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Many circumbinary gas giant planets have been recently discovered. The formation mechanism of circumbinary planets on wide orbits is unclear. We investigate the formation of Delorme 1 (AB)b, a |$13 \pm 5 \ \mathrm{ M_J}$| planet, orbiting its host binary at 84 au. The planet is accreting while having an estimated age of 40 Myr, which is unexpected, as this process should have ceased due to the dissipation of the protoplanetary disc. Using the smoothed particle hydrodynamics code seren , we model three formation scenarios for this planet. In Scenario I, the planet forms in situ on a wide orbit in a massive disc (by gravitational instability), in Scenario II closer to the binary in a massive disc (by gravitational instability), and in Scenario III much closer to the binary in a less massive disc (by core accretion). Planets in Scenario I stay at the observed separation and have mass accretion rates consistent with observed value, but their final mass is too high. In Scenario II, the planet reaches the observed separation through outward migration or scattering by the binary, and has mass accretion rate comparable to the observed; however, the planet mass is above the observed value. In Scenario III, the planet's final mass and mass accretion rate are comparable to the observed ones, but the planet's separation is smaller. We conclude that all models may explain some features of the observations but not all of them, raising questions about how gas is accreted on to the planet from its circumplanetary disc, and the presumed age of the system. [ABSTRACT FROM AUTHOR]

The black hole X-ray binary H1743−322 lies in a region of the Galaxy with high extinction, and therefore it has not been possible to make a dynamical mass measurement. In this paper, we make use of a recent model which uses the X-ray reflection spectrum to constrain the ratio of the black hole mass to the source distance. By folding in a reported distance measurement, we are able to estimate the mass of the black hole to be |$12\pm 2~\text{M}_\odot {}$| (⁠|$1\sigma$| credible interval). We are then able to revise a previous disc continuum fitting estimate of black hole spin |$a_*$| (previously relying on a population mass distribution) using our new mass constraint, finding |$a_*=0.47\pm 0.10$|⁠. This work is a proof of principle demonstration of the method, showing it can be used to find the mass of black holes in X-ray binaries. [ABSTRACT FROM AUTHOR]

Whether the angular momentum of protoplanetary discs is redistributed by viscosity or extracted by magnetized winds is a long-standing question. Demographic indicators, such as gas disc sizes and stellar accretion rates, have been proposed as ways of distinguishing between these two mechanisms. In this paper, we implement one-dimensional gas simulations to study the evolution of 'hybrid' protoplanetary discs simultaneously driven by viscosity and magnetized winds, with dead zones present. We explore how the variations of disc properties, including initial disc sizes, dead zone sizes, and angular momentum transport efficiency, affect stellar accretion rates, disc surface density profiles, disc sizes, disc lifetimes, and cumulative mass-loss by different processes. Our models show that the expansion of the gas disc size can be sustained when the majority of angular momentum is removed by the magnetized wind for individual protoplanetary discs. However, when we can only observe discs via demographic screenshots, the variation of disc sizes with time is possibly diminished by the disc 'personalities', by which we mean the variations of initial disc properties among different discs. Our 'hybrid' models re-assess association of the two demographic indicators with mechanisms responsible for angular momentum transport and suggest that additional diagnostics are required to assist the differentiation. [ABSTRACT FROM AUTHOR]

Magnetized disk winds and wind-driven accretion are an essential and intensively studied dispersion mechanism of protoplanetary disks (PPDs). However, the stability of these mechanisms has yet to be adequately examined. This paper employs semi-analytic linear perturbation theories under nonideal magnetohydrodynamics, focusing on disk models whose magnetic diffusivities vary by a few orders of magnitude from the disk midplane to its surface. Linear modes are distinguished by their symmetry with respect to the midplane. These modes have qualitatively different growth rates: symmetric modes almost always decay, while at least one antisymmetric mode always has a positive growth rate. This growth rate decreases faster than the Keplerian angular velocity with cylindrical radius R in the disk and scales steeper than R −5/2 in the fiducial disk model. The growth of antisymmetric modes breaks the reflection symmetry across the disk equatorial plane, and may occur even in the absence of the Hall effect. In the disk regions where fully developed antisymmetric modes occur, accretion flows appear only on one side of the disk, while disk winds occur only on the other. This may explain the asymmetry of some observed PPD outflows. [ABSTRACT FROM AUTHOR]

Models of the resolved Event Horizon Telescope (EHT) sources Sgr A* and M87* are constrained by observations at multiple wavelengths, resolutions, polarizations, and time cadences. In this paper, we compare unresolved circular polarization (CP) measurements to a library of models, where each model is characterized by a distribution of CP over time. In the library, we vary the spin of the black hole, the magnetic field strength at the horizon (i.e., both SANE and magnetically arrested disk or MAD models), the observer inclination, a parameter for the maximum ion–electron temperature ratio assuming a thermal plasma, and the direction of the magnetic field dipole moment. We find that Atacama Large Millimeter/submillimeter Array (ALMA) observations of Sgr A* are inconsistent with all edge-on (i = 90°) models. Restricting attention to the MAD models favored by earlier EHT studies of Sgr A*, we find that only models with magnetic dipole moment pointing away from the observer are consistent with ALMA data. We also note that in 26 of the 27 passing MAD models, the accretion flow rotates clockwise on the sky. We provide a table of the means and standard deviations of the CP distributions for all model parameters, along with their trends. [ABSTRACT FROM AUTHOR]

On 2019 November 2, the black hole X-ray binary MAXI J0637−430 went into outburst, at the start of which it was observed in a thermal 'disc-dominated' state. High photon energy (extending above 10 keV) observations taken by the NuSTAR telescope reveal that this thermal spectrum cannot be fit by conventional two-component (disc plus corona) approaches that ignore disc emission sourced from within the plunging region of the black hole's space–time. Instead, these models require a third 'additional' thermal component to reproduce the data. Using new disc solutions that extend classical models into the plunging region, we show that this 'additional' thermal emission can be explained self-consistently with photons emitted from the accretion flow at radii within the innermost stable circular orbit of the black hole. This represents the second low-mass X-ray binary, after MAXI J1820+070, with a detection of plunging region emission, suggesting that signatures of this highly relativistic region may well be widespread but not previously widely appreciated. To allow for a detection of the plunging region, the black hole in MAXI J0637−430 must be at most moderately spinning, and we constrain the spin to be |$a_\bullet \lt 0.86$| at 99.9 |${{\ \rm per\ cent}}$| confidence. We finish by discussing the observational requirements for the robust detection of this region. [ABSTRACT FROM AUTHOR]

An increasing number of exoplanets have been discovered in the Milky Way galaxy, which is also known to harbour a super-massive black hole (Sagittarius A*) at its centre. Here, we investigate how the central black hole (BH) activity may affect the evolution of exoplanets in our Galaxy. Accreting BHs emit high-energy radiation – extreme ultraviolet and X-rays – which can lead to XUV photoevaporation of the planetary atmospheres. We evaluate the atmospheric mass-loss using both theoretical estimates of the BH radiative output and observational constraints on the past activity history of Sgr A*. The resulting mass-loss is analysed as a function of the galactocentric distance. For the first time, we compute the exoplanet atmospheric evolution under BH irradiation by explicitly including the temporal evolution of the central luminosity output (i.e. the BH activity history). We obtain that Sgr A* could have a major impact on exoplanets located in the inner region of the Galaxy (e.g. Galactic bulge); a significant fraction of the atmospheric mass can be removed by BH irradiation; and in extreme cases, the initial atmosphere may be completely stripped away. Such mass-loss can have important consequences on the atmospheric chemistry and potential biological evolution. We discuss the physical implications for planetary habitability, and we also briefly consider the case of stellar-mass BHs. Overall, accreting black holes may play a significant role in the evolution of exoplanets in our Galaxy across cosmic time. [ABSTRACT FROM AUTHOR]

Polarization measurements by the Event Horizon Telescope from M87* and Sgr A* suggest that there is a dynamically strong, ordered magnetic field, typical of what is expected of a magnetically arrested accretion disc (MAD). In such discs, the strong poloidal magnetic field can suppress the accretion flow and cause episodic flux eruptions. Recent work shows that general relativistic magnetohydrodynamic (GRMHD) MAD simulations feature dynamics of turbulence and mixing instabilities that are becoming resolved at higher resolutions. We perform a convergence study of MAD states exceeding the status quo by an order of magnitude in resolution. We use existing 3D simulations performed with the H-AMR code, up to a resolution of 5376 × 2304 × 2304 in a logarithmic spherical-polar grid. We find consistent time-averaged disc properties across all resolutions. However, higher resolutions reveal signs of inward angular momentum transport attributed to turbulent convection, particularly evident when mixing instabilities occur at the surfaces of flux tubes during flux eruptions. Additionally, we see wave-like features in the jet sheath, which become more prominent at higher resolutions, that may induce mixing between the jet and disc. At higher resolutions, we observe the sheath to be thinner, resulting in increased temperature, reduced magnetization, and greater variability. Those differences could affect the dissipation of energy, which would eventually result in distinct observable radiative emission from high-resolution simulations. With higher resolutions, we can delve into crucial questions about horizon-scale physics and its impact on the dynamics and emission properties of larger-scale jets. [ABSTRACT FROM AUTHOR]

The Rapid Burster is a unique neutron star low-mass X-ray binary system, showing both thermonuclear v-I and accretion-driven Type-II X-ray bursts. Recent studies have demonstrated how coordinated observations of X-ray and radio variability can constrain jet properties of accreting neutron stars – particularly when the X-ray variability is dominated by discrete changes. We present a simultaneous very large array, Swift , and INTErnational Gamma-Ray Astrophysics Laboratory observing campaign of the Rapid Burster to investigate whether its jet responds to Type-II bursts. We observe the radio counterpart of the X-ray binary at its faintest-detected radio luminosity, while the X-ray observations reveal prolific, fast X-ray bursting. A time-resolved analysis reveals that the radio counterpart varies significantly between observing scans, displaying a fractional variability of |$38 \pm 5$|  per cent. The radio faintness of the system prevents the robust identification of a causal relation between individual Type-II bursts and the evolution of the radio jet. However, based on a comparison of its low-radio luminosity with archival Rapid Burster observations and other accreting neutron stars, and on a qualitative assessment of the X-ray and radio light curves, we explore the presence of a tentative connection between bursts and jet: i.e. the Type-II bursts may weaken or strengthen the jet. The former of those two scenarios would fit with magnetorotational jet models; we discuss three lines of future research to establish this potential relation between Type-II bursts and jets more confidently. [ABSTRACT FROM AUTHOR]

4U 1954 |$+$| 31 is a high-mass X-ray binary (HMXB) that contains a neutron star (NS) and an M supergiant companion. The NS has a spin period of |$\sim 5.4$| h. The traditional wind-accreting model requires an ultra-strong magnetic field for the NS to explain its extremely long spin period, which seems problematic for the NS with age of a few |$10^7$| yr. In this work, we take into account the unsteady feature of wind accretion, which results in alternation of the direction of the wind matter's angular momentum. Accordingly, the torque exerted by the accreted wind matter varies between positive and negative from time to time, and largely cancels out over long time. In such a scenario, NSs can naturally attain long spin periods without the requirement of a very strong magnetic field. This may also provide a reasonable explanation for the spin period distribution of long-period NSs in HMXBs. [ABSTRACT FROM AUTHOR]

Disc warping, and possibly disc breaking, has been observed in protoplanetary discs around both single and multiple stars. Large warps can break the disc, producing multiple observational signatures. In this work, we use comparisons of disc time-scales to derive updated formulae for disc breaking, with better predictions as to when and where a disc is expected to break and how many breaks could occur. Disc breaking is more likely for discs with small inner cavities, cooler temperatures, and steeper power-law profiles, such that thin, polar-aligning discs are more likely to break. We test our analytical formulae using three-dimensional grid-based simulations of protoplanetary discs warped by the gravitational torque of an inner binary. We reproduce the expected warp behaviours in different viscosity regimes and observe disc breaking at locations in agreement with our derived equations. As our simulations only show disc breaking when disc viscosity is low, we also consider a viscous criterion for disc breaking, where rapid alignment to the precession vector can prevent a break by reducing the maximum misalignment between neighbouring rings. We apply these results to the GW Orionis circumtriple disc and find that the precession induced from the central stars can break the disc if it is relatively thin. We expect repeated or multiple disc breaking to occur for discs with sufficiently steep power-law profiles. We simulate a polar-aligning disc around an eccentric binary with steep power-law profiles and observe two separate breaking events at locations in rough agreement with our analytical predictions. [ABSTRACT FROM AUTHOR]

The littoral zone of the western part of Algeria is an area which has experienced significant modification in the last two decades. This paper highlights the hydro-sedimentary processes and historical shoreline evolution on the west coast of Oran. To this effect, the present work is divided into three parts: (1) a wave climate study has been established over a period of 30 years, based on Infoplaza data. (2) an assessment of sediment transport using wave data. The first method consists of estimating the longshore sediment transport rate (LSTR) from local parameters using three empirical formulas: CERC (CERC (1984) Shore protection manual (Vol. 1). Department of the Army, Waterways Experiment Station, Corps of Engineers, Coastal Engineering Research Center, p 337), Kamphuis (Kamphuis JW (2013) Uncertainty, research, science and engineering in coastal dynamics. In: The 7th International Conference on Coastal Dynamics, Arcachon, pp 927–936) and Van Rijn (Rijn, Coast Eng 90:23–39, 2014)), the results show that (LSTR) values were 8.7 × 105, 9.8 × 105 and 49 × 105 m3/year. Second, a numerical simulation was carried out by the coupled model Mike 21/3 according to the sea conditions at the local scale. (3) a diachronic shoreline evolution from 1980 to 2021 based on aerial photographs and satellite images using the Digital Shoreline Analysis System (DSAS). Based on 1191 transects, the rate of shoreline change analyzed between 1980 and 2021 indicates that the study area was slightly eroding (51%) with a rate varies between − 0.91 and + 4.02 m/year. The results of the wave simulation indicated that, waves coming from the northeast have an average wave height varies from 0.78 to 2.4 m, driven a longshore current of 0.3–0.7 m/s. The highest erosion rates were recorded in the bay of Ain El Turk and Bousfer and the highest accretion rate was measured in the Andalouses coast. [ABSTRACT FROM AUTHOR]

With the aim to study the spectral properties of some X-ray sources from recently observed Chandra data, 9 galaxies which have been observed by Chandra ACIS-S during the year 2018 to 2022 have been considered for the present work. 27 sources with net source counts ≥ 100 have been considered. The spectra of all the sources were fitted using two empirical models-an absorbed powerlaw and an absorbed disk blackbody. Based on their estimated bolometric luminosities, the 27 X-ray sources have been classified into 6 X-ray binaries (XRBs) and 21 Ultraluminous X-ray sources (ULXs). All the six XRBs are found to be in the spectrally hard state ( Γ ∼ 1.52 - 2.29 ) which indeed may be due to thermal comptonization. Only one ULX-CXOUJ032251.2-370950 (X-5) was found to be spectrally soft while the remaining 20 ULXs were spectrally hard. The spectral parameters of X-5 with an inner disk temperature (kT in ) ∼ 0.5 keV and an estimated bolometric luminosity, L X ∼ 3.26 × 10 39 erg s - 1 requires a black hole of mass, M BH ∼ 137. 86 - 47.41 + 66.62 M ⊙ accreting at ∼ 0.19 times its Eddington limit. 8 ULXs-X-4, X-8, X-9, X-10, X-11, X-12, X-20 and X-21 were found to be in the Extremely luminous X-ray sources (ELXs) regime with even their lower limit of luminosity > 10 40 erg s - 1 . Softening/Hardening of spectra with or without changes in the luminosity were also observed in some ULXs/ELXs. In the hard ELX, X-8, spectral softening with almost consistent luminosity was observed. While in the ULXs-X-20 and X-25 spectral softening with increasing luminosity was observed. However, spectral hardening with increase in luminosity were observed in the ULXs-X-21 and X-26. [ABSTRACT FROM AUTHOR]

Radiation-driven outflows play a crucial role in extracting mass and angular momentum from binary systems undergoing rapid mass transfer at super-Eddington rates. To study the mass transfer process from a massive donor star to a stellar-mass black hole (BH), we perform multidimensional radiation-hydrodynamical simulations that follow accretion flows from the first Lagrange point down to about a hundred times the Schwarzschild radius of the accreting BH. Our simulations reveal that rapid mass transfer occurring at over a thousand times the Eddington rate leads to significant mass-loss from the accretion disc via radiation-driven outflows. Consequently, the inflow rates at the innermost radius are regulated by two orders of magnitude smaller than the transfer rates. We find that convective motions within the accretion disc drive outward energy and momentum transport, enhancing the radiation pressure in the outskirts of the disc and ultimately generating large-scale outflows with sufficient energy to leave the binary. Furthermore, we observe strong anisotropy in the outflows, which occur preferentially toward both the closest and furthest points from the donor star. However, when averaged over all directions, the specific angular momentum of the outflows is nearly comparable to the value predicted in the isotropic emission case. Based on our simulation results, we propose a formula that quantifies the mass growth rates on BHs and the mass-loss rates from binaries due to radiation-driven outflows. This formula provides important implications for the binary evolution and the formation of merging binary BHs. [ABSTRACT FROM AUTHOR]

A tight correlation between the radio and X-ray emission in the hard state of black hole X-ray binaries (BHXRBs) indicates an intrinsic disc–jet connection in stellar black hole (BH) accretion systems, though the detailed physics processes at work are still quite unclear. A hot accretion flow is suggested to match the outer cold thin disc at a certain radius in the hard state, which may vary with the accretion rate. In this work, we assume that the magnetic field generated in the outer thin disc is advected inwards by the inner hot accretion flow, which is substantially enhanced near the BH. Such a strong field threading the horizon of a spinning BH is responsible for launching relativistic jets in BHXRBs via the Blandford–Znajek mechanism. Thus, both the jet power and the X-ray emission increase with the mass accretion rate, and we find that our model calculations are able to reproduce the observed radio/X-ray correlation quantitatively. For some individual BHXRBs, the slopes of the radio/X-ray correlations become steeper when the sources are brighter. Our model calculations show that this feature is due to the transition of the outer disc from gas pressure dominated to radiation pressure dominated, which leads to different accretion rate dependence of the field strength in the outer disc. [ABSTRACT FROM AUTHOR]

We assess the possibility of detecting both eccentricity and gas effects (migration and accretion) in the gravitational wave (GW) signal from LISA massive black hole binaries at redshift |$z=1$|⁠. Gas induces a phase correction to the GW signal with an effective amplitude (⁠|$C_{\rm g}$|⁠) and a semimajor axis dependence (assumed to follow a power-law with slope |$n_{\rm g}$|⁠). We use a complete model of the LISA response and employ a gas-corrected post-Newtonian inspiral-only waveform model TaylorF2Ecc. By using the Fisher formalism and Bayesian inference, we constrain |$C_{\rm g}$| together with the initial eccentricity |$e_0$|⁠ , the total redshifted mass |$M_z$|⁠ , the primary-to-secondary mass ratio q , the dimensionless spins |$\chi _{1,2}$| of both component BHs, and the time of coalescence |$t_c$|⁠. We find that simultaneously constraining |$C_{\rm g}$| and |$e_0$| leads to worse constraints on both parameters with respect to when considered individually. For a standard thin viscous accretion disc around |$M_z=10^5~{\rm M}_{\odot }$|⁠ , |$q=8$|⁠ , |$\chi _{1,2}=0.9$|⁠ , and |$t_c=4$| years MBHB, we can confidently measure (with a relative error of |$\lt 50$|  per cent) an Eddington ratio |${\rm f}_{\rm Edd}\sim 0.1$| for a circular binary and |${\rm f}_{\rm Edd}\sim 1$| for an eccentric system assuming |$\mathcal {O}(10)$| stronger gas torque near-merger than at the currently explored much-wider binary separations. The minimum measurable eccentricity is |$e_0\gtrsim 10^{-2.75}$| in vacuum and |$e_0\gtrsim 10^{-2}$| in gas. A weak environmental perturbation (⁠|${\rm f}_{\rm Edd}\lesssim 1$|⁠) to a circular binary can be mimicked by an orbital eccentricity during inspiral, implying that an electromagnetic counterpart would be required to confirm the presence of an accretion disc. [ABSTRACT FROM AUTHOR]

We present a comprehensive spectrotemporal analyses of recurrent outbursting black hole sources GX 339 |$-$| 4 and H 1743 |$-$| 322 using available AstroSat and NuSTAR archival observations during 2016–2024. The nature of the outburst profiles of both sources are examined using long-term MAXI/GSC and Swift/BAT light curves, and failed as well as successful outbursts are classified. Wide-band (0.5–60 keV) spectral modelling with disc (diskbb) and Comptonized (Nthcomp) components indicates that GX 339 |$-$| 4 transits from hard (⁠|$kT_{\rm bb}=0.12-0.77$| keV, |$\Gamma _{\rm nth}=1.54-1.74$|⁠ , and |$L_{\rm bol}=0.91-11.56$| per cent |$L_{\rm Edd}$|⁠) to soft state (⁠|$kT_{\rm in}~[\approx {kT}_{\rm bb}]=0.82-0.88$| keV, |$\Gamma _{\rm nth}=1.46-3.26$|⁠ , |$L_{\rm {bol}}=19.59-30.06~{{\ \rm per\ cent}}L_{\rm Edd}$|⁠) via intermediate state (⁠|$kT_{\rm in}~[\approx {kT}_{\rm {bb}}]=0.56-0.88$| keV, |$\Gamma _{\rm nth}=1.76-2.66$|⁠ , |$L_{\rm {bol}}=2.90-16.09~{{\ \rm per\ cent}}L_{\rm Edd}$|⁠), whereas H 1743 |$-$| 322 transits from quiescent to hard state (⁠|$\Gamma _{\rm nth}=1.57-1.71$|⁠ , |$L_{\rm {bol}}=2.08-3.48~{{\ \rm per\ cent}}L_{\rm Edd}$|⁠). We observe type-B and type-C quasi-periodic oscillations (QPOs) in GX 339 |$-$| 4 with increasing frequencies (⁠|$0.10 - 5.37$| Hz) along with harmonics. For H 1743 |$-$| 322, prominent type-C QPOs are observed in frequency range 0.22–1.01 Hz along with distinct harmonics. Energy-dependent power spectral studies reveal that fundamental QPO and harmonics disappear beyond 20 keV in GX 339 |$-$| 4, whereas fundamental QPO in H 1743 |$-$| 322 persists up to 40 keV. We also observe that type-C |${\rm QPO}_{\rm rms}\,\rm per\,cent$| decreases with energy for both sources although such variations appear marginal for type-B QPOs. Additionally, we report non-monotonic behaviour of photon index with plasma temperature and detection of annihilation line. Finally, we discuss the relevance of the observational findings in the context of accretion dynamics around black hole binaries. [ABSTRACT FROM AUTHOR]

X-ray observations of neutron star (NS) low-mass X-ray binaries (LMXBs) are useful for probing the physical processes close to the NS and for constraining source parameters. Aql X-1 is a transient NS LMXB that frequently undergoes outbursts and provides an excellent opportunity to study source properties and accretion mechanisms in a strong-gravity regime over a wide range of accretion rates. In this work, we systematically investigate the spectral evolution of Aql X-1 using NICER observations during the source outbursts in 2019 and 2020. The NICER observations cover the complete transition of the source from its canonical hard state to a soft state and back. The spectra extracted from most observations can be explained by a partially Comptonized accretion disc. We find that the system can be described by an accretion disc with an inner temperature of |$\sim 0.7$| keV and a Comptonizing medium of thermal electrons at |$\sim 2$| keV, while the photon index is strongly degenerate with the covering fraction of the medium. We also find evidence of Fe K |$\alpha$| fluorescence emission in the spectra, indicating reprocessing of the Comptonized photons. We observe an absorption column density higher than the Galactic column density for most of the observations, indicating a significant local absorption. For some of the observations in the 2020 outburst, however, the local absorption is negligible. [ABSTRACT FROM AUTHOR]

We present a new approach for stably evolving general relativistic magnetohydrodynamic (GRMHD) simulations in regions where the magnetization |$\sigma =b^2/\rho c^2$| becomes large. GRMHD codes typically struggle to evolve plasma above |$\sigma \approx 100$| in simulations of black hole accretion. To ensure stability, GRMHD codes will inject mass density artificially to the simulation as necessary to keep the magnetization below a ceiling value |$\sigma _{\rm max}$|⁠. We propose an alternative approach where the simulation transitions to solving the equations of general relativistic force-free electrodynamics (GRFFE) above a magnetization |$\sigma _{\rm trans}$|⁠. We augment the GRFFE equations in the highly magnetized region with approximate equations to evolve the decoupled field-parallel velocity and plasma energy density. Our hybrid scheme is explicit and easily added to the framework of standard-volume GRMHD codes. We present a variety of tests of our method, implemented in the GRMHD code koral , and we show results from a 3D hybrid GRMHD + GRFFE simulation of a magnetically arrested disc (MAD) around a spinning black hole. Our hybrid MAD simulation closely matches the average properties of a standard GRMHD MAD simulation with the same initial conditions in low magnetization regions, but it achieves a magnetization |$\sigma \approx 10^6$| in the evacuated jet funnel. We present simulated horizon-scale images of both simulations at 230 GHz with the black hole mass and accretion rate matched to M87*. Images from the hybrid simulation are less affected by the choice of magnetization cut-off |$\sigma _{\rm cut}$| imposed in radiative transfer than images from the standard GRMHD simulation. [ABSTRACT FROM AUTHOR]

XB 1254−690 is a neutron star low-mass X-ray binary with an orbital period of 3.88 h, and it exhibits energy-dependent intensity dips, thermonuclear bursts, and flares. We present the results of an analysis of a long observation of this source using the AstroSat satellite. The X-ray light curve gradually changed from a high-intensity flaring state to a low-intensity one with a few dips. The hardness–intensity diagram showed that the source is in a high-intensity banana state with a gradually changing flux. Based on this, we divide the observation into four flux levels for a flux-resolved spectral study. The X-ray spectra can be explained by a model consisting of absorption, thermal emission from the disc, and non-thermal emission from the corona. From our studies, we detect a correlation between the temperature of the thermal component and the flux and we examine the implications of our results for the accretion disc geometry of this source. [ABSTRACT FROM AUTHOR]

We analyse, using new analytical models and numerical general relativistic magnetohydrodynamic simulations, the three-dimensional properties of accretion flows inside the plunging region of black hole spacetimes (i.e. at radii smaller than the innermost stable circular orbit). These simulations are of thick discs, with aspect ratios of order unity |$h/r \sim 1$|⁠ , and with a magnetic field geometry given by the standard low-magnetization 'SANE' configuration. This work represents the first step in a wider analysis of this highly relativistic region. We show that analytical expressions derived in the 'thin disc' limit describe the numerical results remarkably well, despite the large aspect ratio of the flow. We further demonstrate that accretion within this region is typically mediated via spiral arms, and that the geometric properties of these spiral structures can be understood with a simple analytical model. These results highlight how accretion within the plunging region is fundamentally two-dimensional in character, which may have a number of observational implications. We derive a modified theoretical description of the pressure within the plunging region which accounts for turbulent heating and may be of use to black hole image modelling. [ABSTRACT FROM AUTHOR]

One of the ports most affected by the phenomenon of silting in Algeria is the port of Cap Djinet. In order to consider the monitoring of this port over a period of 8 years between 2015 and 2023, the twin Sentinel-2 A/B satellites were used. After image pre-processing, the bathymetry was estimated using the algorithm developed by Stumpf and extraction of the coastline was conducted using the normalized difference water index (NWDI). As part of this work, four bathymetric surveys were conducted in situ in four different periods, the results of which then correlated with those of the Stumpf model applied to satellite images. The results of the regression analysis are consistent and show good correlation coefficients (R2) between 0.67 and 0.80 and root-mean-square error (RMSE) values between 0.87 m and 1.32 m, except for images captured under turbid water conditions. The maximum accretion surface is 2.12 ha to the north of the port, estimated for the period from 2018 to 2019, and 1.78 ha to the south for 2015 to 2016. The maximum erosion surface is 2.37 ha to the north of the port for the period from 2017 to 2018 and 1.16 ha to the south from 2017 to 2018. Therefore, the amplitude of accretion and erosion is greater to the north of the port than to the south. The present study demonstrates the ability of Sentinel-2 satellites to monitor silting and coastline changes in the vicinity of this port, which could help to address the effects of climate change and human activities in order to protect the marine ecosystem. [ABSTRACT FROM AUTHOR]

A sufficiently precise measurement of black hole spin is required to carry out quantitative tests of the Kerr metric and to understand several phenomena related to astrophysical black holes. After 24 yr, XTE J2012+381 again underwent an outburst in 2022 December. In this work, we focused on the measurement of the spin and mass of the black hole candidate XTE J2012+381 using broad-band spectral analysis of X-ray data from Swift/XRT and NuSTAR. Using the relxillCp model, the spin and inclination of the source were found to be |$0.883_{-0.061}^{+0.033}$| and |$46.2_{-2.0}^{+3.7}$| deg, respectively, for high disc density (⁠|$i.e.\,\,10^{20}\,\,\mathrm{cm}^{-3}$|⁠). We further test our results for lamp-post geometry using the relxilllpCp model. The spin and inclination of the source were found to be |$0.892_{-0.044}^{+0.020}$| and |$43.1_{-1.2}^{+1.4}$| deg, respectively. Then 'continuum-fitting' method was used for the soft state to estimate the mass of BH and found to be |$7.95_{-3.25}^{+7.65}\,\,\mathrm{M}_{\odot }$| and |$7.48_{-2.75}^{+5.80}\,\,\mathrm{M}_{\odot }$| for the spin and inclination estimated from the relxillCp and relxilllpCp model, respectively. We used a distance of 5.4 kpc as measured by Gaia using the parallax method. This study also addresses the issue of supersolar iron abundance in XTE J2012+381 using reflionx-based reflection model and found high disc density for the source. [ABSTRACT FROM AUTHOR]

White dwarf atmospheres are frequently polluted by material from their own planetary systems. Absorption features from Ca, Mg, Fe, and other elements can provide unique insights into the provenance of this exoplanetary material, with their relative abundances being used to infer accretion of material with core- or mantle-like composition. Across the population of white dwarfs, the distribution of compositions reveals the prevalence of geological and collisional processing across exoplanetary systems. By predicting the distribution of compositions in three evolutionary scenarios, this work assesses whether they can explain current observations. We consider evolution in an asteroid belt analogue, in which collisions between planetary bodies that formed an iron core lead to core- or mantle-rich fragments. We also consider layer-by-layer accretion of individual bodies, such that the apparent composition of atmospheric pollution changes during the accretion of a single body. Finally, we consider that compositional spread is due to random noise. We find that the distribution of Ca, Fe, and Mg in a sample of 202 cool DZs is consistent with the random noise scenario, although 7 individual systems show strong evidence of core-mantle differentiation from additional elements and/or low noise levels. Future surveys that detect multiple elements in each of a few hundred white dwarfs, with well-understood biases, have the potential to confidently distinguish between the three models. [ABSTRACT FROM AUTHOR]

Extreme mass ratio inspirals (EMRIs) are one of the primary targets for the recently adopted millihertz gravitational-wave observatory LISA. Some previous studies have argued that a fraction of all EMRIs form in matter-rich environments, and can potentially explain the dozens of soft X-ray band (⁠|$\sim 10^{-1}\,\rm keV$|⁠), low-frequency (⁠|$\sim 0.1$| mHz) periodic phenomena known as quasi-periodic eruptions (QPEs) and quasi-periodic oscillations (QPOs). Here, using a representative EMRI population retrofitted with cutoffs on LISA-band SNRs and luminosity distances to account for the sensitivity of current instruments, we estimate the mean frequency band in which QPEs and QPOs originating from detectable LISA EMRIs may be emitting an X-ray signal 'today' (i.e. in 2024) to be |$0.46 \pm 0.22$| mHz. We also model the well-known QPO source, RE J1034+396, which falls in this frequency band, as an EMRI assuming its primary black hole mass to be |$10^6{-}10^7 \,{\rm M}_\odot$|⁠. Through a prior-predictive analysis, we estimate the orbiting compact object's mass to be |$46^{+ 10}_{-40} \,{\rm M}_\odot$| and the source's LISA-band SNR as |$\approx 14$|⁠ , highlighting it as a candidate multimessenger EMRI target. We also highlight the role of current and near-future X-ray and UV observatories in enabling multimessenger observations of EMRIs in conjunction with LISA, and conclude with a discussion of caveats of the current analysis, such as the exclusion of eccentricity and inclination from the model, and the measurability of subsolar mass compact object EMRIs. [ABSTRACT FROM AUTHOR]

We have investigated whether the lack of X-ray pulsations from most neutron star (NS) low-mass X-ray binaries (LMXBs) could be due to the extension of their inner disc to the NS surface. To estimate the inner disc radii, we have employed the model, recently proposed to account for the torque reversals of LMXBs. In this model, the inner disc radius depends on the spin period as well as the dipole moment and the mass inflow rate of the disc. Our model results indicate that most LMXBs have mass accretion rates above the minimum critical rates required for the inner disc to reach down to the NS surface and thereby quench the pulsed X-ray emission. For most sources X-ray pulsations are allowed when the period decreases below a certain critical value. For the same parameters, the model is also consistent with the observed X-ray luminosity ranges of the individual accreting millisecond X-ray pulsars (AMXPs). The paucity of AMXPs compared to the majority population of non-pulsing LMXBs is explained, as well as the fact that AMXPs are transient sources. [ABSTRACT FROM AUTHOR]

We present the analysis of publicly available NuSTAR, Suzaku , and XMM–Newton observations of the symbiotic recurrent nova T CrB covering the 2006.77–2022.66 yr period. The X-ray spectra are analysed by adopting a model that includes a reflection component produced by the presence of a disc that mimics the accretion disc and the immediate surrounding medium. Our best-fitting model requires this disc to have a radius of 1 au, effective thickness of 0.1 au, averaged column density 10 |$^{25}$|  cm |$^{-2}$| and orientation of 50 |$^{\circ }$| with respect to the line of sight. This disc is about a factor of two larger than recent estimations for the accretion disc and its presence contributes significantly via reflection to the total X-ray flux detected from T CrB, which naturally produces the emission of the 6.4 keV Fe line. Our analysis suggests that the temperature of the boundary layer evolved from 14.8 keV in the steady-state phase (before 2016), to 2.8 keV in the 2017.24 epoch, to finally stabilize to about |$\sim$| 8 keV in the subsequent epochs. These variations in the plasma temperature of the boundary layer are attributed to the evolution of the mass accretion rate (⁠|$\dot{M}_\mathrm{acc}$|⁠), which is estimated to have an averaged value of |$\dot{M}_\mathrm{acc}$|  = 2.6 |$\times \,10^{-8}$|  M |$_\odot$|  yr |$^{-1}$| for the current active phase. The presence of emission lines in the XMM–Newton Reflection Grating Spectrometer spectrum of 2017.24 prevents from adopting a blackbody emission model to fit the soft X-ray range. Instead, we use plasma emission models that suggest the presence of adiabatically shocked gas produced by gas velocities of 110–200 km s |$^{-1}$|⁠ , very likely tracing jet-like ejections similar to what is found in other symbiotic systems. The analysis of X-ray and optical data together show that T CrB has a similar evolution as black hole binaries, accreting neutron stars and active galactic nuclei in the hardness–intensity diagram. [ABSTRACT FROM AUTHOR]

Jetted astrophysical phenomena with black hole engines, including binary mergers, jetted tidal disruption events, and X-ray binaries, require a large-scale vertical magnetic field for efficient jet formation. However, a dynamo mechanism that could generate these crucial large-scale magnetic fields has not been identified and characterized. We have employed three-dimensional global general relativistic magnetohydrodynamical simulations of accretion discs to quantify, for the first time, a dynamo mechanism that generates large-scale magnetic fields. This dynamo mechanism primarily arises from the non-linear evolution of the magnetorotational instability (MRI). In this mechanism, large non-axisymmetric MRI-amplified shearing wave modes, mediated by the axisymmetric azimuthal magnetic field, generate and sustain the large-scale vertical magnetic field through their non-linear interactions. We identify the advection of magnetic loops as a crucial feature, transporting the large-scale vertical magnetic field from the outer regions to the inner regions of the accretion disc. This leads to a larger characteristic size of the, now advected, magnetic field when compared to the local disc height. We characterize the complete dynamo mechanism with two time-scales: one for the local magnetic field generation, |$t_{\rm gen}$|⁠ , and one for the large-scale scale advection, |$t_{\rm adv}$|⁠. Whereas the dynamo we describe is non-linear, we explore the potential of linear mean field models to replicate its core features. Our findings indicate that traditional |$\alpha$| -dynamo models, often computed in stratified shearing box simulations, are inadequate and that the effective large-scale dynamics is better described by the shear current effects or stochastic |$\alpha$| -dynamos. [ABSTRACT FROM AUTHOR]

We provided a comprehensive study of the properties of the black hole in the low-mass X-ray binary system 4U 1543-47, specifically focusing on the 2021 outburst (MJD 59380–59470). Using observations from the Insight - HXMT mission, we employed X-ray reflection fitting method and analysed spectral data to estimate key black hole parameters. Through our investigation redbased on 6 out of the 52 available observations, we estimated the spin parameter of the black hole to be |$0.902_{-0.053}^{+0.054}$| and the inclination angle of the accretion disc to be |$28.91_{-1.24}^{+1.82}$| ° (90 per cent confidence limits, statistical only), then we discussed the influence of high luminosity. Based on the relxill series models are not suitable for thick disc scenario, and in comparison with findings from other studies, we propose that our estimation of the spin value may be exaggerated. [ABSTRACT FROM AUTHOR]

This paper investigates the accretion of neutron stars (NSs) in active galactic nucleus (AGN) accretion discs. We classify potential accretion modes of NSs in AGN discs, proposing a hierarchical model of NS accretion: accretion flow from the Bondi sphere to accretion columns. The accretion of NSs in AGN discs differs from that of BHs, especially within the scale of the NS's magnetosphere due to its hard surface and magnetic field. As the accretion flow approaches the magnetosphere, the magnetic fields guide the accretion flow to form accretion columns, primarily dominated by neutrinos. While neutrinos generated from single NS accretion may not have observable effects, considering the all-sky background, they contribute to the neutrino background in the sub-MeV energy range comparable to that of supernova explosions. NS accretion may also lead to the generation of mass quadrupole moments, consequently generating gravitational waves (GWs). The GWs, which exhibit characteristic effects like periodic modulations and echoes, could be observed by third-generation GW detectors. The emission of neutrinos and GWs carries away energy and angular momentum brought by accretion, reducing the feedback effect on the AGN disc. This results in an exceptionally high NS accretion rate, leading to a collapse time-scale shorter than the migration-merge time-scale, making it less likely that binary NS mergers originate from AGN discs. [ABSTRACT FROM AUTHOR]

Crescent-shaped asymmetries are common in millimetre observations of protoplanetary discs and are usually attributed to vortices or dust overdensities. However, they often appear on a single side of the major axis and roughly symmetric about the minor axis, suggesting a geometric origin. In this work, we interpret such asymmetries as emission from the exposed inner cavity walls of inclined discs and use them to characterize their vertical extent. Here we focus on the discs around CIDA 9 and RY Tau, first modelling their observations in visibility space with a simple geometric prescription for the walls, and then exploring more detailed radiative transfer models. Accounting for the wall emission yields significantly better residuals than purely axisymmetric models, and we estimate the dust scale height of these systems to be 0.4 au at 37 au for CIDA 9 and 0.2 au at 12 au for RY Tau. Finally, we identify crescent-shaped asymmetries in twelve discs, nine of which have constraints on their orientation – in all cases, the asymmetry appears on the far-side of the disc, lending support to the hypothesis that they are due to their inner rims. Modelling this effect in larger samples of discs will help to build a statistical view of their vertical structure. [ABSTRACT FROM AUTHOR]

A major prediction of most super-Eddington accretion theories is the presence of anisotropic emission from supercritical discs, but the degree of anisotropy and its dependence on energy remain poorly constrained observationally. A key breakthrough allowing to test such predictions was the discovery of high-excitation photoionized nebulae around ultraluminous X-ray sources (ULXs). We present efforts to tackle the degree of anisotropy of the ultraviolet/extreme ultraviolet (UV/EUV) emission in super-Eddington accretion flows by studying the emission-line nebula around the archetypical ULX NGC 1313 X–1. We first take advantage of the extensive wealth of optical/near-UV and X-ray data from Hubble Space Telescope, XMM–Newton, Swift X-ray telescope, and NuSTAR observatories to perform multiband, state-resolved spectroscopy of the source to constrain the spectral energy distribution (SED) along the line of sight. We then compare spatially resolved cloudy predictions using the observed line-of-sight SED with the nebular line ratios to assess whether the nebula 'sees' the same SED as observed along the line of sight. We show that to reproduce the line ratios in the surrounding nebula, the photoionizing SED must be a factor of ≈4 dimmer in UV emission than along the line of sight. Such nearly iosotropic UV emission may be attributed to the quasi-spherical emission from the wind photosphere. We also discuss the apparent dichotomy in the observational properties of emission-line nebulae around soft and hard ULXs, and suggest that only differences in mass-transfer rates can account for the EUV/X-ray spectral differences, as opposed to inclination effects. Finally, our multiband spectroscopy suggests that the optical/near-UV emission is not dominated by the companion star. [ABSTRACT FROM AUTHOR]

The fundamental plane of black hole activity is a very important tool to study accretion and jets. However, we found that the SEDs of AGNs and XRBs are different in the 2–10 keV energy band, and it seems inappropriate to use 2–10 keV X-ray luminosities to study the fundamental plane. In this work, we use the luminosity near the peak of the blackbody radiation of the active galactic nuclei and black hole binaries to replace the 2–10 keV luminosity. We re-explore the fundamental plane of black hole activity by using the 2500 A ˚ luminosity as the peak luminosity of the blackbody radiation of AGNs and 1 keV luminosity as the peak luminosity of the blackbody radiation of XRBs. We compile samples of black hole binaries and active galactic nuclei with luminosity near the peak luminosity of blackbody radiation and study the fundamental plane between radio luminosity ( L R ), the peak luminosity of blackbody radiation ( L peak ), and black hole mass ( M BH ). We find that the radio–peak luminosity correlations are L 5 GHz / L Edd ∝ (L 2500 A ˚ / L Edd) 1.55 and L 5 GHz / L Edd ∝ (L 1 keV / L Edd) 1.53 for AGN and XRB, respectively, in the radiatively efficient sample, and L 5 GHz / L Edd ∝ (L 2500 A ˚ / L Edd) 0.48 and L 5 GHz / L Edd ∝ (L 1 keV / L Edd) 0.53 in the radiatively inefficient sample, respectively. Based on the similarities in radio–peak correlations, we further propose a fundamental plane in radio luminosity, the peak luminosity of blackbody radiation, and black hole mass, which is radiatively efficient: log L 5 GHz = 1. 57 − 0.01 + 0.01 log L peak − 0. 32 − 0.16 + 0.16 log M BH − 27. 73 − 0.34 + 0.34 with a scatter of σ R = 0.48 dex, and radiatively inefficient: log L 5 GHz = 0. 45 − 0.01 + 0.01 log L peak + 0. 91 − 0.10 + 0.12 log M BH + 12. 58 − 0.38 + 0.38 with a scatter of σ R = 0.63 dex. Our results are similar to those of previous studies on the fundamental plane for radiatively efficient and radiatively inefficient black hole activity. However, our results exhibit a smaller scatter, so when using the same part of blackbody radiation (i.e., the peak luminosity of the blackbody radiation), the fundamental plane becomes a little bit tighter. [ABSTRACT FROM AUTHOR]

Binary black holes (BBHs) embedded within the accretion disks that fuel active galactic nuclei (AGN) are promising progenitors for the source of gravitational wave (GW) events detected by LIGO/VIRGO. Several recent studies have shown that when these binaries form, they are likely to be highly eccentric and retrograde. However, many uncertainties remain concerning the orbital evolution of these binaries as they either inspiral toward merger or disassociate. Previous hydrodynamical simulations exploring their orbital evolution have been predominantly two-dimensional or have been restricted to binaries on nearly circular orbits. We present the first high-resolution, three-dimensional local shearing-box simulations of both prograde and retrograde eccentric BBHs embedded in AGN disks. We find that retrograde binaries shrink several times faster than their prograde counterparts and exhibit significant orbital eccentricity growth, the rate of which monotonically increases with binary eccentricity. Our results suggest that retrograde binaries may experience runaway orbital eccentricity growth, which may bring them close enough together at pericenter for GW emission to drive them to coalescence. Although their eccentricity is damped, prograde binaries shrink much faster than their orbital eccentricity decays, suggesting they should remain modestly eccentric as they contract toward merger. Finally, binary precession driven by the AGN disk may dominate over precession induced by the supermassive black hole depending on the binary accretion rate and its location in the AGN disk, which can subdue the evection resonance and von Ziepel–Lidov–Kozai cycles. [ABSTRACT FROM AUTHOR]

The present work studies the spectral properties of some X-ray point sources in the galaxies NGC 4382 and NGC 1399 as observed by Chandra in different epochs. Five point sources from the galaxy NGC 4382 and twelve point sources from the galaxy NGC 1399 with net source count ≥ 100 were considered for the present work. Spectra of all the seventeen sources were fitted with two empirical models—the absorbed power law and an absorbed disk black body. Most of the sources were found to be equally well explained by both the models except for a few of them which prefers one model over the other. While most of the sources are found to be in the Ultraluminous hard state ( L x ≥ 10 39 erg s - 1 ; powerlaw photon index ( Γ) ∼ 2.0 /kT in > 1.0 keV), for which inverse comptonization of soft photons may be responsible for their emission. Significantly, we found spectral state transitions in two sources - NGC 4382 X-1 & NGC 1399 X-8. Long-term variability in luminosity were also observed in the sources -NGC 4382 X-1, NGC 1399 X-7, NGC 1399 X-8, NGC 1399 X-9 & NGC 1399 X-17. While most of the ULXs here are found to be powered by accretion on to stellar mass black holes, there is one super-soft ULX (NGC 1399 X-9) with k T in ∼ 0.36 keV and bolometric luminosity, L x ∼ 2.69 × 10 39 erg s - 1 , which in one of the epoch, was found to be consistent with harboring Intermediate mass black hole (IMBH) with M BH ∼ 200 - 67 + 62 M ⊙ , accreting at 0.09 times the Eddington limit. However, another two soft ULXs - NGC 1399 X-10 with k T in ∼ 0.66 keV and NGC 1399 X-15 with k T in ∼ 0.53 keV with their corresponding estimated bolometric luminosities were found to be consistent with harboring stellar mass blackholes accreting within their Eddington limit. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of shoreline change is essential for efficient coastal management. This research provides a thorough analysis of the long-term changes to the shoreline in the Tamil Nadu district of Tirunelveli, India, spanning five decades (1972–2022). Remote sensing techniques and digital shoreline analysis techniques were employed to investigate the temporal variations and underlying mechanisms influencing shoreline dynamics. Remote sensing methods include satellite imagery analysis, digital shoreline analysis techniques involve GIS-based mapping and measurement of coastal features. The statistical methods like EPR, LRR and NSM techniques were used in this study to identify the shoreline changes. It considers the sedimentary structures of tidal flats and grain size investigations in the region to improve our comprehension of the geological characteristics and sediment dynamics driving shoreline alterations. The findings demonstrate how the shoreline location at Koodankulam changed considerably during the course of the research. This study report spans a sizable length of time and provides significant insights on the long-term behaviour of the Tirunelveli district coastline. Sedimentary structures and grain size investigations provide insights into erosion, deposition patterns, and sediment transport, crucial for understanding shoreline dynamics. The three primary very high erosion hotspots in the research area are Kunjanvilai, Koodankulam, and Kuttam. At a rate of − 23.5, − 23.6, and − 23.6 m/year, maximum erosion is shown by EPR, LRR, and WLR. This study outcomes major two regions like Vijayapathi and Anjugramam are facing more accretion zone. A maximum of 13.33, 11.14, and 11.14 m/year is shown by EPR, LRR, and WLR. According to projection research, the spans will measure 60.67 km in 2042 and 59.62 km in 2032, respectively. [ABSTRACT FROM AUTHOR]

Many high-state cataclysmic variables (CVs) exhibit blue-shifted absorption features in their ultraviolet (UV) spectra – a smoking-gun signature of outflows. However, the impact of these outflows on optical spectra remains much more uncertain. During its recent outburst, the eclipsing dwarf nova V455 And displayed strong optical emission lines whose cores were narrower than expected from a Keplerian disc. Here, we explore whether disc + wind models developed for matching UV observations of CVs can also account for these optical spectra. Importantly, V455 And was extremely bright at outburst maximum: the accretion rate implied by fitting the optical continuum with a standard disc model is |$\dot{M}_{\rm acc} \simeq 10^{-7}~{\rm M}_\odot ~{\rm yr^{-1}}$|⁠. Allowing for continuum reprocessing in the outflow helps to relax this constraint. A disc wind can also broadly reproduce the optical emission lines, but only if the wind is (i) highly mass-loaded, with a mass-loss rate reaching |$\dot{M}_{\rm wind} \simeq 0.4 \dot{M}_{\rm acc}$|⁠ , and/or (ii) clumpy, with a volume filling factor |$f_V \simeq 0.1$|⁠. The same models can describe the spectral evolution across the outburst, simply by lowering |$\dot{M}_{\rm acc}$| and |$\dot{M}_{\rm wind}$|⁠. Extending these models to lower inclinations and into the UV produces spectra consistent with those observed in face-on high-state CVs. We also find, for the first time in simulations of this type, P-Cygni-like absorption features in the Balmer series, as have been observed in both CVs and X-ray binaries. Overall, dense disc winds provide a promising framework for explaining multiple observational signatures seen in high-state CVs, but theoretical challenges persist. [ABSTRACT FROM AUTHOR]

Gravitational radiation alone is not efficient in hardening the orbit of a wide binary black hole (BBH). By employing a toy model for the interstellar medium (ISM) surrounding BBHs, here we discuss the effect of this baryonic medium on BBH dynamics. Depending on the BBH's mass, we show that a binary surrounded by an isotropic cold neutral medium (i.e. an asymptotic temperature |$T_{\infty } \approx 100$|  K) with a time-averaged particle density of |$\langle n_\mathrm{ H} \rangle = \mathcal {O}(1)$|  cm |$^{-3}$| can play a significant role in hardening the binary orbit over a |$\mathcal {O}(10^9)$|  yr time-scale. Additionally, this causes the black hole's mass to grow at a rate |${\propto} m^2$|⁠. We thus discuss the impact of the ISM on the LIGO-Virgo-KAGRA (LVK) observables and quantify the properties of the ISM under which the latter could act as an additional important pathway for driving a subset of LVK's BBH mergers. [ABSTRACT FROM AUTHOR]

We investigate the properties of circumstellar discs (CDs) produced in hydrodynamical simulations of gravoturbulent core collapse considering Kolmogorov and Burger-type turbulence. We report that massive discs are more prevalent in the Kolmogorov regime than for Burger-type turbulence. A significant number of discs are formed with a radius of ∼15 au in both cases. However, the number of extended discs with radii >15 au is significantly larger in case of Kolmogorov turbulence. The two regimes of turbulence, in general, yield disc radii in the ranges of 7−30 au and 13−39 au, respectively. The corresponding ranges of the disc masses are 30.37 M Jup−0.92 M⊙ and 2.09  M Jup−0.13 M⊙, respectively. Moreover, the ratio M disc/ M star is higher in models of Kolmogorov-type turbulence than in models of Burgers-type turbulence. We do not find any correlation between R disc and M disc over the explored range of initial temperatures (8−14 K) and the type of turbulence. Also, for these initial thermal variations, the turbulent CD structures do not exhibit signs of turbulent diffusion. Nonetheless, both sub- and supersonic velocity dispersions cause variations in the specific angular momentum of infalling gas, especially for CDs with radii ∼ 16−21 au. The radial profiles of CDs do not correlate with the initial conditions. [ABSTRACT FROM AUTHOR]

We observed the low-mass X-ray binary Cyg X-2 for a total of 18 nights over two observing runs in July and September of 2006, using the Otto Struve Telescope at McDonald Observatory and the Rossi X-ray Timing Explorer. Using discrete cross-correlations, we found peaks occurring at near-zero lags in the flaring branch of the colour–colour diagram, which could signify reprocessing, in addition to an anticorrelation within the normal branch. When comparing optical flux to the system's placement on the Z track, two distinct behaviours were seen: (1) a state with no correlation, and (2) a multivalued (horizontal and normal branches)/correlated (flaring branch) state. The correlation was the result of direct steps and more gradual falls to and from the flaring branch, respectively. Finally, we modelled timed spectra with 64 s bins with an extended accretion disc corona model. We found that correlations occurred between the optical and the various fitted parameters, particularly the blackbody normalization (and blackbody radius by extension) in higher intensity regions. Despite this, the Z track location was found to be a far better predictor of physical parameters than the optical flux, with clean correlations seen in every branch of the Z track. Where optical correlations are found, the location on the Z track was a better predictor of optical flux than any individual physical parameter. [ABSTRACT FROM AUTHOR]

Supermassive black hole binaries (SMBHBs) are natural by-products of galaxy mergers and are expected to be powerful multimessenger sources. They can be powered by the accretion of matter and then radiate across the electromagnetic spectrum, much like normal active galactic nuclei (AGNs). Current electromagnetic observatories have a good chance of detecting and identifying these systems in the near future. However, precise observational indicators are needed to distinguish individual AGNs from SMBHBs. In this paper, we propose a novel electromagnetic signature from SMBHBs: non-thermal emission produced by the interaction between the jets ejected by the black holes. We study close SMBHBs, which accrete matter from a circumbinary disc and the mini-discs formed around each hole. Each black hole ejects a magnetically dominated jet in the direction of its spin through the Blandford–Znajek mechanism. We argue that in such a situation, the interaction between the jets can trigger strong magnetic reconnection events, where particles are accelerated and emit non-thermal radiation. Depending on whether the jets are aligned or misaligned, this radiation can have different periodicities. We model the evolution of the particles accelerated during the dual jet interaction and calculate their radiative output, obtaining spectra and providing estimates for the variability time-scales. We finally discuss how this emission compares with that of normal AGNs. [ABSTRACT FROM AUTHOR]

We investigate the formation of dust traffic jams in polar-aligning circumbinary discs. We use 3D smoothed particle hydrodynamical simulations of both gas and dust to model an initially highly misaligned circumbinary disc around an eccentric binary. As the circumbinary disc evolves to a polar configuration (perpendicular to the binary orbital plane), the difference in the precession between the gas and dust produces dust traffic jams, which become dense dust rings. We find the formation of dust rings exists for different Stokes number, binary eccentricity, and initial disc tilt. Dust rings are only produced while the circumbinary disc is misaligned to the binary orbital plane. When the disc becomes polar aligned, the dust rings are still present and long-lived. Once these dust rings are formed, they drift inward. The drift time-scale depends on the Stokes number. The lower the Stokes number, the faster the dust ring drifts near the inner edge of the disc. The dust rings will have an increased mid-plane dust-to-go ratio, which may be a favourable environment for the steaming instability to operate. [ABSTRACT FROM AUTHOR]

It is well established that supermassive black hole (SMBH) feedback is crucial for regulating the evolution of massive, if not all, galaxies. However, modelling the interplay between SMBHs and their host galaxies is challenging due to the vast dynamic range. Previous simulations have utilized simple subgrid models for SMBH accretion, while recent advancements track the properties of the unresolved accretion disc, usually based on the thin α-disc model. However, this neglects accretion in the radiatively inefficient regime, expected to occur through a thick disc for a significant portion of an SMBH's lifetime. To address this, we present a novel 'unified' accretion disc model for SMBHs, harnessing results from the analytical advection-dominated inflow–outflow solution (ADIOS) model and state-of-the-art general relativistic (radiation-)magnetohydrodynamics (GR(R)MHD) simulations. Going from low to high Eddington ratios, our model transitions from an ADIOS flow to a thin α-disc via a truncated disc, incorporating self-consistently SMBH spin evolution due to Lense–Thirring precession. Utilizing the moving mesh code arepo , we perform simulations of single and binary SMBHs within gaseous discs to validate our model and assess its impact. The disc state significantly affects observable luminosities, and we predict markedly different electromagnetic counterparts in SMBH binaries. Crucially, the assumed disc model shapes SMBH spin magnitudes and orientations, parameters that gravitational wave observatories like LISA and IPTA are poised to constrain. Our simulations emphasize the importance of accurately modelling SMBH accretion discs and spin evolution, as they modulate the available accretion power, profoundly shaping the interaction between SMBHs and their host galaxies. [ABSTRACT FROM AUTHOR]

Accretion discs are fundamental to much of astronomy. They can occur around stars, both young and old, around compact objects they provide a window into the extremes of physics, and around supermassive black holes in galaxy centres, they generate spectacular luminosities that can outshine the entire galaxy. However, our understanding of the inner workings of accretion discs remains far from complete. Here, we revisit a conundrum in the observations of some of the simplest accreting systems: the cataclysmic variables (CVs). The high-accretion-rate states of (non-magnetic) CVs can be divided into the short-lived outbursts (∼a week), typical of dwarf novae (DNe), and the long-lived (and sometimes perpetual) high states of nova-like (NL) CVs. Since both sorts of high-state occur in approximately steady-state accretion discs with similar properties and accretors, we would expect them to display similar spectral energy distributions. However, previous analyses based on UV spectra from the International Ultraviolet Explorer have shown that their spectral energy distributions are different. We perform a re-analysis of the data using up to date calibrations and distance (and thus dereddening) estimates to test whether this difference persists and whether it is statistically significant over the sample. We find that it does persist, and it is statistically significant. We propose routes to investigating this discrepancy further and discuss the implications this has for other accreting systems, such as X-ray binaries, active galactic nuclei, and protoplanetary discs. [ABSTRACT FROM AUTHOR]

Context. The recent 230 GHz observations from the Event Horizon Telescope (EHT) collaboration are able to image the innermost structure of the M87 galaxy showing the shadow of the black hole, a photon ring, and a ring-like structure that agrees with thermal synchrotron emission from the accretion disc. However, at lower frequencies, M87 is characterized by a large-scale jet with clear signatures of nonthermal emission. It is necessary to explore the impacts of nonthermal emission on black hole shadow images and extended jets, especially at lower frequencies. Aims. In this study, we aim to compare models with different electron heating prescriptions to one another and to investigate how these prescriptions and nonthermal electron distributions may affect black hole shadow images and the broadband spectrum energy distribution (SED) function. Methods. We performed general relativistic radiative transfer (GRRT) calculations in various two-temperature general relativistic magnetohydrodynamic (GRMHD) models utilizing different black hole spins and different electron heating prescriptions coupled with different electron distribution functions (eDFs). Results. Through a comparison with GRRT images and SEDs, we found that when considering a variable κ eDF, the parameterized prescription of the R − β electron temperature model with Rh = 1 is similar to the model with electron heating in the morphology of images, and the SEDs at a high frequency. This is consistent with previous studies using the thermal eDF. However, the nuance between them could be differentiated through the diffuse extended structure seen in GRRT images, especially at a lower frequency, and the behavior of SEDs at low frequency. The emission from the nearside jet region is enhanced in the case of electron heating provided by magnetic reconnection and it will increase if the contribution from the regions with stronger magnetization is included or if the magnetic energy contribution to κ eDF mainly in the magnetized regions is considered. Compared with the thermal eDF, the peaks of the SEDs shift to a lower frequency when we consider nonthermal eDF. [ABSTRACT FROM AUTHOR]

The Neutron Star Interior Composition Explorer (NICER) monitoring campaign of Cyg X-1 allows us to study its spectral-timing behavior at energies < 1 keV across all states. The hard state power spectrum can be decomposed into two main broad Lorentzians with a transition at around 1 Hz. The lower-frequency Lorentzian is the dominant component at low energies. The higher-frequency Lorentzian begins to contribute significantly to the variability above 1.5 keV and dominates at high energies. We show that the low- and high-frequency Lorentzians likely represent individual physical processes. The lower-frequency Lorentzian can be associated with a (possibly Comptonized) disk component, while the higher-frequency Lorentzian is clearly associated with the Comptonizing plasma. At the transition of these components, we discover a low-energy timing phenomenon characterized by an abrupt lag change of hard (≳2 keV) with respect to soft (≲1.5 keV) photons, accompanied by a drop in coherence, and a reduction in amplitude of the second broad Lorentzian. The frequency of the phenomenon increases with the frequencies of the Lorentzians as the source softens and cannot be seen when the power spectrum is single-humped. A comparison to transient low-mass X-ray binaries shows that this feature does not only appear in Cyg X-1, but that it is a general property of accreting black hole binaries. In Cyg X-1, we find that the variability at low and high energies is overall highly coherent in the hard and intermediate states. The high coherence shows that there is a process at work which links the variability, suggesting a physical connection between the accretion disk and Comptonizing plasma. This process fundamentally changes in the soft state, where strong red noise at high energies is incoherent to the variability at low energies. [ABSTRACT FROM AUTHOR]

Context. Accreting black hole sources show variable outflows at different mass scales. For instance, in the case of galactic nuclei, our own Galactic center Sgr A* exhibits flares and outbursts in the X-ray and infrared bands. Recent studies suggest that the inner magnetospheres of these sources have a pronounced effect on these emissions. Aims. Accreting plasma carries the frozen-in magnetic flux along with it down to the black hole horizon. During the infall, the magnetic field intensifies, and this can lead to a magnetically arrested state. We investigate the competing effects of inflows at the black hole horizon and the outflows that develop in the accreting plasma through the action of the magnetic field in the inner magnetosphere, and we determine the implications of these effects. Methods. We started with a spherically symmetric Bondi-type inflow and introduced a magnetic field. In order to understand the influence of the initial configuration, we started the computations with an aligned magnetic field with respect to the rotation axis of the black hole. Then we proceeded to the case of magnetic fields that are inclined to the rotation axis of the black hole. We employed the 2D and 3D versions of the code HARM for the aligned field models and used the 3D version for the inclined field. We compared the results of computations with each other. Results. We observe that the magnetic lines of force start to accrete with the plasma while an equatorial intermittent outflow develops. This outflow continues to push some material away from the black hole in the equatorial plane, while some other material is ejected in the vertical direction from the plane. In consequence, the accretion rate fluctuates as well. The direction of the black hole spin prevails at later stages. It determines the flow geometry near the event horizon. On larger scales, however, the flow geometry remains influenced by the initial inclination of the field. [ABSTRACT FROM AUTHOR]

The detection of a high-velocity (∼0.3 c) inflow of highly ionized matter during an extended XMM–Newton observation of the luminous Seyfert galaxy PG1211+143 in 2014 provided the first direct evidence of a short-lived accretion event, and an explanation for the powerful winds (UFOs) now recognized as a common property of many luminous Seyfert galaxies. Although the ultra-fast inflow observed at a redshift of 0.483 was detected in only one of seven spacecraft orbits, weaker (lower column) but more persistent absorption is seen at a redshift of 0.123 in the high-exposure soft X-ray (RGS) spectra summed over all seven individual spacecraft orbits. Similar stacking of the higher energy (pn camera) spectra reveals underlying absorption at a redshift of 0.148. Interpreted, conventionally, as a Doppler redshift, the RGS observation indicates a line-of-sight inflow velocity v ∼ 0.038 c and (free-fall) radial location at 1400  Rg , with the higher redshift and ionization in pn camera spectra perhaps detecting that inflow closer to the black hole. A very different explanation would be absorption in matter subject to the strong gravity close to the SMBH, an interpretation supported by the launch of a new UFO in the final spacecraft orbit. [ABSTRACT FROM AUTHOR]

Accreting binary white dwarf systems are among the sources expected to emanate gravitational waves that the Laser Interferometer Space Antenna (LISA) will detect. We investigate how accurately the binary parameters may be measured from LISA observations. We complement previous studies by performing our parameter estimation on binaries containing a low-mass donor with a thick, hydrogen-rich envelope. The evolution is followed from the early, pre-period minimum stage, in which the donor is non-degenerate, to a later, post-period minimum stage with a largely degenerate donor. We present expressions for the gravitational-wave amplitude, frequency, and frequency derivative in terms of white dwarf parameters (masses, donor radius, etc.), where binary evolution is driven by gravitational-wave radiation and accretion torques, and the donor radius and logarithmic change in radius (ηd) due to mass-loss are treated as model parameters. We then perform a Fisher analysis to reveal the accuracy of parameter measurements, using models from Modules for Experiments in Stellar Astrophysics (mesa) to estimate realistic fiducial values at which we evaluate the measurement errors. We find that the donor radius can be measured relatively well with LISA observations alone, while we can further measure the individual masses if we have an independent measurement of the luminosity distance from electromagnetic observations. When applied to the parameters of the recently discovered white dwarf binary ZTF J0127+5258, our Fisher analysis suggests that we will be able to constrain the system's individual masses and donor radius using LISA 's observations, given Zwicky Transient Facility's (ZTF's) measurement of the luminosity distance. [ABSTRACT FROM AUTHOR]

We report on the detection of type-C quasi-periodic oscillations during the initial stages of the outburst of Swift J1727.8–1613 in 2023. Using data of the INTEGRAL observatory along with the data of the Mikhail PavlinskyART-XC telescope on board Spektr-RG and X-ray Telescope (XRT) of the Neil Gehrels Swift observatory the fast growth of the quasi-periodic oscillations (QPO) frequency was traced. We present a hard X-ray light curve that covers the initial stages of the 2023 outburst – the fast rise and plateau – and demonstrate that the QPO frequency was stable during the plateau. The switching from type-C to type-B QPO was detected with the beginning of the source flaring activity. We have constructed a broad-band spectrum of Swift J1727.8−1613 and found an additional hard cutoff power-law spectral component extending at least up to 250 keV. Finally, we have obtained an upper limit on the hard X-ray flux at the beginning of the optical outburst and estimated the delay of the hard X-ray outburst with respect to the optical one. [ABSTRACT FROM AUTHOR]