arXiv subjects

J. Ferreira

Publications and source records attributed to J. Ferreira.

At least 19 recordsLinked to original sources

arXiv2026

Spectro-polarimetric study of the black hole X-ray binary Swift J1727.8-1613 in the JED-SAD framework

Context. Swift J1727.8-1613 is an X-ray binary observed during its 2023-2024 outburst, including bright and dim hard states with similar X-ray polarimetric signatures but fluxes differing by two orders of magnitude. Aims. We aim to reproduce the spectro-polarimetric properties of these two hard states. Methods. We modelled their spectra in the JED-SAD framework and computed the X-ray polarisation properties of the best-fit configurations with the MONK general relativistic radiative transfer code. Results. Both spectra are well reproduced within the JED-SAD framework, although the dominant radiative process differs: self-Comptonised bremsstrahlung in the bright state and self-Comptonised synchrotron in the dim state. In the bright state, the simulated polarisation fraction remains below the observed value of about 4%, while the polarisation angle differs from the observations by 90 degrees because of the JED's large vertical optical depth. In contrast, the dim state's simulated polarisation fraction is about 3% and its polarisation angle is perpendicular to the disk, both broadly consistent with IXPE measurements. The dim-state results are largely insensitive to the magnetic field configuration because of Faraday depolarisation. Conclusions. The dim hard state's spectro-polarimetric properties are well reproduced, whereas those of the bright state are not. We discuss a non-thermal particle distribution and electron scattering in an accretion-disk wind as possible explanations for the observed bright-state polarisation.

astro-ph.HE↗

arXiv2026

Comparison between axisymmetric numerical magnetohydrodynamical simulations and self-similar solutions of jet-emitting disks

Turbulent accretion disks threaded by a large-scale vertical field near equipartition can drive tenuous and fast self-confined jets. Self-similar solutions of these jet-emitting disks (JEDs) have been known for a long time and provide the distributions of all physical quantities, from the turbulent disk to the asymptotic regime of ideal magnetohydrodynamic (MHD) jets. However, a thorough comparison with time-dependent numerical simulations has never been achieved, mostly because mass-loss rates found in simulations were always larger than those found analytically. This tension may have cast doubt on the analytical approach, the numerical one, or both. Our goal is to bridge the gap between these two complementary approaches and settle this long-standing issue. We performed 2.5D (axisymmetric) simulations of resistive and viscous accretion disks described by the same parameter sets as analytical JED solutions. The results demonstrate an almost perfect agreement between the numerical and analytical solutions, thereby resolving the previously observed tension. The simulations also confirm that JEDs behave as dynamical attractors: starting from different initial conditions, the system consistently converges toward the expected steady-state solution. This work demonstrates that self-similar solutions provide valuable insights into accretion-ejection physics. However, as 2.5D numerical simulations which rely on alpha-prescriptions, they strongly depend on the assumptions made for turbulent terms. In contrast, 3D simulations capture the turbulence, but become prohibitively expensive when modeling large-scale astrophysical systems. We advocate for the use of global 3D simulations to investigate turbulence and to derive physically motivated prescriptions for use in 2.5D studies.

astro-ph.HE↗

arXiv2026

A high-resolution X-ray view of the ultra-fast outflow in MAXI J1810-222

In previous work, it was reported that the Galactic black hole candidate MAXI J1810-222 exhibited a notable absorption spectral feature at around 1 keV in low-resolution X-ray spectra of CCD-like detectors. The feature was correlated with the spectral state of the source, being stronger in the soft states, as it occurs in the typical Fe K winds of X-ray binaries (XRBs). However, the results hinted towards rather extreme wind velocities of up to ~0.1 c. We therefore requested and obtained an observation with XMM-Newton to take advantage of the 10-fold higher spectral resolution (R ~200-400) provided by the RGS detector in order to resolve the lines and break the degeneracy between different models and interpretations. We applied state-of-the-art models of plasma in photoionisation equilibrium and multiphase interstellar medium. Further comparisons are performed with a re-analysis of NICER and NuSTAR data. The XMM-Newton/RGS spectrum is consistent with the presence of a mildly relativistic wind, confirming the earlier indications obtained with NICER, but places tighter constraints on the outflow properties, with the lines being intrinsically broad. The data would then favour magnetically driven winds, although thermal effects may still contribute to mass loading. NuSTAR and XMM-Newton (EPIC) show a further hotter component indicating a stratified or multiphase outflow. Fe K spectra taken with calorimetric detectors (e.g., Resolve on XRISM) will enable a high-resolution view of the complex extreme outflow in this source and shed new light on outflow processes in XRBs.

astro-ph.HE↗

arXiv2025

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT) VII: the layered molecular outflow from HL Tau and its relationship with the ringed disk

The ringed disk around HL Tau stands out as the iconic signature of planet formation, but the origin of the substructures is still debated. The HL Tau system also drives a powerful bipolar wind, and we analyze its outermost component traced by CO emission, to determine the relationship of the flow with the disk and its substructures. We use ALMA observations of the ${}^{12}$CO (2-1) line at 1.3 mm, with 0.2 km/s and ~ 0.28" resolution, conducted within the ALMA-DOT project. The channel maps and position-velocity diagrams show a rich structure of concatenated bubble- and arc-shaped features, whose size and distance from the source increase with velocity. The superposition of the features generates the apparent conical shape. The tomographic reconstruction of the morphology and kinematics of the red-shifted lobe suggests the presence of distinct nested shells having higher velocity and steeper velocity gradient for shells closer to the axis, rotating in the same sense of the disk. Such configuration can be justified by different classes of models. In this paper we compare the derived wind parameters with the predictions of magnetohydrodynamic (MHD) disk winds. Under this hypothesis, the launch radii of the three outermost shells are found to be at about the position of three adjacent dust rings in the disk at 58, 72 and 86 au. The wind may be capable of removing angular momentum from the outer disk, and we derive a magnetic lever arm of $λ\sim 4 - 5$, higher than that commonly adopted for MHD winds from these regions. Interpretations are discussed. The arrangement of the wind in nested shells with brighter emission rooted at the location of ring substructures could support the results of non-ideal MHD simulations according to which magnetic instabilities can generate the disk ring-gap system with a connected layered wind, alternatively to the action of yet undetected protoplanets.

astro-ph.GA↗

arXiv2024

Influence of the turbulent magnetic pressure on isothermal jet emitting disks

The theory of jet emitting disks (JEDs) provides a mathematical framework for a self-consistent treatment of steady-state accretion and ejection. A large-scale vertical magnetic field threads the accretion disk where magnetic turbulence occurs in a strongly magnetized plasma. A fraction of mass leaves the disk and feeds the two laminar super-Alfénic jets. In previous treatments of JEDs, the disk turbulence has been considered to provide only anomalous transport coefficients, namely magnetic diffusivities and viscosity. However, 3D numerical experiments show that turbulent magnetic pressure also sets in. We included this additional pressure term using a prescription that is consistent with the latest 3D global (and local) simulations. We then solved the complete system of self-similar magnetohydrodynamic (MHD) equations, accounting for all dynamical terms. The disk becomes puffier and less electrically conductive, causing radial and toroidal electric currents to flow at the disk surface. Field lines within the disk become straighter, with their bending and shearing occurring mainly at the surface. Accretion remains supersonic, but becomes faster at the disk surface. Large values of both turbulent pressure and magnetic diffusivities allow powerful jets to be driven, and their combined effects have a constructive influence. Nevertheless, cold outflows do not seem to be able to reproduce mass-loss rates as large as those observed in numerical simulations. Our results are a major upgrade of the JED theory, allowing a direct comparison with full 3D global numerical simulations. We argue that JEDs provide a state-of-the-art mathematical description of the disk configurations observed in numerical simulations, commonly referred to as magnetically arrested disks (MADs). However, further efforts from both theoretical and numerical perspectives are needed to firmly establish this point.

astro-ph.HE↗

arXiv2024

The interplay between disk wind and magnetospheric accretion mechanisms in the innermost environment of RU Lup

Aims: Our aim is to build upon the analysis presented in our previous work by attempting to match the observational data obtained with VLTI GRAVITY for RU Lup in 2021 with an expanded radiative transfer model of Br$γ$ emission. Specifically, we will determine if the inclusion of an additional disk wind as a Br$γ$ emitter in the inner disk will be able to reproduce the trend of increasing sizes at higher velocities, as well as the observed photocenter shifts. Methods: We make use of the MCFOST radiative transfer code to solve for Br$γ$ line formation in the innermost disk of an RU Lupl-like system. From the resulting images we compute synthetic interferometric observables. We first investigate how individual parameter variations in a pure magnetospheric accretion model and a pure parameteric disk wind model translate to changes in these derived quantities. Then we attempt to reproduce the RU Lup GRAVITY data with different parameter variants of magnetospheric accretion models, disk wind models, and combined hybrid models. Results: We demonstrate that magnetospheric accretion models and disk wind models on their own can emulate certain individual characteristics from the observational results, but individually fail to comprehensively reproduce the observational trends. Disk wind plus accretion hybrid models are in principle capable of explaining the variation in characteristic radii across the line and the corresponding flux ratios. While the model parameters of the hybrid models are mostly in good agreement with the known attributes of RU Lup, we find that our best-fitting models deviate in terms of rotational period and the size of the magnetosphere. The best-fitting hybrid model does not respect the co-rotation criterion, as the magnetospheric truncation radius is about 50% larger than the co-rotation radius.

astro-ph.SR↗

arXiv2024

Energetic Particle Tracing in Optimized Quasisymmetric Stellarator Equilibria

Recent developments in the design of magnetic confinement fusion devices have allowed the construction of exceptionally optimized stellarator configurations. The near-axis expansion in particular has proven to enable the construction of magnetic configurations with good confinement properties while taking only a fraction of the usual computation time to generate optimized magnetic equilibria. However, not much is known about the overall features of fast-particle orbits computed in such analytical, yet simplified, equilibria when compared to those originating from accurate equilibrium solutions. This work aims to assess and demonstrate the potential of the near-axis expansion to provide accurate information on particle orbits and to compute loss fractions in moderate to high aspect ratios. The configurations used here are all scaled to fusion-relevant parameters and approximate quasisymmetry in various degrees. This allows us to understand how deviations from quasisymmetry affect particle orbits and what are their effects on the estimation of the loss fraction. Guiding-center trajectories of fusion-born alpha particles are traced using gyronimo and SIMPLE codes under the NEAT framework, showing good numerical agreement. Discrepancies between near-axis and MHD fields have minor effects on passing particles but significant effects on trapped particles, especially in quasihelically symmetric magnetic fields. Effective expressions were found for estimating orbit widths and passing-trapped separatrix in quasisymmetric near-axis fields. Loss fractions agree in the prompt losses regime but diverge afterward.

physics.plasm-ph↗

arXiv2024

ALMA view of the L1448-mm protostellar system on disk scales: CH$_3$OH and H$^{13}$CN as new disk wind tracers

Protostellar disks are known to accrete, however, the exact mechanism that extracts the angular momentum and drives accretion in the low-ionization "dead" region of the disk is under debate. In recent years, magneto-hydrodynamic (MHD) disk winds have become a popular solution. Yet, observations of these winds require both high spatial resolution (${\sim}10$s au) and high sensitivity, which has resulted in only a handful of MHD disk wind candidates so far. In this work we present high angular resolution (${\sim}30$ au) ALMA observations of the emblematic L1448-mm protostellar system and find suggestive evidence for an MHD disk wind. The disk seen in dust continuum (${\sim}0.9$ mm) has a radius of ${\sim}23$ au. Rotating infall signatures in H$^{13}$CO$^+$ indicate a central mass of $0.4\pm 0.1$ M$_\odot$ and a centrifugal radius similar to the dust disk radius. Above the disk, we unveil rotation signatures in the outflow traced by H$^{13}$CN, CH$_3$OH, and SO lines and find a kinematical structure consistent with theoretical predictions for MHD disk winds. This is the first detection of an MHD disk wind candidate in H$^{13}$CN and CH$_3$OH. The wind launching region estimated from cold MHD wind theory extends out to the disk edge. The magnetic lever arm parameter would be $λ_ϕ \simeq 1.7$, in line with recent non-ideal MHD disk models. The estimated mass-loss rate is ${\sim}4$ times the protostellar accretion rate ($\dot{M}_{\rm acc} \simeq 2 \times 10^{-6} M_{\odot}/yr$) and suggests that the rotating wind could carry enough angular momentum to drive disk accretion.

astro-ph.GA↗

arXiv2023

Simultaneous mm/X-ray intraday variability in the radio-quiet AGN MCG+08-11-11

Most of the Active Galactic Nuclei (AGN) are radio-quiet (RQ) and, differently from radio-loud (RL) AGN, do not show signature of large-scale and powerful jets. The physical origin of their radio emission remains then broadly unclear. The observation of flat/inverted radio spectra at GHz frequencies seems to support however the presence of an unresolved synchrotron self-absorbed region in the close environment of the supermassive black hole. Its size could be as small as that of the X-ray corona. Since synchrotron self absorption decreases strongly with frequency, these sources need to be observed in the millimetric (mm) domain. We report here a 12h simultaneous mm-X-ray observation of the RQ AGN MCG+08-11-11 by NOEMA and NuSTAR. The mm flux shows a weak but clear increase along the pointing with a fractional variability of $2.0\pm0.1$\%. The 3-10 keV flux of NuSTAR also increases and shows a fractional variability of $7.0\pm1.5$\%. A structure function analysis shows a local maximum in the mm light curve corresponding to 2-3\% of variability on timescale of $\sim2\times10^4$ seconds (100-300 $R_g$ light crossing time). Assuming an optically thick mm emitting medium, this translates into an upper limit of its size of $\sim$1300 $R_g$. The observation of fast variability in radio-mm and X-ray wavelengths, as well as a similar variability trend, well support the mm emission to be emitted by a region close, and potentially related to, the X-ray corona like an outflow/weak jet.

astro-ph.HE↗

arXiv2023

An ultrafast outflow in the black hole candidate MAXI J1810-222?

The transient X-ray source MAXI J1810-222 was discovered in 2018 and has been active ever since. A long combined radio and X-ray monitoring campaign was performed with ATCA and Swift respectively. It has been proposed that MAXI J1810-222 is a relatively distant black hole X-ray binary, albeit showing a very peculiar outburst behaviour. Here, we report on the spectral study of this source making use of a large sample of NICER observations performed between 2019 February and 2020 September. We detected a strong spectral absorption feature at $\sim$1 keV, which we have characterised with a physical photoionisation model. Via a deep scan of the parameters space, we obtained evidence for a spectral-state dependent outflow, with mildly relativistic speeds. In particular, the soft and intermediate states point to a hot plasma outflowing at 0.05-0.15 $c$. This speeds rule-out thermal winds and, hence, they suggest that such outflows could be radiation pressure or (most likely) magnetically-driven winds. Our results are crucial to test current theoretical models of wind formation in X-ray binaries.

astro-ph.HE↗

arXiv2022

A unified accretion-ejection paradigm for black hole X-ray binaries. VI. Radiative efficiency and radio-X-ray correlation during four outbursts from GX339-4

The spectral evolution of transient X-ray binaries can be reproduced by an interplay between two flows separated at a radius $R_J$: a standard accretion disk (SAD) in the outer parts and a jet-emitting disk (JED) in the inner parts. In the previous papers of this series, we recover the spectral evolution in both X-rays and radio for four outbursts of GX339-4 by playing independently with the two parameters: $R_J$ and the accretion rate $\dot{M}_{in}$. In this paper, we compare the time evolution of $R_J$ and $\dot{M}_{in}$ for the four outbursts. We show that despite the undeniable differences between the time evolution of each outburst, a unique pattern in the $\dot{M}_{in}-R_J$ plane seems to be followed by all cycles within the JED-SAD model. We call this pattern a fingerprint, and show that even the 'failed' outburst considered follows it. We also compute the radiative efficiency in X-rays during the cycles and consider its impact on the radio--X-ray correlation. Within the JED-SAD paradigm, we find that the accretion flow is always radiatively efficient in the hard states, with between $15\%$ and $40\%$ of the accretion power being radiated away at any given time. Moreover, we show that the radiative efficiency evolves with the accretion rate because of key changes in the JED thermal structure. These changes give birth to two different regimes with different radiative efficiencies: the thick disk and the slim disk. While the existence of these two regimes is intrinsically linked to the JED-SAD model, we show direct observational evidence of the presence of two different regimes using the evolution of the X-ray power-law spectral index, a model-independent estimate. We then argue that these two regimes could be the origin of the gap in X-ray luminosity in the hard state, the wiggles and different slopes seen in the radio--X-ray correlation, and even the existence of outliers.

astro-ph.HE↗

arXiv2021

Clues on jet behavior from simultaneous radio-X-ray fits of GX339-4

Understanding the mechanisms of accretion-ejection during X-ray binaries outbursts has been a problem for several decades. It is still not clear yet what controls the spectral evolution of these objects from the hard to the soft states and then back to the hard states at the end of the outburst, tracing the well-known hysteresis cycle in the hardness-intensity diagram. Moreover, the link between the spectral states and the presence/absence of radio emission is still highly debated. In a series of papers, we developed a model composed of a truncated outer standard accretion disk (SAD, from the solution of Shakura and Sunyaev) and an inner jet emitting disk (JED). In this paradigm, the JED plays the role of the hot corona while simultaneously explaining the presence of a radio jet. Our goal is to apply for the first time direct fitting procedures of the JED-SAD model to the hard states of four outbursts of GX 339-4 observed during the 2000-2010 decade by RXTE, combined with simultaneous or quasi simultaneous ATCA observations. We built JED-SAD model tables usable in Xspec as well as a reflection model table based on the Xillver model. We apply our model to the 452 hard state observations obtained with RXTE/PCA. We were able to correctly fit the X-ray spectra and simultaneously reproduce the radio flux. We show that the functional dependency of the radio emission on the model parameters (mainly the accretion rate and the transition radius between the JED and the SAD) is similar between all the rising phases of the different outbursts of GX 339-4. But it is significantly different from the functional dependency obtained in the decaying phases. This result strongly suggests a change in the radiative and/or dynamical properties of the ejection between the beginning and the end of the outburst. We discuss possible scenarios that could explain these differences.

astro-ph.HE↗

arXiv2021

Tracking the evolution of the accretion flow in MAXI J1820+070 during its hard state with the JED-SAD model

X-ray binaries in outburst typically show two canonical X-ray spectral states, i.e. hard and soft states, in which the physical properties of the accretion flow and of the jet are known to change. Recently, the JED-SAD paradigm has been proposed for black hole X-ray binaries, aimed to address the accretion-ejection interplay in these systems. According to this model, the accretion flow is composed by an outer standard Shakura-Sunyaev disk (SAD) and an inner hot Jet Emitting Disk (JED). The JED produces both the hard X-ray emission, effectively playing the role of the hot corona, and the radio jets. In this paper, we use the JED-SAD model to describe the evolution of the accretion flow in the black hole transient MAXI J1820+070 during its hard and hard-intermediate states. Contrarily to the previous applications of this model, the Compton reflection component has been taken into account. We use eight broadband X-rays spectra, including NuSTAR, NICER and Swift data, providing a total spectral coverage of 0.8-190 keV. The data were directly fitted with the JED-SAD model. Our results suggest that the optically thick disk (i.e. the SAD) does not extend down to the ISCO in any of the considered epochs. In particular, as the system evolves towards the hard/intermediate state, we find that the inner radius decreases from $\sim$60 R$_{\rm G}$ in the first observation down to $\sim$30 R$_{\rm G}$ in the last one. This trend is accompanied by an increase of the mass-accretion rate. In all hard-intermediate state observations, two reflection components, characterized by different values of ionization, are required to adequately explain the data. These components likely originate from different regions of the SAD. We show that a flared outer disk could, in principle, explain the double reflection component.

astro-ph.HE↗

arXiv2021

Expected disk wind properties evolution along an X-ray Binary outburst

Blueshifted X-ray absorption lines (preferentially from Fe XXV and Fe XXVI present in the 6-8 keV range) indicating the presence of massive hot disk winds in Black Hole (BH) X-ray binaries (XrB) are most generally observed during the soft states. It has been recently suggested that the non-detection of such hot wind signatures in the hard states could be due to the thermal instability of the wind in the ionisation domain consistent with Fe XXV and Fe XXVI. Studying the wind thermal stability requires however a very good knowledge of the spectral shape of the ionizing Spectral Energy Distribution (SED). We discuss in this paper the expected evolution of the disk wind properties during an entire outburst by using the RXTE observations of GX 339-4 during its 2010-2011 outburst. While GX 339-4 never showed signatures of a hot wind in the X-rays, the dataset used is optimal to illustrate our purposes. We compute the corresponding stability curves of the wind using the SED obtained with the Jet-Emitting Disk model. We show that the disk wind can transit from stable to unstable states for Fe XXV and Fe XXVI ions on a day time scale. While the absence of wind absorption features in hard states could be explained by this instability, their presence in soft states seems to require changes of the wind properties (e.g. density) during the spectral transitions between hard and soft states. We propose that these changes could be partly due to the variation of heating power release at the accretion disk surface through irradiation by the central X-ray source. The evolution of the disk wind properties discussed in this paper could be confirmed through the daily monitoring of the spectral transition of a high-inclination BH XrB.

astro-ph.HE↗

arXiv2021

Magnetic outflows from turbulent accretion disks: I. Vertical structure & secular evolution

Astrophysical disks are likely embedded in an ambient vertical magnetic field. This ambient field is known to drive magneto-rotational turbulence in the disk bulk but is also responsible for the launching of magnetized outflows at the origin of astrophysical jets. The vertical structure and long-term (secular) evolution of such a system lack quantitative predictions. It is nevertheless this secular evolution that is proposed to explain time variability in many accreting systems such as X-ray binaries. We compute and analyze global 3D ideal-MHD simulations of an accretion disk threaded by a large-scale magnetic field. We evaluate the role of the turbulent terms in the equilibrium of the system. We then compute the transport of mass, angular momentum, and magnetic fields in the disk to characterize its secular evolution. We perform a parameter survey to characterize the influence of disk properties on secular transport. We find that weakly magnetized disks drive jets that carry away a small fraction of the disk angular momentum. The mass-weighted accretion speed remains subsonic although, there is always an upper turbulent atmospheric region where transonic accretion takes place. We show that a strongly magnetized version of the magneto-rotational instability drives this turbulence. The disk structure is drastically different from the conventional hydrostatic picture. The magnetic field is always dragged inwards in the disk, at a velocity that increases with the disk magnetization. Beyond a threshold on the latter, the disk undergoes a profound radial readjustment. It leads to the formation of an inner accretion-ejection region with a supersonic mass-weighted accretion speed and where the magnetic field distribution becomes steady, near equipartition with the thermal pressure. This inner structure shares many properties with the Jet Emitting Disk model described by Ferreira (1997).

astro-ph.HE↗

arXiv2020

Jets from Young Stars

Jets are ubiquitous in the Universe and, as demonstrated in this volume, are seen from a large number of astrophysical objects. For a number of reasons, in particular their proximity and the abundant range of diagnostics to determine their characteristics, jets from young stars and their associated outflows may offer us the best opportunity to discover how jets are generated in general and the nature of the link between outflows and their accretion disks. Recently it has become clear that jets may be fundamental to the star formation process in removing angular momentum from the surrounding protoplanetary disk thereby allowing accretion to proceed. Moreover, with the realisation that planetary formation begins much earlier than previously thought, jets may also help forge planets by determining initial environmental characteristics. This seems to be particularly true within the so-called terrestrial planet forming zone. Here we review observations of jets from young stars which have greatly benefitted from new facilities such as ALMA, space observatories like Spitzer, Herschel and HST, and radio facilities like LOFAR and the VLA. Interferometers such as CHARA and GRAVITY are starting to make inroads into resolving how they are launched, and we can look forward to a bright future in our understanding of this phenomenon when JWST and the SKA come on stream. In addition, we examine the various magnetohydrodynamic models for how jets from young stars are thought to be generated and how observations may help us select between these various options.

astro-ph.SR↗

arXiv2020

A unified accretion-ejection paradigm for black hole X-ray binaries. V. Low-frequency quasi-periodic oscillations

We proposed that the spectral evolution of transient X-ray binaries (XrB) is due to an interplay between two flows: a standard accretion disk (SAD) in the outer parts and a jet-emitting disk (JED) in the inner parts. We showed in previous papers that the spectral evolution in X-ray and radio during the 2010-2011 outburst of GX339-4 can be recovered. We now investigate the presence of low frequency quasi-periodic oscillations (LFQPOs) during an X-ray outburst, and address the possible correlation between the frequencies of these LFQPOs and the transition radius between the two flows, rJ. We select X-ray and radio data form 3 outbursts of GX339-4. We use the method detailed in paper IV to obtain $r_J(t)$ and $\dot{m}_{in}(t)$ for each outburst to reproduce the correlated evolution of the X-ray spectra and the radio emission for 3 different activity cycles of GX339-4. We also independently search and report the detection of 7 new LFQPOs in addition to the literature. We show that the frequency of Type C QPOs can be linked to the dynamical JED-SAD transition radius rJ, rather than the radius of optically thin-thick transition. The scaling factor q such that $ν_{QPO} \simeq ν_K (r_J) / q$ is $q \simeq 70-140$, consistent during the 4 cycles and similar to previous studies. The JED-SAD hybrid disk configuration not only provides a successful paradigm allowing us to describe XrB cycles, but also matches the QPO frequencies evolution. QPOs provide an indirect way to probe the JED-SAD transition radius, where an undetermined process produces secular variability. The demonstrated relation between the transition radius links Type C QPOs to the transition between the two flows, tying it to the inner magnetized structure of the jets. This direct connection between the jets' structure and the process responsible for Type C QPOs could naturally explain their puzzling multi-wavelength behavior.

astro-ph.HE↗

arXiv2020

Constraining MHD disk winds with ALMA. Apparent rotation signatures and application to HH212

Large millimeter interferometers are revealing a growing number of rotating outflows, which are suggested to trace magneto-centrifugal disk winds (MHD DWs). However, their impact on disk accretion is not yet well quantified. Here we identify systematic biases in retrieving the true launch zone, magnetic lever arm, and angular momentum flux of an MHD DW from apparent rotation signatures. Synthetic position-velocity cuts are constructed from self-similar MHD DWs over a broad range of parameters, and three different methods are applied for estimating the specific angular momentum. We find that the launch radius inferred using the well-known relation from Anderson et al. (2006) can markedly differ from the true outermost launch radius $r_{out}$ of the DW. The "double-peak separation" and "flow width" methods provide only a strict lower limit to $r_{out}$. This bias is independent of angular resolution and can reach a factor ten. In contrast, the "rotation curve" method gives a good estimate of $r_{out}$ when the flow is well resolved, and an upper limit otherwise. The magnetic lever arm is always underestimated. Only comparison with synthetic predictions can take into account properly all observational effects. As an application, we present a comparison with ALMA observations of HH212 at resolutions from 250 au to 16 au, which represents the most stringent observational test of MHD DW to date. This comparison confirms our predicted biases for the double-peak separation method, and the large $r_{out}\sim40~$au and small magnetic lever arm first suggested by Tabone et al. (2017). We also derive the first accurate analytical expression for the fraction of disk angular momentum extracted by an MHD disk wind of given radial extent, magnetic lever arm, and mass flux. Application to HH212 confirms that MHD DWs are serious candidates for the steady angular momentum extraction process in young disks.

astro-ph.SR↗