable accretion outbursts on time-scales much shorter than the time it would take to reach spin equilibrium. This paper examines how accretion outbursts affect the time a star takes to reach spin equilibrium and its final equilibrium spin period. I consider several different models fo…
We study the evolution of binary systems of Ultra-luminous X-ray sources and compute their optical emission assuming accretion onto a black hole via a non standard, advection-dominated slim disc with an outflow. We consider systems with black holes of $20M_{\odot}$ and $100M_{\odot}$, and donor masses between $8M_{\odot}$ and $25M_{\odot}$. Super-critical accretion has considerable effects on the optical emission. The irradiating flux in presence of an outflow remains considerably stronger than that produced by a standard disc. However, at very high accretion rates the contribution of X-ray ir…
We perform ideal-magnetohydrodynamic axisymmetric simulations of magnetically confined mountains on an accreting neutron star, with masses less than ~0.12 solar masses. We consider two scenarios, in which the mountain sits atop a hard surface or sinks into a soft, fluid base. We find that the ellipticity of the star, due to a mountain grown on a hard surface, approaches ~2e-4 for accreted masses greater than ~1.2e-3 solar masses, and that sinking reduces the ellipticity by between 25% and 60%. The consequences for gravitational radiation from low-mass x-ray binaries are discussed.
The excess radio background seen at $\simeq 0.1-10\,{\rm GHz}$ has stimulated much scientific debate in the past years. Recently, it was pointed out that the soft photon emission from accreting primordial black holes may be able to explain this signal. We show that the expected ultraviolet photon emission from these accreting black holes would ionize the universe completely at $z>6$ and thus wash out the 21 cm absorption signature at $z\simeq$ 20 as well as be in tension with existing cosmic microwave background anisotropy and average spectral distortion limits. We discuss possible augmentatio…
We present a grid of models of accreting brown dwarf systems with circumstellar discs. The calculations involve a self-consistent solution of both vertical hydrostatic and radiative equilibrium along with a sophisticated treatment of dust sublimation. We have simulated observations of the spectral energy distributions and several broadband photometric systems. Analysis of the disc structures and simulated observations reveal a natural dichotomy in accretion rates, with \logmdot $>-$9 and $\leq -$9 classed as extreme and typical accretors respectively. Derivation of ages and masses from our sim…
In studies of accreting black holes in binary systems, empirical relations have been proposed to quantify the coupling between accretion processes and ejection mechanisms. These processes are probed respectively by means of X-ray and radio/optical-infrared observations. The relations predict, given certain accretion conditions, the expected energy output in the form of a jet. We investigated this coupling by studying the black hole candidate Swift J1753.5-0127, via multiwavelength coordinated observations over a period of ~4 years. We present the results of our campaign showing that, all along…
A radiative mechanism is proposed for magnetic flares near luminous accreting black holes. It is based on recent first-principle simulations of magnetic reconnection, which show a hierarchical chain of fast-moving plasmoids. The reconnection occurs in a compact region (comparable to the black hole radius), and the chain experiences fast Compton cooling accompanied by electron-positron pair creation. The distribution of plasmoid speeds is shaped by radiative losses, and the self-regulated chain radiates its energy in hard X-rays. The mechanism is illustrated by Monte-Carlo simulations of the tr…
We present an optical (gri) study during quiescence of the accreting millisecond X-ray pulsar IGR J00291+5934 performed with the 10.4m Gran Telescopio Canarias (GTC) in August 2014. Despite the source being in quiescence at the time of our observations, it showed a strong optical flaring activity, more pronounced at higher frequencies (i.e. the g band). Once the flares were subtracted, we tentatively recovered a sinusoidal modulation at the system orbital period in all bands, even if a significant phase shift with respect to an irradiated star, typical of accreting millisecond X-ray pulsars is…
High resolution X-ray spectra of accreting stellar mass Black Holes reveal the presence of accretion disc winds, traced by high ionisation Fe K lines. These winds appear to have an equatorial geometry and to be observed only during disc dominated states in which the radio jet is absent. Accreting neutron star systems also show equatorial high ionisation absorbers. However, the presence of any correlation with the accretion state has not been previously tested. We have studied EXO 0748-676, a transient neutron star system, for which we can reliably determine the accretion state, in order to inv…
The high energy radiation emitted by black hole X-ray binaries originates in an accretion disk, hence the variability of the lightcurves mirrors the dynamics of the disc. We study the time evolution of the emitted flux in order to find evidences, that low dimensional non-linear equations govern the accretion flow. Here we test the capabilities of our novel method to find chaotic behaviour on the two numerical time series describing the motion of a test particle around a black hole surrounded by a thin massive disc, one being regular and the other one chaotic.
We investigate the evolution of a thin viscous disc surrounding magnetic star, including the spindown of the star by the magnetic torques it exerts on the disc. The transition from an accreting to a non-accreting state, and the change of the magnetic torque across the corotation radius are included in a generic way, the widths of the transition taken in the range suggested by numerical simulations. In addition to the standard accreting state, two more are found. An accreting state can develop into a 'dead' disc state, with inner edge well outside corotation. More often, a 'trapped' state devel…
Broad emission features of abundant chemical elements, such as Iron, are commonly seen in the X-ray spectra of accreting compact objects and their studies can provide useful information about the geometry of the accretion processes. In this work, we focus our attention on GX 3+1, a bright, persistent accreting low mass X-ray binary, classified as an atoll source. Its spectrum is well described by an accretion disc plus a stable comptonizing, optically thick corona which dominates the X-ray emission in the 0.3-20 keV energy band. In addition, four broad emission lines are found and we associate…
Observations of jets from young stellar objects reveal the asymmetric outflows from some sources. A large set of $2.5$D MHD simulations has been carried out for axisymmetric viscous/diffusive disc accretion to rotating magnetized stars for the purpose of assessing the conditions where the outflows or jets are asymmetric relative to the equatorial plane. We consider initial magnetic fields that are symmetric about the equatorial plane and consist of a radially distributed field threading the disc (disc-field) and a stellar dipole field.({\bf 1}). For pure disc-fields the symmetry or asymmetry o…
The nature of ultraluminous X-ray sources (ULXs) -- off-nuclear extra-galactic sources with luminosity, assumed isotropic, $\gtrsim 10^{39}$ erg s$^{-1}$ -- is still debated. One possibility is that ULXs are stellar black holes accreting beyond the Eddington limit. This view has been recently reinforced by the discovery of ultrafast outflows at $\sim 0.1$-$0.2c$ in the high resolution spectra of a handful of ULXs, as predicted by models of supercritical accretion discs. Under the assumption that ULXs are powered by super-Eddington accretion onto black holes, we use the properties of the observ…
An outburst of the accreting X-ray millisecond pulsar SAX J1808.4-3658 in October-November 2002 was followed by the Rossi X-ray Timing Explorer for more than a month. We demonstrate how the area covered by the hotspot at the neutron star surface is decreasing in the course of the outburst together with the reflection amplitude. These trends are in agreement with the natural scenario, where the disc inner edge is receding from the neutron star as the mass accretion rate drops. These findings are further supported by the variations of the pulse profiles, which clearly show the presence of the se…
Radiation pressure role in accreting massive black hole binaries
Università degli Studi di Milano-Bicocca（米兰比可卡大学）；INFN, Sezione di Milano-Bicocca（意大利国家核物理研究所米兰比可卡分部）；Università degli Studi di Milano（米兰大学）；DiSAT, Università degli Studi dell’Insubria（因苏布里亚大学 DiSAT）
Active galactic nuclei (AGN) are massive black holes (BHs) caught in the act of accreting gas at the centre of their host galaxies. Part of the accreting mass is converted to energy and released into the surrounding medium, in a process loosely referred to as AGN feedback. Most numerical simulations include AGN feedback as a sub-grid model, wherein energy or momentum (or both) is coupled to the nearby gas. In this work, we implement a new momentum-driven model in the hydrodynamics code GIZMO, in which accretion from large scales is mediated by a sub-grid accretion disc model, and gas particles…
