Delving into the depths of NGC 3783 with XRISM

We present a qualitative search for ultra-fast outflows (UFOs) in excess variance spectra of radio-quiet active galactic nuclei (AGNs). We analyse 42 sources from the spectroscopic UFO detection sample, and an additional 22 different sources from the variability sample. A total of 58 sources have sufficient observational data from XMM–Newton EPIC-pn and variability for an excess variance spectrum to be calculated. We examine these spectra for peaks corresponding to variable blue-shifted H- and He-like ion absorption lines from UFOs. We find good evidence for such outflows in 28 per cent of the AGN sample and weak evidence in a further 31 per cent, meaning that ∼30–60 per cent of the AGN sample hosts such UFOs. The mean and median blue-shifted velocity is found to be ∼0.14c and 0.12c, respectively. Current variability methods allow for a fast, model-independent determination of UFOs; however, further work needs to be undertaken to better characterize the statistical significance of the peaks in these spectra by more rigorous modelling. Detecting good evidence for variable UFO lines in a large number of sources also lays the groundwork for detailed analysis of the variability time-scales of the absorbers. This will allow us to probe their densities and hence distances from the central supermassive black hole.

The detection of blueshifted absorption lines likely associated with ionized iron K-shell transitions in the X-ray spectra of many active galactic nuclei (AGNs) suggests the presence of a highly ionized gas outflowing with mildly relativistic velocities (0.03c–0.6c) named ultra-fast outflow (UFO). Within the SUBWAYS project, we characterized these winds starting from a sample of 22 radio-quiet quasars at an intermediate redshift (0.1 ≤ z ≤ 0.4) and compared the results with similar studies in the literature on samples of local Seyfert galaxies (i.e., 42 radio-quiet AGNs observed with XMM-Newton at z ≤ 0.1) and high redshift radio-quiet quasars (i.e., 14 AGNs observed with XMM-Newton and Chandra at z ≥ 1.4). The scope of our work is a statistical study of UFO parameters and incidence considering the key physical properties of the sources, such as supermassive black hole (SMBH) mass, bolometric luminosity, accretion rates, and spectral energy distribution (SED) with the aim of gaining new insights into the UFO launching mechanisms. We find indications that highly luminous AGNs with a steeper X-ray/UV ratio, αox, are more likely to host UFOs. The presence of UFOs is not significantly related to any other AGN property in our sample. These findings suggest that the UFO phenomenon may be transient. Focusing on AGNs with UFOs, other important findings from this work include: (1) faster UFOs have larger ionization parameters and column densities; (2) X-ray radiation plays a more crucial role in driving highly ionized winds compared to UV; (3) the correlation between outflow velocity and luminosity is significantly flatter than what is expected for radiatively driven winds; (4) more massive black holes experience higher wind mass losses, suppressing the accretion of matter onto the black hole; (5) the UFO launching radius is positively correlated with the Eddington ratio. Furthermore, our analysis suggests the involvement of multiple launching mechanisms, including radiation pressure and magneto-hydrodynamic processes, rather than pointing to a single, universally applicable mechanism.

The fact that luminous X-ray coronae and Ultra-Fast Outflows (UFOs) are both inferred to originate from the innermost regions of active galactic nuclei (AGNs) suggests a deep physical connection between them. However, standard magnetic buoyancy models struggle to transport sufficient energy through the radiation–pressure-dominated inner disc to sustain both the phenomena, creating a theoretical energy deficit. In this work, we propose an outflow-based model with energy transport enhanced by the photon bubble instability (PBI) in the inner region. By coupling this enhanced energy supply with the MHD turbulence-driven mass-loading mechanism appropriate for weakly magnetized standard discs, we solve the dynamical and thermodynamic structure of the corona. We find that the model can successfully launch high speed winds matching observed UFO kinematics provided the mechanical acceleration efficiency is high ($f_{\rm acc}\gtrsim 0.5$). Furthermore, the model naturally reproduces the observed spectral evolution found in AGN coronae: as the accretion rate increases, the corona becomes optically thicker and cooler and produces a softer spectrum. Our results support an extended slab-like coronal geometry and suggest that UFOs and X-ray coronae in the inner discs are manifestations of the same magnetic activity.

Outflows from active galactic nuclei may be produced by absorption of continuum radiation by UV resonance lines of abundant metal ions, as observed in broad absorption line quasars (BALQs). The radiation pressure exerted on the metal ions is coupled to the rest of the gas through Coulomb collisions of the metal ions. We calculate the photon density and gas density which allow decoupling of the metal ions from the rest of the gas. These conditions may lead to an outflow composed mostly of the metal ions. We derive a method to constrain the metals/H ratio of observed UV outflows, based on the Ly {\alpha} and Si iv {\lambda}{\lambda}1394, 1403 absorption profiles. We apply this method to an SDSS sample of BALQs to derive a handful of candidate outflows with a higher than solar metal/H ratio. This mechanism can produce ultra fast UV outflows, if a shield of the continuum source with a strong absorption edge is present.

Aims. We study the origin of the anomalous deep absorption in a spectrum of the SDSS J110511.15+530806.5 distant quasar (z = 1.929) obtained by the Sloan Digital Sky Survey in Data Release 14 of the optical catalog. We aim to estimate the velocity of absorbing material, and we show that this material considerably affects our measurements of the black hole (BH) mass in massive quasars with the use of common virial mass estimators. Methods. The spectral shape of the quasar was modeled assuming that the accretion disk emission is influenced by a hot corona, warm skin, and absorbing material located close to the nucleus. The whole analysis was undertaken with XSPEC models and tools. The overall spectral shape was represented with the AGNSED model, while the deep absorption is well described by two Gaussians. Results. The observed spectrum and the fitting procedure allowed us to estimate the BH mass in the quasar as 3.52 ± 0.01 × 109 M⊙, the nonzero BH spin is a* = 0.32 ± 0.04, and the accretion rate is ṁ = 0.274 ± 0.001. The velocities of the detected absorbers lie in the range of 6330–108 135 km s−1. When we consider that absorption is caused by the C IV ion, one absorber is folding toward the nucleus with a velocity of 73 887 km s−1. We derived a BI index of about 20 300 km s−1 and a mass outflow rate up to 38.5% of the source accretion rate. Conclusions. The high absorption observed in SDSS J110511.15+530806.5 is evidence of fast winds that place the source in the group of objects on the border with UFO (ultra-fast outflows), strong broad absorption line, and fast failed radiatively accelerated dusty outflow (FRADO). This absorption affects the BH mass measurement by two orders of magnitude as compared to virial mass estimation.

We consider radio emission from a newborn black hole (BH), which is accompanied by a mini-disk with a mass of $\lesssim M_\odot$. Such a disk can be formed from an outer edge of the progenitor's envelope, especially for metal-poor massive stars and/or massive stars in close binaries. The disk accretion rate is typically super-Eddington and an ultrafast outflow with a velocity of $\sim 0.1\mbox{-}0.3\,c$ will be launched into the circumstellar medium. The outflow forms a collisionless shock, and electrons are accelerated and emit synchrotron emission in radio bands with a flux of $\sim 10^{26-30} \ \rm erg \ s^{-1} \ Hz^{-1}$ days to decades after the BH formation. The model predicts not only a fast UV/optical transient but also quasi-simultaneous inverse-Compton X-ray emission $\sim$ a few days after the BH formation, and the discovery of the radio counterpart with coordinated searches will enable us to identify this type of transients. The occurrence rate can be $0.1-10 \ \%$ of the core-collapse supernova rate, which makes them a promising target of dedicated radio observations such as the Jansky VLA Sky Survey.

Context. Outflows are observed in a variety of astrophysical sources. Remarkably, ultra-fast (v ≥ 0.1c), highly ionised outflows in the UV and X-ray bands are often seen in active galactic nuclei (AGNs). Depending on their kinetic power and mass outflow rate, Ėout and Ṁout, respectively, these outflows may play a key role in regulating the AGN–host galaxy co-evolution process through cosmic time and metal-feeding the surrounding circum-/inter-galactic medium. It is therefore crucial to provide accurate estimates of the wind properties, including Ṁout and Ėout. Aims. Here we concentrate on special relativistic effects concerning the interaction of light with matter moving at relativistic speed relatively to the source of radiation. Our aim is to assess the impact of these effects on the observed properties of the outflows and implement a correction for these effects in the existing spectral modelling routines. Methods. We define a simple procedure to incorporate relativistic effects in radiative transfer codes. Following this procedure, we run a series of simulations to explore the impact of relativistic effects for different outflow velocities and column densities. Results. The observed optical depth of the wind is usually considered a proxy for its column density NH, independently of the velocity of the outflow. However, our simulations show that the observed optical depth of an outflow with a given NH decreases rapidly as the velocity of the wind approaches relativistic values. This, in turn, implies that when estimating NH from the optical depth, it is necessary to include a velocity-dependent correction, already for moderate velocities (e.g. vout ≳ 0.05c). This correction linearly propagates to the derived quantities Ṁout and Ėout. Conclusions. We demonstrate that special relativistic effects must be considered in order to obtain correct estimates of Ṁout and Ėout for an outflow moving at a mildly relativistic speed relative to the illuminating source of radiation. As an example, we calculate the relativistically corrected values of Ṁout and Ėout for a sample of ∼30 ultra-fast outflows (UFOs) taken from the literature and find correction factors of 20 − 120% within the observed range of outflowing velocities (vout ≈ 0.1 − 0.3c). This brings the ratio between Ṁout and the disc accretion rate close or even above unity for the vast majority of the sources of the sample, highlighting the importance of the reported relativistic corrections to understand the growth of the most massive black holes. The next generation of high-sensitivity X-ray telescopes such as XRISM and Athena will provide a much more complete census of UFOs, especially in the fastest velocity regime where the relativistic corrections are increasingly important.

Ultraluminous X-ray sources (ULXs) are mainly powered by accretion in neutron stars or stellar-mass black holes. Accreting at rates exceeding the Eddington limit by factors of a few up to hundreds, radiation pressure is expected to inflate the accretion disc, and drive fast winds that have in fact been observed at significant fractions of the speed of light. Given the super-Eddington luminosity, the accretion disc will be thicker than in sub-Eddington accretors such as common active galactic nuclei and X-ray binaries, leading to a different spectral energy distribution and, possibly, a different thermal status of the wind. Here, we show the first attempt to calculate the photoionization balance of the winds driven by strong radiation pressure in thick discs with a focus on ULXs hosting black holes or non-magnetic neutron stars. We find that the winds are generally in thermally stable equilibrium, but long-term variations in the accretion rate and the inclination due to precession may have significant effects on the wind appearance and stability. Our model trends can explain the observed correlation between the spectral residuals around 1 keV and the ULX spectral state. We also find a possible correlation between the spectral hardness of the ULX, the wind velocity, and the ionization parameter in support of the general scenario.

The size distribution of asteroids and Kuiper belt objects in the solar\nsystem is difficult to reconcile with a bottom-up formation scenario due to the\nobserved scarcity of objects smaller than $\\sim$100 km in size. Instead,\nplanetesimals appear to form top-down, with large $100-1000$ km bodies forming\nfrom the rapid gravitational collapse of dense clumps of small solid particles.\nIn this paper we investigate the conditions under which solid particles can\nform dense clumps in a protoplanetary disk. We use a hydrodynamic code to model\nthe interaction between solid particles and the gas inside a shearing box\ninside the disk, considering particle sizes from sub-millimeter-sized\nchondrules to meter-sized rocks. We find that particles down to millimeter\nsizes can form dense particle clouds through the run-away convergence of radial\ndrift known as the streaming instability. We make a map of the range of\nconditions (strength of turbulence, particle mass-loading, disk mass, and\ndistance to the star) which are prone to producing dense particle clumps.\nFinally, we estimate the distribution of collision speeds between mm-sized\nparticles. We calculate the rate of sticking collisions and obtain a robust\nupper limit on the particle growth timescale of $\\sim$$10^5$ years. This means\nthat mm-sized chondrule aggregates can grow on a timescale much smaller than\nthe disk accretion timescale ($\\sim$$10^6 - 10^7$ years). Our results suggest a\npathway from the mm-sized grains found in primitive meteorites to fully formed\nasteroids. We speculate that asteroids may form from a positive feedback loop\nin which coagualation leads to particle clumping driven by the streaming\ninstability. This clumping, in turn reduces collision speeds and enhances\ncoagulation.} Future simulations should model coagulation and the streaming\ninstability together to explore this feedback loop further.\n

During the collapse of a massive star greater than 35- 40 M ⊙ , stellar core is considered to promptly collapse to a black hole. and stellar material may fall onto the hole greater than several solar masses with extremely high accretion rates (> 1 M ⊙ s -1 ). If the star has a sufficiently high angular momentum before the collapse, an accretion disk is likely to form around the black hole. Jets are suggested to be launched from the inner region of the accretion disk near the hole through magnetic and/or neutrino processes. Gamma-Ray Bursts (GRBs) are expected to be driven by the jets. This scenario of GRBs is called the collapsar model. Recently, magnetohydrodynamic (MHD) simulations were performed of the collapse of rapidly rotating, magnetized 25 M ⊙ and 40 M ⊙ stars in light of the collapsar model of GRBs (see papers listed at the end of the paper). For assumed angular velocity distributions and the uniform magnetic fields, the collapsars are shown to eject jets driven through the magnetic pressure. The simulations are however performed up to 4 s, which are shorter than durations of long GRBs ∼ 10 s. In the present work. we have performed long-tern (∼ 10 s), two-dimensional, MHD simulations of the collapse of a rapidly totaling, magnetized 40 M ⊙ star.

The idea of 'frozen-in' magnetic field lines for ideal plasmas is useful to explain diverse astrophysical phenomena, for example the shedding of excess angular momentum from protostars by twisting of field lines frozen into the interstellar medium. Frozen-in field lines, however, preclude the rapid changes in magnetic topology observed at high conductivities, as in solar flares. Microphysical plasma processes are a proposed explanation of the observed high rates, but it is an open question whether such processes can rapidly reconnect astrophysical flux structures much greater in extent than several thousand ion gyroradii. An alternative explanation is that turbulent Richardson advection brings field lines implosively together from distances far apart to separations of the order of gyroradii. Here we report an analysis of a simulation of magnetohydrodynamic turbulence at high conductivity that exhibits Richardson dispersion. This effect of advection in rough velocity fields, which appear non-differentiable in space, leads to line motions that are completely indeterministic or 'spontaneously stochastic', as predicted in analytical studies. The turbulent breakdown of standard flux freezing at scales greater than the ion gyroradius can explain fast reconnection of very large-scale flux structures, both observed (solar flares and coronal mass ejections) and predicted (the inner heliosheath, accretion disks, γ-ray bursts and so on). For laminar plasma flows with smooth velocity fields or for low turbulence intensity, stochastic flux freezing reduces to the usual frozen-in condition.

view Abstract Citations (25) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evolution of Magnetized Protoplanetary Disks Reyes-Ruiz, Mauricio ; Stepinski, Tomasz F. Abstract We investigate the global evolution of a turbulent protoplanetary disk in its viscous stage, incorporating the effects of Maxwell stress due to a large-scale magnetic field permeating disk. We assume that the viscous stress is given by an alpha model. A magnetic field is produced contemporaneously by an alpha omega dynamo mechanism and the resultant Maxwell stress assists the viscous stress in providing the means for disk evolution. The aim of this work is to compare the evolution of magnetized and nonmagnetized disks driven by turbulent viscosity of the same magnitude and thus assess the effects of a self-generated magnetic field on the structure and dynamical evolution of protoplanetary disks. Two illustrative examples corresponding to two different initial conditions are considered: a high-mass case that starts with a disk of 0.245 solar mass and angular momentum of 5.6 x 1052g sq cm/s, and a low-mass that case starts with a disk of 0.11 solar mass and angular momentum of 1.8 x 1052g sq cm/s. For each of these two cases the radial development of a disk is calculated numerically assuming a fiducial value of the dimensionless viscosity parameter alphass = 0.01, as well as alphass = 2 x 10-3. In all cases the central star has a mass equal to 1 solar mass. The most striking feature of magnetized disk evolution is the presence of the surface density bulge located in the region of the disk where the dynamo mechanism cannot support a magnetic field. The bulge persists for a time of the order of 105-106 yr. The presence and persistence of the surface density bulge may have important implications for the process of planet formation and the overall characteristics of resultant planetary systems. Publication: The Astrophysical Journal Pub Date: January 1995 DOI: 10.1086/175120 Bibcode: 1995ApJ...438..750R Keywords: Accretion Disks; Magnetic Fields; Planetary Evolution; Protoplanets; Viscosity; Finite Difference Theory; Ionization; Planetary Systems; Turbulence; Astrophysics; ACCRETION; ACCRETION DISKS; MAGNETOHYDRODYNAMICS: MHD; STARS: PLANETARY SYSTEMS full text sources ADS |

Millisecond X-ray pulsars have weak magnetic dipole moments of ∼1016 T m3 compared to ordinary X-ray pulsars with dipole moments of 1020 T m3. For this reason a surrounding accretion disc can extend closer to the millisecond X-ray pulsars, and thus reach a higher temperature, at which the opacity is dominated by electron scattering and radiation pressure is strong. We compute the self-similar structure of such a geometrically thin axisymmetric accretion disc with an internal dynamo. Such models produce significantly stronger torques on the neutron star than models without dynamos, and can explain the strong spin variations in some millisecond X-ray pulsars.

In order to study the outflows from accretion disks, we solve the set of hydrodynamic equations for accretion disks in the spherical coordinates ($r\theta\phi$) to obtain the explicit structure along the $\theta$ direction. Using self-similar assumptions in the radial direction, we change the equations to a set of ordinary differential equations (ODEs) about the $\theta$-coordinate, which are then solved with symmetrical boundary conditions in the equatorial plane, and the velocity field is obtained. The $\alpha$ viscosity prescription is applied and an advective factor $f$ is used to simplify the energy equation.The results display thinner, quasi-Keplerian disks for Shakura-Sunyaev Disks (SSDs) and thicker, sub-Keplerian disks for Advection Dominated Accretion Flows (ADAFs) and slim disks, which are consistent with previous popular analytical models. However, an inflow region and an outflow region always exist, except when the viscosity parameter $\alpha$ is too large, which supports the results of some recent numerical simulation works. Our results indicate that the outflows should be common in various accretion disks and may be stronger in slim disks, where both advection and radiation pressure are dominant. We also present the structure dependence on the input parameters and discuss their physical meanings. The caveats of this work and possible improvements in the future are discussed.

The spectral evolution of accretion disks in X-ray binaries containing black holes is studied, based on the disk instability model. The thermal transition of the outer portions of the disk controls the mass flow rate into the inner portions of the disk, thus modulating the soft X-ray flux which is thought to arise from the inner disk. Calculated soft X-ray spectra are consistent with the observations of the X-ray transient A0620 - 00 and especially ASM 2000 + 25, the soft X-ray spectra of which are well fitted by blackbody radiation with a fixed inner edge of the disk, Rin, and with monotonically decreasing temperature at Rin with time. Since the gas pressure is always dominant over the radiation pressure during the decay in these models, a two-temperature region is difficult to create. Instead, it is suggested that hard X-rays are generated in a hot (kT greater than 10 keV) accretion disk corona above the cool (kT less than 1 keV) disk.