Search

Multi-epoch Chandra and XMM–Newton observations of the symbiotic system R Aquarii (R Aqr) spanning 22 yr are analysed by means of a reflection model produced by an accretion disc. This methodology helps dissecting the contribution from different components in the X-ray spectra of R Aqr: the soft emission from the jet and extended emission, the heavily extinguished plasma component of the boundary layer and the reflection contribution, which naturally includes the 6.4 keV Fe fluorescent line. The evolution with time of the different components is studied for epochs between September 2000 and December 2022, and it is found that the fluxes of the boundary layer and that of the reflecting component increase as the stellar components in R Aqr approach periastron passage, a similar behaviour is exhibited by the shocked plasma produced by the precessing jet. Using publicly available optical and UV data we are able to study the evolution of the mass-accretion rate |$\dot{M}_\mathrm{acc}$| and the wind accretion efficiency |$\eta$| during periastron. These exhibit a small degree of variability with median values of |$\dot{M}_\mathrm{acc}$| =7.3 |$\times 10^{-10}$|  M |$_\odot$|  yr |$^{-1}$| and |$\eta$| =7 |$\times 10^{-3}$|⁠. We compare our estimations with predictions from a modified Bondi–Hoyle–Lyttleton accretion scenario. [ABSTRACT FROM AUTHOR]

Changing-look active galactic nuclei (CLAGNs) are characterized by extreme variations in line emission over short time-scales, mostly affecting broad H  |$\beta$| lines. While a few hundred CLAGNs are known, a complete sample of turn-on CLAGNs is still elusive. Here, we present a search for turn-on CLAGNs in a complete sample of galaxies, using archival spectra and recent light curves. We obtained light curves from the Asteroid Terrestrial Impact Last Alert System for 16 232 emission-line galaxies, including both star-forming and active galaxies, at |$z< 0.1$| with spectra from the Six-degree Field Galaxy Survey (6dFGS). We first establish typical variability behaviour for different active galactic nucleus (AGN) types, as recorded between 2001 and 2009, and then select outliers from the bulk behaviour as CLAGN candidates. We obtain new spectra for the candidates and identify 12 new turn-on CLAGNs (appearing broad H  |$\beta$| line) and 19 new turn-off CLAGNs (disappearing broad H  |$\beta$| line). We may have missed AGNs that changed and reverted their state over the 15–20 yr since 6dFGS spectra were taken, and thus our CLAGN rates of 1.7 per cent for turn-on and 9.6 per cent for turn-off are lower limits. The turn-on rate is naturally much lower as the type 1.9/2 sample is dominated by obscured AGNs due to orientation, which is not expected to change. However, the number of turn-on (27) and turn-off (24) CLAGNs we find are similar, suggesting that our parent AGN sample is reasonably complete in our search volume at |$z < 0.1$|⁠. [ABSTRACT FROM AUTHOR]

MAXI J1803-298 is a transient black hole candidate discovered in 2021 May during an outburst that lasted several months. Multiple X-ray observations reveal recurring "dipping" intervals in several of its light curves, particularly during the hard/intermediate states, with a typical recurrence period of ∼7 hr. We report analysis of four NuSTAR observations of the source, supplemented with NICER data where available, over the duration of the outburst evolution covering the hard, intermediate, and the soft states. Reflection spectroscopy reveals the black hole to be rapidly spinning (a * = 0.990 ± 0.001) with a near edge-on viewing angle (i = 70° ± 1°). Additionally, we show that the light-curve dips are caused by photoelectric absorption from a moderately ionized absorber whose origin is not fully understood, although it is likely linked to material from the companion star impacting the outer edges of the accretion disk. We further detect absorption lines in some of the spectra, potentially associated with Fe xxv and Fe xxvi, indicative of disk winds with moderate to extreme velocities. During the intermediate state and just before transitioning into the soft state, the source showed a sudden flux increase, which we found to be dominated by soft disk photons and consistent with the filling of the inner accretion disk, at the onset of state transition. In the soft state, we show that models of disk self-irradiation provide a better fit and a preferred explanation to the broadband reflection spectrum, consistent with previous studies of other accreting sources. [ABSTRACT FROM AUTHOR]

Radio galaxies are a subclass of active galactic nuclei that drive relativistic jets from their center and are observed in radio to very-high-energy gamma rays. The emission mechanisms and regions are still unknown. High-energy gamma rays can be explained by the emission from the magnetically arrested disks (MADs) around the central supermassive black hole (BH), for which the magnetic flux threading the BH is in a saturation level, although the emission from the MADs does not explain the optical and X-ray data. We construct a two-zone multiwavelength emission model in which optical and X-rays come from jets, while millimeter/submillimeter and gamma rays come from MADs. Our model takes into account the particle injection by the magnetic reconnection at the jet base close to the BH and particle entrainment from the ambient gas at the jet emission zone. We apply our model to M87 and find that our model can explain the simultaneous multiwavelength data, except for the radio data, which could be explained if we extend our one-zone emission model to a one-dimensional one. We also find that the strong plasma entrainment is necessary to explain the multiwavelength data. Our model will be tested by variability analysis among the multiwavelength data. [ABSTRACT FROM AUTHOR]

Although ultraluminous X-ray pulsars (ULXPs) are believed to be powered by super-Eddington accretion onto a magnetized neutron star (NS), the detailed structures of the inflow–outflow and magnetic fields are still not well understood. We perform general relativistic radiation magnetohydrodynamics (GR-RMHD) simulations of super-Eddington accretion flows onto a magnetized NS with dipole and/or quadrupole magnetic fields. Our results show that an accretion disk and optically thick outflows form outside the magnetospheric radius, while inflows aligned with magnetic field lines appear inside. When the dipole field is more prominent than the quadrupole field at the magnetospheric radius, accretion columns form near the magnetic poles, whereas a quadrupole magnetic field stronger than the dipole field results in the formation of a belt-like accretion flow near the equatorial plane. The NS spins up as the angular momentum of the accreting gas is converted into the angular momentum of the electromagnetic field, which then flows into the NS. Even if an accretion column forms near one of the magnetic poles, the observed luminosity is almost the same on both the side with the accretion column and the side without it, because the radiation energy is transported to both sides through scattering. Our model suggests that galactic ULXP Swift J0243.6+6124 has a quadrupole magnetic field of 2 × 1013 G and a dipole magnetic field of less than 4 × 1012 G. [ABSTRACT FROM AUTHOR]

Volcanic sequences of bimodal basalt–trachyte–alkaline rhyolite character with alkaline granites are widespread in central Mongolia. They crop out in small sublatitudinal grabens scattered along the southern and western surroundings of the Khentey part of the Mongol–Okhotsk Belt. According to geochronological data, the bimodal magmatic activity continued from the latest Triassic to earliest Jurassic (at ∼220–195 Ma). Many rocks of the bimodal sequences contain high concentrations of alkalis and rare metals. Fractional crystallization was the leading process for enrichment of rare metals up to their ore-level concentrations in the most differentiated melts. Mafic magmas enriched relative to the OIB in most incompatible trace elements were parental for all rocks of these associations. At the same time, they show elevated Ba and depleted Ta and Nb contents, which indicate that a lithospheric mantle component was involved in their source. The Nd and Sr isotopic ratios of the rocks indicate that the magmas were derived from at least two sources, which are identified as enriched asthenospheric mantle and metasomatized subduction-modified lithospheric mantle. Bimodal magmatism in the Khentey segment of the Mongol–Okhotsk belt appeared ~30 Ma after collision caused by the closure of the Ada-Tsag branch of the Mongol–Okhotsk Ocean at about 250 Ma. Rifting affected the entire surroundings of the Khentey segment of the belt and controlled this magmatism. It was initiated by the collapse of the orogen with delamination of its keel caused the involvement of asthenospheric mantle in the Late Triassic–Early Jurassic magmatism of the region [ABSTRACT FROM AUTHOR]

Young star-forming regions in massive environments are ideal test beds to study the influence of surroundings on the evolution of discs around low-mass stars. We explore two distant young clusters, IC 1848-East and West located in the massive W5 complex. These clusters are unique due to their similar (distance, age and extinction) yet distinct (stellar density and far-ultraviolet radiation fields) physical properties. We use deep multiband photometry in optical, near-infrared and mid-infrared wavelengths complete down to the substellar limit in at least five bands. We trace the spectral energy distribution of the sources to identify the young pre-main sequence members in the region and derive their physical parameters. The disc fraction for the East and West clusters down to 0.1 M |$_\odot$| was found to be |$\sim 27\,\pm$| 2 per cent (N |$_\mathrm{disc}$|  = 184, N |$_\mathrm{discless}$|  = 492) and |$\sim 17\,\pm$| 1 per cent (N |$_\mathrm{disc}$|  = 173, N |$_\mathrm{discless}$|  = 814), respectively. While no spatial variation in the disc fraction is observed, these values are lower than those in other nearby young clusters. Investigating the cause of this decrease, we find a correlation with the intense feedback from massive stars throughout the cluster area. We also identified the disc sources undergoing accretion and observed the mass accretion rates to exhibit a positive linear relationship with the stellar host mass and an inverse relationship with stellar age. Our findings suggest that the environment significantly influences the dissipation of discs in both clusters. These distant clusters, characterized by their unique attributes, can serve as templates for future studies in outer galaxy regions, offering insights into the influence of feedback mechanisms on star and planetary formation. [ABSTRACT FROM AUTHOR]

This paper examines the oscillatory behaviour of relativistic, non-self-gravitating, charged-fluid toroidal structures within the context of the Kerr metric. The primary objective is to explore how thick accretion discs influence the mass and spin measurements of black holes and neutron stars in low-mass X-ray binaries (LMXBs) through quasi-periodic oscillations (QPOs) models. To achieve this, we conduct a local analysis within a general relativistic framework, determining the radial epicyclic and orbital frequencies in a perfect fluid disc. The tori are modelled using a non-Keplerian distribution of specific angular momentum, and we analyse how the oscillation properties depend on the model's angular momentum distribution parameters. Subsequently, we connect these oscillatory frequencies to high-frequency QPOs observed in LMXBs, enabling us to calculate the optimal mass and spin values for each studied source. [ABSTRACT FROM AUTHOR]

With data observed by the Hard X-ray Modulation Telescope (Insight - HXMT) and the Neutron star Interior Composition Explorer (NICER), we study low-frequency quasi-periodic oscillations (QPOs) of the black hole candidate MAXI J1803−298 during the 2021 outburst. Based on the hardness–intensity diagram and the difference in the QPOs properties, type-C and type-B QPOs are found in the low-hard state and soft-intermediate state, respectively. After searching for and classifying QPOs in the Fourier domains, we extract the QPO component and study it with wavelet analysis. The QPO and no-QPO time intervals are separated by the confidence level, so that the S-factor, which is defined as the ratio of the QPO time interval to the total length of the good time interval, is calculated. We found S-factors decrease with QPOs frequency for type-C QPOs but stay stable around zero for type-B QPOs. The relation of S-factor of type-C QPOs and photon energy and the correlation of S-factor and counts are also studied. Different correlations between the S-factor and counts for different energy bands indicate different origins of QPOs in high- and low-energy bands, which may be due to a dual-corona scenario. [ABSTRACT FROM AUTHOR]

A neutron star (NS) accreting matter from a companion star in a low-mass X-ray binary (LMXB) system can spin up to become a millisecond pulsar (MSP). Properties of many such MSP systems are known, which is excellent for probing fundamental aspects of NS physics when modelled using the theoretical computation of NS LMXB evolution. Here, we systematically compute the long-term evolution of NS, binary, and companion parameters for NS LMXBs using the stellar evolution code mesa. We consider the baryonic to gravitational mass conversion to calculate the NS mass evolution and show its cruciality for the realistic computation of some parameters. With computations using many combinations of parameter values, we find the general nature of the complex NS spin frequency (⁠|$\nu$|⁠) evolution, which depends on various parameters, including accretion rate, fractional mass-loss from the system, and companion star magnetic braking. Further, we utilize our results to precisely match some main observed parameters, such as |$\nu$|⁠ , orbital period (⁠|$P_{\rm orb}$|⁠), etc. of four accreting millisecond X-ray pulsars (AMXPs). By providing the |$\nu$|⁠ , |$P_{\rm orb}$|⁠ , and the companion mass spaces for NS LMXB evolution, we indicate the distribution and plausible evolution of a few other AMXPs. We also discuss the current challenges in explaining the parameters of AMXP sources with brown dwarf companions and indicate the importance of modelling the transient accretion in LMXBs as a possible solution. [ABSTRACT FROM AUTHOR]

We present a broadband spectral analysis of the soft-intermediate and soft states using Insight-HXMT observations of the black hole binary MAXI J1348–630 during its outburst in 2019. We employ a combination of reflection and continuum fitting methods to measure the spin of the black hole and determine a spin of a = 0.79 ± 0.13, which is consistent with most of the previous results. Additionally, we investigate some sources of systematic uncertainty that could bias the measurement. The valid spectral hardening factor can partially account for the spin evolution observed during the outburst. Other potential factors, such as assumptions about the corona's structure and their interaction with reflected photons, can also affect the accuracy of spin measurements. Furthermore, our analysis reveals that MAXI J1348–630 exhibits a significantly high disk density (∼1022 cm−3), with a moderate iron abundance of approximately 2.5 times solar. [ABSTRACT FROM AUTHOR]

The accretion flow onto a neutron star will be impacted by irradiation from a type I X-ray burst. The burst radiation exerts Poynting–Robertson (PR) drag on the accretion disk, leading to an enhanced mass accretion rate. Observations of X-ray bursts often find evidence that the normalization of the disk-generated persistent emission (commonly denoted by the factor f a ) increases during a burst, and changes in f a have been used to infer the evolution of the mass accretion rate due to PR drag. Here, we examine this proposed relationship between f a and mass accretion rate enhancement using time-resolved data from simulations of accretion disks impacted by type I X-ray bursts. We consider bursts from both spinning and nonspinning neutron stars and track both the change in accretion rate due to PR drag and the disk emission spectra during the burst. Regardless of the neutron star spin, we find that f a strongly correlates with the disk temperature and only weakly follows the mass accretion rate (the Pearson correlation coefficients are ≤0.63 in the latter case). Additionally, heating causes the disk to emit at higher energies, reducing its contribution to a soft excess. We conclude that f a cannot accurately capture the mass accretion rate enhancement and is rather a tracer of the disk temperature. [ABSTRACT FROM AUTHOR]

The accretion/ejection processes in T Tauri stars are fundamental to their physical evolution, while also impacting the properties and evolution of the circumstellar material at a time when planet formation takes place. To date, the characterization of ongoing accretion processes in stellar pairs at 5–50 au scales has been challenging as high-angular resolution spectrographs are required to extract the spectral features of each component. We present the analysis of spectroscopic observations of the tight (160 mas, 25 au) T Tauri system HT Lup A/B, obtained with MUSE at the Very Large Telescope in 2021 March and July. We focus on constraining the accretion/ejection processes and variability of the secondary component HT Lup B by searching for accretion tracers by applying high-resolution spectral differential imaging techniques. We retrieve strong (signal-to-noise ratio > 5) H α, H β, and [O i ] λ 6300 emission in both epochs. The H α and H β line fluxes showcase high variability, with variations up to 200%–300% between epochs. The fluxes are consistent with accretion rates of 3× 10−9 M ⊙ yr−1 and 8 × 10−10 M ⊙ yr−1 for the first and second epochs, respectively. We attribute the increased accretion activity during the first night to a "burst-like" event, followed by a relaxation period more representative of the common accretion activity of the system. The [O i ] λ 6300 line profiles remain relatively similar between epochs and suggest ejection rates on the order of 10−9−10−10 M ⊙ yr−1, compatible with moderate disk wind emission. Our results also indicate that the accretion processes of HT Lup B are compatible with Classical T Tauri stars, unlike previous classifications. [ABSTRACT FROM AUTHOR]

We present the tidal disruption event (TDE) AT2022lri, hosted in a nearby (≈144 Mpc) quiescent galaxy with a low-mass massive black hole (104 M ⊙ < M BH < 106 M ⊙). AT2022lri belongs to the TDE-H+He subtype. More than 1 Ms of X-ray data were collected with NICER, Swift, and XMM-Newton from 187 to 672 days after peak. The X-ray luminosity gradually declined from 1.5 × 1044 erg s−1 to 1.5 × 1043 erg s−1 and remains much above the UV and optical luminosity, consistent with a super-Eddington accretion flow viewed face-on. Sporadic strong X-ray dips atop a long-term decline are observed, with a variability timescale of ≈0.5 hr–1 days and amplitude of ≈2–8. When fitted with simple continuum models, the X-ray spectrum is dominated by a thermal disk component with inner temperature going from ∼146 to ∼86 eV. However, there are residual features that peak around 1 keV, which, in some cases, cannot be reproduced by a single broad emission line. We analyzed a subset of time-resolved spectra with two physically motivated models describing a scenario either where ionized absorbers contribute extra absorption and emission lines or where disk reflection plays an important role. Both models provide good and statistically comparable fits, show that the X-ray dips are correlated with drops in the inner disk temperature, and require the existence of subrelativistic (0.1–0.3 c) ionized outflows. We propose that the disk temperature fluctuation stems from episodic drops of the mass accretion rate triggered by magnetic instabilities or/and wobbling of the inner accretion disk along the black hole's spin axis. [ABSTRACT FROM AUTHOR]

We examine expected effective spin (⁠|$\chi _{{\rm eff},1{\rm yr}}$|⁠) and orbital eccentricity (⁠|$e_{1\rm yr}$|⁠) correlations for a population of observable equal-mass massive black hole binaries (MBHBs) with total redshifted mass |$M_z\sim [10^{4.5},10^{7.5}]~{{\rm M}_{\odot }}$| embedded in a circumbinary disc (CBD) at redshifts |$z=1$| and |$z=2$|⁠ , 1 yr before merging in the Laser Interferometer Space Antenna (LISA) band. We find a strong correlation between measurable eccentricity and negative effective spin for MBHBs that are carried to merger by retrograde accretion. This is due to the well-established eccentricity pumping of retrograde accretion and less-well-established formation of retrograde mini-discs coupled with a stable retrograde CBD throughout the binary evolution from the self-gravitating radius. Conversely, prograde accretion channels result in positive |$\chi _{{\rm eff},1\rm yr}$| and non-measurable |$e_{1\rm yr}$| except for almost unity Eddington ratio and |$M_z\lesssim 10^{5}~{{\rm M}_{\odot }}$| MBHBs at |$z=1$|⁠. This clear contrast between the two CBD orientations – and particularly the unique signature of retrograde configurations – provides a promising way to unlock the mysteries of MBHB formation channels in the LISA era. [ABSTRACT FROM AUTHOR]

We investigate the formation of dust traffic jams in polar-aligning circumbinary discs. In our first paper, we found as the circumbinary disc evolves towards a polar configuration perpendicular to the binary orbital plane, the differential precession between the gas and dust components leads to multiple dust traffic jams. These dust traffic jams evolve to form a coherent dust ring. In part two, we use 3D smoothed particle hydrodynamical simulations of gas and dust to model an initially highly misaligned circumbinary disc around the 99 Herculis (99 Her) binary system. Our results reveal that the formation of these dust rings is observed across various disc parameters, including the disc aspect ratio, viscosity, surface density power-law index, and temperature power-law index. The dust traffic jams are long-lived and persist even when the disc is fully aligned polar. The midplane dust-to-gas ratio within the rings can surpass unity, which may be a favourable environment for planetesimal formation. Using 2D inviscid shearing box calculations with parameters from our 3D simulations, we find streaming instability modes with significant growth rates. The streaming instability growth time-scale is less than the tilt oscillation time-scale during the alignment process. Therefore, the dust ring will survive once the gas disc aligns polar, suggesting that the streaming instability may aid in forming polar planets around 99 Her. [ABSTRACT FROM AUTHOR]

We present an analytic, quasi-local model for accretion discs threaded by net, vertical magnetic flux. In a simple slab geometry and ignoring stochastic mean-field dynamo effects, we calculate the large-scale field resulting from the balance between kinematic field amplification and turbulent diffusion. The ability of the disc to accumulate magnetic flux is sensitive to a single parameter dependent on the ratio of the vertical diffusion time to the Alfvén crossing time, and we show how the saturation levels of magnetorotational and other instabilities can govern disc structure and evolution. Under wide-ranging conditions, inflow is governed by large-scale magnetic stresses rather than internal viscous stress. We present models of such 'magnetically boosted' discs and show that they lack a radiation pressure-dominated zone. Our model can account for 'magnetically elevated' discs as well as instances of midplane outflow and field reversals with height that have been seen in some global simulations. Using the time-dependent features of our model, we find that the incorporation of global transport effects into disc structure can lead to steady or episodic 'magnetically arrested discs' that maximize the concentration of magnetic flux in their central regions. [ABSTRACT FROM AUTHOR]

Almost all accreting black hole and neutron star (NS) X-ray binary systems (XRBs) exhibit prominent brightness variations on a few characteristic time-scales and their harmonics. These quasi-periodic oscillations (QPOs) are thought to be associated with the precession of a warped accretion disc, but the physical mechanism that generates the precessing warp remains uncertain. Relativistic frame dragging (Lense–Thirring precession) is one promising candidate, but a misaligned magnetic field is an alternative, especially for NS XRBs. Here, we report the discovery of five accreting white dwarf systems (AWDs) that display strong optical QPOs with characteristic frequencies and harmonic structures that suggest they are the counterpart of the QPOs seen in XRBs. Since AWDs are firmly in the classical (non-relativistic) regime, Lense–Thirring precession cannot account for these QPOs. By contrast, a weak magnetic field associated with the white dwarf can drive disc warping and precession in these systems, similar to what has been proposed for NS XRBs. Our observations confirm that magnetically driven warping is a viable mechanism for generating QPOs in disc-accreting astrophysical systems, certainly in AWDs and possibly also in NS XRBs. Additionally, they establish a new way to estimate magnetic field strengths, even in relatively weak-field systems where other methods are not available. [ABSTRACT FROM AUTHOR]

Comprehensive spectrotemporal analyses of the Z-type neutron star low-mass X-ray binary GX 5−1 were performed using 10 broad-band observations from AstroSat /Soft X-ray Telescope and Large Area X-ray Proportional Counter (LAXPC) instruments. The LAXPC-20 hardness–intensity diagram showed horizontal and normal branches (HBs and NBs) of the Z track which exhibited secular motion. The time-averaged spectra in the energy range 0.7–25.0 keV could be fitted with the model combination – |$\tt {constant}\, \times \, \tt {tbabs}\, \times \, \tt {edge}\, \times \, \tt {edge}\, \times \, \tt {thcomp}\, \times \, \tt {diskbb}$|⁠. This yielded |$\Gamma \, \sim$| 2, |$kT_{\mathrm{ e}}\, \sim$| 3.3 keV, and |$F_{\mathrm{ disc}}$| / |$F_{\mathrm{ total}}\, \sim$| 0.8 indicating the soft/intermediate spectral state of the source during the observations. Flux-resolved spectral analysis revealed a positive correlation between |$kT_{\mathrm{ in}}$| and |$F_{\mathrm{ bol}}$|⁠. However, a negative correlation was observed between them in one of the NBs. Time-averaged temporal analysis revealed multiple HB oscillations (HBOs) and NB oscillations (NBOs), and peaked noise components in the |$\sim$| 5–50 Hz range. Furthermore, flux-resolved temporal analysis showed that the frequency of the HBOs correlates positively whereas the strength of HBOs correlates negatively with |$F_{\mathrm{ bol}}$|⁠ , indicating their probable origin from the accretion disc. In contrast, the frequency and strength of NBOs remain fairly constant with |$F_{\mathrm{ bol}}$|⁠ , suggesting that they originate from a different region in the system. Using the relativistic precession model along with highest frequency of the HBO, the upper limits of the magnetic dipole moment (⁠|$\mu$|⁠) and field strength (B) at the poles of the neutron star in the system were found to be 25.60 |$\times \, 10^{25}$| G cm3 and 3.64 |$\times \, 10^{8}$| G, respectively, for |$k_{\mathrm{ A}}$| = 1. [ABSTRACT FROM AUTHOR]

Parsec-scale separation supermassive black hole binaries in the centre of gas-rich galaxy merger remnants could be surrounded by massive circumbinary discs (CBDs). Black hole mass and spin evolution during the gas-rich binary inspiral are crucial in determining the direction and power of relativistic jets that radio observations with LOFAR (Low-Frequency Array) and SKAO (Square Kilometer Array Observatory) will probe, and for predicting gravitational wave (GW) emission that the IPTA (International Pulsar Timing Array) and LISA (Laser Interferometer Space Antenna) will measure. We present 3D hydrodynamic simulations capturing gas-rich, self-gravitating CBDs around a |$2\times 10^6$| M |$_{\odot }$| supermassive black hole binary, that probe different mass ratios, eccentricities, and inclinations. We employ a subgrid Shakura–Sunyaev accretion disc to self-consistently model black hole mass and spin evolution together with super-Lagrangian refinement techniques to resolve gas flows, streams, and mini-discs within the cavity, which play a fundamental role in torquing and feeding the binary. We find that higher mass ratio and eccentric binaries result in larger cavities, while retrograde binaries result in smaller cavities. All of the simulated binaries are expected to shrink with net gravitational torques being negative. Unlike previous simulations, we do not find preferential accretion onto the secondary black hole. This implies smaller chirp masses at coalescence and hence a weaker GW background. Critically this means that spin alignment is faster than the binary inspiral time-scale even for low-mass ratios. When considering initially misaligned systems, the orientation of the mini-discs around each black hole can vary significantly. We discuss the implications of this behaviour for black hole spin alignment and highlight the need for broader parameter space studies of misaligned systems to understand the impact on black hole recoil velocities. [ABSTRACT FROM AUTHOR]

We propose that the ring structure found by the Event Horizon Telescope Collaboration (EHTC) as the black hole shadow of Sgr A* is an artefact caused by the bumpy point spread function (PSF) of the EHT 2017 data. The imaging using sparse u-v  data requires detailed scrutiny of the PSF. The estimated shadow diameter (⁠|$\mathrm{48.7\pm 7~\mu \rm as}$|⁠) is equal to the spacing between the main beam and the first sidelobe of the PSF (⁠|$\mathrm{49.09~\mu \rm as}$|⁠), which immediately suggests a potential problem in the deconvolution of the PSF. We show that the ring image can be derived from non-ring simulated data sets (noise only; point source) with a narrow field-of-view (FOV) and an assumed self-calibration, suggesting that the EHT 2017 u-v  coverage is insufficient for reliable imaging. The EHTC analysis, based on calibrations with assumptions about the source's size and properties, selected the final image by prioritizing the appearance rate of a similar structure from a large imaging parameter space over data consistency. Our independent analysis with conventional hybrid mapping reveals an elongated east–west structure, consistent with previous observations. We believe it to be more reliable than the EHTC image, owing to half the residuals in normalized visibility amplitude. The eastern half is brighter, possibly due to a Doppler boost from the rapidly rotating disc. We hypothesize that our image shows a portion of the accretion disc from about 2 to a few R S (where R S is the Schwarzschild radius) away from the black hole, rotating with nearly |$\mathrm{60~{{\ \rm per\ cent}}}$| of the speed of light and viewed from an angle of 40°−45°. [ABSTRACT FROM AUTHOR]

The characteristic timescale at which the variability of active galactic nuclei (AGNs) turns from red noise to white noise can probe the accretion physics around supermassive black holes (SMBHs). A number of works have studied the characteristic timescale of quasars and obtained quite different scaling relations between the timescale and quasar physical properties. One possible reason for the discrepancies is that the characteristic timescale can be easily underestimated if the light curves are not long enough. In this work, we construct well-defined AGN samples to observationally test the relationships between the characteristic timescale and AGN properties obtained by previous works. Our samples eliminate the effects of insufficient light-curve lengths. We confirm that the timescale predictions of the Corona Heated Accretion disk Reprocessing model are consistent with our timescale measurements. The timescale predictions by empirical relations are systematically smaller than our measured ones. Our results provide further evidence that AGN variability is driven by thermal fluctuations in SMBH accretion disks. Future flagship time-domain surveys can critically test our conclusions and reveal the physical nature of AGN variability. [ABSTRACT FROM AUTHOR]

We present a comprehensive study of the spectral properties of the accreting millisecond X-ray pulsar IGR J17498−2921 during its 2023 outburst. Similar to other accreting millisecond X-ray pulsars, the broadband spectral emission observed quasi-simultaneously by NICER and NuSTAR is well described by an absorbed Comptonized emission with an electron temperature of ∼17 keV plus a disk reflection component. The broadening of the disk reflection spectral features, such as a prominent iron emission line at 6.4–6.7 keV, is consistent with the relativistic motion of matter in a disk truncated at ∼21 Rg from the source, near the Keplerian corotation radius. From the high-cadence monitoring data obtained with NICER, we observed that the evolution of the photon index and the temperature of seed photons tracks variations in the X-ray flux. This is particularly evident close to a sudden ∼–0.25 cycle jump in the pulse phase, which occurs immediately following an X-ray flux flare and a drop in the pulse amplitude below the 3σ detection threshold. We also report on the non-detection of optical pulsations with TNG/SiFAP2 from the highly absorbed optical counterpart. [ABSTRACT FROM AUTHOR]

Context. EX Lupi is the prototype of EX Lup-type stars, which are classical T Tauri stars (cTTSs) with luminosity bursts and outbursts of 1–5 magnitudes that last for a few months to a few years. These events are ascribed to an episodic accretion that can occur repeatedly, but whose physical mechanism is still debated. Aims. We aim to investigate the magnetically driven accretion of EX Lup in quiescence. We include for the first time a study of the small- and large-scale magnetic field. This allows us to characterise the magnetospheric accretion process of the system completely. Methods. We used spectropolarimetric times series acquired in 2016 and 2019 with the Echelle SpectroPolarimetric Device for the Observation of Stars and in 2019 with the SpectroPolarimètre InfraRouge at the Canada-France-Hawaii telescope during a quiescence phase of EX Lup. We were thus able to perform a variability analysis of the radial velocity, the emission lines, and the surface-averaged longitudinal magnetic field in different epochs and wavelength domains. We also provide a small-scale magnetic field analysis using Zeeman intensification of photospheric lines and a large-scale magnetic topology reconstruction using Zeeman-Doppler imaging. Results. Our study reveals that typical magnetospheric accretion is ongoing on EX Lup. A main accretion funnel flow connects the inner disc to the star in a stable fashion and produces an accretion shock on the stellar surface close to the pole of the magnetic dipole component. We also measure one of the strongest fields ever observed on cTTSs. This strong field indicates that the disc is truncated by the magnetic field close to but beyond the corotation radius, where the angular velocity of the disc equals the angular velocity of the star. This configuration is suitable for a magnetically induced disc instability that yields episodic accretion onto the star. [ABSTRACT FROM AUTHOR]

Context. The Spektrum-Roentgen-Gamma (SRG)/extended Roentgen Survey with an Imaging Telescope Array (eROSITA) All-Sky Survey (eRASS) is expected to contain ∼100 quasars that emitted their light when the universe was less than a billion years old, that is, at z > 5.6. By selection, these quasars populate the bright end of the active galactic nuclei (AGN) X-ray luminosity function, and their space density offers a powerful demographic diagnostic of the parent super-massive black hole (SMBH) population. Aims. Of the ⪆400 quasars that have been discovered at z > 5.6 to date, less than 15% have been X-ray detected. We present a pilot survey to uncover the elusive X-ray luminous end of the distant quasar population. Methods. We have designed a quasar selection pipeline based on optical, infrared and X-ray imaging data from DES DR2, VHS DR5, CatWISE2020 and the eRASS (up to its four-pass cumulative version, eRASS:4). The core selection method relies on SED template fitting. We performed optical follow-up spectroscopy with the Magellan/LDSS3 instrument for the redshift confirmation of a subset of candidates. We have further obtained a deeper X-ray image of one of our candidates with Chandra ACIS-S. Results. We report the discovery of five new quasars in the redshift range 5.6 < z < 6.1. Two of these quasars are detected in eRASS and are, therefore, X-ray ultra-luminous by selection. We also report the detection of these quasars at radio frequencies. The first one is a broad absorption line quasar, which shows significant, order-of-magnitude X-ray dimming over 3.5 years, corresponding to six months in the quasar rest frame. The second X-ray detected quasar is a jetted source with compact morphology. We show that a blazar configuration is likely for this source, making it one of the most distant blazars known to date. Conclusions. With our pilot study, we demonstrate the power of eROSITA as a discovery machine for luminous quasars in the epoch of reionization. The X-ray emission of the two eROSITA detected quasars are likely to be driven by different high-energetic emission mechanisms, a diversity which we will further explore in a future systematic full-hemisphere survey. [ABSTRACT FROM AUTHOR]

Context. S26 is an extragalactic microquasar with the most powerful jets ever discovered. They have a kinetic luminosity of Lj ∼ 5 × 1040 erg s−1. This implies that the accretion power to the black hole should be super-Eddington, of the order of Lacc ∼ Lj. However, the observed X-ray flux of this system indicates an apparent very sub-Eddington accretion luminosity of LX ≈ 1037 erg s−1. Aims. We aim to characterize the nature of S26, explain the system emission, and study the feasibility of super-Eddington microquasars as potential PeVatron sources. Methods. We first analyze multi-epoch X-ray observations of S26 obtained with XMM-Newton and model the super-Eddington disk and its wind. We then develop a jet model and study the particle acceleration and radiative processes that occur in shocks generated near the base of the jet and in its terminal region. Results. We find that the discrepancy between the jet and the apparent disk luminosities in S26 is caused by the complete absorption of the disk radiation by the wind ejected from the super-Eddington disk. The nonthermal X-rays are produced near the base of the jet, and the thermal X-rays are emitted in the terminal regions. The radio emission observed with the Australia Telescope Compact Array can be explained as synchrotron radiation produced at the reverse shock in the lobes. We also find that S26 can accelerate protons to PeV energies in both the inner jet and the lobes. The ultra-high energy protons accelerated in the lobes of S26 are injected into the interstellar medium with a total power of ∼1036 erg s−1. Conclusions. We conclude that S26 is a super-Eddington microquasar with a dense disk-driven wind that obscures the X-ray emission from the inner disk, and that the supercritical nature of the system allows the acceleration of cosmic rays to PeV energies. [ABSTRACT FROM AUTHOR]

Context. The connection between quasi-periodic oscillations (QPOs) and magnetic fields has been investigated in various celestial bodies. Magnetohydrodynamic (MHD) waves have been employed to explain the simultaneous upper and lower kilohertz (kHz) QPOs. Nevertheless, the intricate and undefined formation pathways of twin kHz QPOs present a compelling avenue for exploration. This study area holds great interest as it provides an opportunity for deriving crucial parameters related to compact stars. Aims. We strive to develop a self-consistent model elucidating the radiation mechanism of twin kHz QPOs, which we then compare it with observations. Methods. A sample of 28 twin kHz QPOs detected from the X-ray binary 4U 1636–53 was used for a comparison with the results of the Markov chain Monte Carlo calculations based on our model of the radiation mechanism of twin kHz QPOs, which is related to twin MHD waves. Results. We obtained 28 groups of parameters of 4U 1636–53 and a tight exponential fit between the flux and the temperature of seed photons to Compton up-scattering and find that the electron temperature in the corona around the neutron star decreases with increasing seed photon temperature. Conclusions. The origin of twin kHz QPOs are dual disturbances that arise from twin MHD waves that are generated at the innermost radius of an accretion disc. The seed photons can be transported through a high temperature corona and are Compton up-scattered. The photons that vary the frequencies of twin MHD waves lead to the observed twin kHz QPOs. [ABSTRACT FROM AUTHOR]

The four characteristic oscillation frequencies of accretion flows (in addition to the Keplerian orbital frequency) are often discussed in the context of the time variability of black hole and neutron star (NS) low-mass X-ray binaries (LMXBs). These four frequencies are the frequencies of the axisymmetric radial and vertical epicyclic oscillations, and the frequencies of non-axisymmetric oscillations corresponding to the periastron (radial) and Lense-Thirring (vertical) precessions. In this context, we investigated the effect of the quadrupole moment of a slowly rotating NS and provide complete formulae for calculating these oscillation and precession frequencies, as well as convenient approximations. Simple formulae corresponding to the geodesic limit of a slender torus (and test-particle motion) and the limit of a marginally overflowing torus (a torus exhibiting a critical cusp) are presented, and more general approximate formulae are included to allow calculations for arbitrarily thick tori. We provide the Wolfram Mathematica code used for our calculations together with the C++ and PYTHON codes for calculating the frequencies. Our formulae can be used for various calculations regarding the astrophysical signatures of the NS super-dense matter equation of state. For instance, we demonstrate that even for a given fixed number of free parameters, a model that accounts for fluid flow precession matches the frequencies of twin-peak quasiperiodic oscillations observed in NS LMXBs better than a model that uses geodesic precession. [ABSTRACT FROM AUTHOR]

We present a full general relativistic analytic solution for a radiation-pressure-supported equilibrium fluid torus orbiting a rotating neutron star (NS). We applied previously developed analytical methods that include the effects of both the NS's angular momentum and quadrupole moment in the Hartle-Thorne geometry. The structure, size, and shape of the torus are explored, with a particular focus on the critically thick solution – the cusp tori. For the astrophysically relevant range of NS parameters, we examined how our findings differ from those obtained for the Schwarzschild space-time. The solutions for rotating stars display signatures of an interplay between relativistic and Newtonian effects where the impact of the NS angular momentum and quadrupole moment are almost counterbalanced at a given radius. Nevertheless, the space-time parameters still strongly influence the size of tori, which can be shown in a coordinate-independent way. Finally, we discuss the importance of the size of the central NS which determines whether or not a surrounding torus exists. We provide a set of tools in a Wolfram Mathematica code, which establishes a basis for further investigation of the impact of the NSs' super-dense matter equation of state on the spectral and temporal behaviour of accretion tori. [ABSTRACT FROM AUTHOR]

GRS 1716–249 is a stellar-mass black hole in a low-mass X-ray binary that underwent a giant outburst in 2016–17. In this paper, we use simultaneous observations from the Hard X-ray Modulation Telescope (Insight-HXMT) and the Nuclear Spectroscopic Telescope Array (NuSTAR) to determine its basic parameters. The observations were performed during the softest part of the outburst and the spectra show clear thermal disk emission and reflection features. We fit the X-ray energy spectra using the joint fitting method of the continuum and reflection components with the kerrbb2 + relxill model. Since there is a possibility that the distance to this source was previously underestimated, we used the latest distance parameter of 6.9 kpc in our study, in contrast to previous works, where the distance was set at 2.4 kpc. Through a spectral fitting of the black hole mass at 6.4 M⊙, we observe a strong dependence of the derived spin on the distance: a* = 0.972−0.005+0.004 at an assumed distance of 2.4 kpc and a∗ = 0.464−0.007+0.016 at an assumed distance of 6.9 kpc, at a confidence level of 90%. When considering the uncertainties in the distance and black hole mass, there will be a wider range of spin with a*< 0.78. The fitting results with the new distance indicate that GRS 1716–249 harbors a moderate spin black hole with an inclined (i ∼ 40 − 50°) accretion disk around it. Additionally, we have also found that solely using the method of reflection component fitting, while ignoring the constraints on the spin from the accretion disk component will result in an extremely high spin. [ABSTRACT FROM AUTHOR]

Context. The gravitational lens system SDSS J1004+4112 was the first known example of a quasar lensed by a galaxy cluster. The interest in this system has been renewed following the publication of r-band light curves spanning 14.5 years and the determination of the time delays between the four brightest quasar images. Aims. We constrained the quasar accretion disk size and the fraction of the lens mass in stars using the signature of microlensing in the quasar image light curves. Methods. We built the six possible histograms of microlensing magnitude differences between the four quasar images and compared them with simulated model histograms, using a χ2 test to infer the model parameters. Results. We infer a quasar disk half-light radius of R1/2 = (0.70 ± 0.04)RE = (6.4 ± 0.4) √M/0.3M⊙ light-days at 2407 Å in the rest frame and stellar mass fractions at the quasar image positions of αA > 0.059, αB = 0.056+0.021-0.027, αC = 0.030+0.031-0.021, and αD = 0.072+0.034-0.016. Conclusions. The inferred disk size is broadly compatible with most previous estimates, and the stellar mass fractions are within the expected ranges for galaxy clusters. In the region where image C lies, the stellar mass fraction is compatible with a stellar contribution from the brightest cluster galaxy, galaxy cluster members, and intracluster light, but the values at images B, D, and especially A are slightly larger, possibly suggesting the presence of extra stellar components. [ABSTRACT FROM AUTHOR]

The structure of the accretion flow on to supermassive black holes is not well understood. Standard disc models match to zeroth-order in predicting substantial energy dissipation within optically thick material producing a characteristic strong blue/ultraviolet continuum. However, they fail at reproducing more detailed comparisons to the observed spectral shapes along with their observed variability. Based on stellar mass black holes within our Galaxy, accretion discs should undergo a transition into an X-ray hot, radiatively inefficient flow, below a (mass scaled) luminosity of |$\sim 0.02\, L_{\rm {Edd}}$|⁠. While this has been seen in limited samples of nearby low-luminosity active galactic nuclei (AGN) and few rare changing-look AGN, it is not at all clear whether this transition is present in the wider AGN population across cosmic time. A key issue is the difficulty in disentangling a change in spectral state from increased dust obscuration and/or host galaxy contamination, effectively drowning out the AGN emission. Here, we use the new eROSITA eFEDS Survey to identify unobscured AGN from their X-ray emission, matched to excellent optical imaging from Subaru's Hyper Suprime-Cam; allowing the subtraction of the host galaxy contamination. The resulting, uncontaminated, AGN spectra reveal a smooth transition from a strongly disc-dominated state in bright AGN, to the collapse of the disc into an inefficient X-ray plasma in the low-luminosity AGN, with the transition occurring at |$\sim 0.02\, L_{\rm {Edd}}$|⁠ ; revealing fundamental aspects of accretion physics in AGN. [ABSTRACT FROM AUTHOR]

This study utilizes the simultaneous broad-band observations of 4U 1735−44 from AstroSat , offering enhanced spectral and temporal resolution, to investigate its spectral properties, temporal behaviour, and burst characteristics. Spectral, type I X-ray burst, and temporal analyses on 4U 1735−44 were performed using AstroSat /Soft X-ray Telescope and Large Area X-ray Proportional Counter (LAXPC) observations. The hardness–intensity diagram from LAXPC-20 showed a positive correlation between hardness and intensity, with a pattern resembling the banana branch typical of atoll sources. Spectral analysis carried out in the 0.7–20.0 keV energy range, using the model combination – |$\tt {constant}$| |$\times$| |$\tt {tbabs}$| (⁠|$\tt {nthcomp}$| |$+$| |$\tt {diskbb}$| |$+$| |$\tt {bbodyrad}$|⁠), suggested a cool accretion disc truncated at a large distance from the neutron star in the system. Time-resolved spectral studies of two type I X-ray bursts detected from the source revealed evidence of photospheric radius expansion, allowing for an estimation of the source distance. Temporal analysis showed the presence of low-frequency quasi-periodic oscillation at |$\sim$| 69 Hz (3.3 |$\sigma$| significance with more than 99 per cent confidence) and prominent noise features below 30 Hz. [ABSTRACT FROM AUTHOR]

We investigate the effect of the cutting-edge circumbinary disc (CBD) evolution models on massive black hole binary (MBHB) populations and the gravitational wave background (GWB). We show that CBD-driven evolution leaves a tell-tale signature in MBHB populations, by driving binaries towards an equilibrium eccentricity that depends on the binary mass ratio. We find high orbital eccentricities (⁠|$e_{\rm b} \sim 0.5$|⁠) as MBHBs enter multimessenger observable frequency bands. The CBD-induced eccentricity distribution of MBHB populations in observable bands is independent of the initial eccentricity distribution at binary formation, erasing any memory of eccentricities induced in the large-scale dynamics of merging galaxies. Our results suggest that eccentric MBHBs are the rule rather than the exception in upcoming transient surveys, provided that CBDs regularly form in MBHB systems. We show that the GWB amplitude is sensitive to CBD-driven preferential accretion onto the secondary, resulting in an increase in GWB amplitude |$A_{\rm yr^{-1}}$| by over 100 per cent with just 10 per cent Eddington accretion. As we self-consistently allow for binary hardening and softening, we show that CBD-driven orbital expansion does not diminish the GWB amplitude, and instead increases the amplitude by a small amount. We further present detection rates and population statistics of MBHBs with |$M_{\rm b} \gtrsim 10^6 \, {\rm M}_{\odot }$| in Laser Interferometer Space Antenna , showing that most binaries have equal mass ratios and can retain residual eccentricities up to |$e_{\rm b} \sim 10^{-3}$| due to CBD-driven evolution. [ABSTRACT FROM AUTHOR]

A ringed accretion disc (RAD) models a cluster of axis-symmetric co-rotating and/or counter-rotating tori orbiting in the equatorial plane of a central Kerr supermassive black hole. We discuss the time evolution of such a ringed disc within the general relativity framework. Our analysis presents a study of the evolving RAD properties using a thin-disc scheme and solving a diffusion-like evolution equation for a RAD in the Kerr space–time. In the first stage of evolution, there is the inter–disc interaction where the individual rings spread inwardly and outwardly, levelling the structure and forming a single distribution with maximum density determined by the initial spread of the component rings. Time-scales are dependent on viscosity prescriptions. The early time luminosity, dominated by the dynamics of the inner ringed structure, shows a clear mark of the inner ringed structure. The RAD eventually reaches a single disc phase, building accretion to the inner edge regulated by the inner edge boundary conditions. The late-time luminosity associated with the ringed disc follows a power law decline for the final single disc. In the sideline of this analysis, we also considered a modified prescription mimicking an effective turbulent viscosity in the early phases of the rings evolutions. [ABSTRACT FROM AUTHOR]

The gravitational wave signature of a binary black hole (BBH) merger is dependent on its component mass and spin. If such black holes originate from rapidly rotating progenitors, the large angular momentum reserve in the star could drive a collapsar-like supernova explosion, hence substantially impacting these characteristics of the black holes in the binary. To examine the effect of stellar rotation on the resulting black hole mass and spin, we conduct a one-dimensional general relativistic study of the end phase of the stellar collapse. We find that the resulting black hole mass at times differs significantly from the previously assumed values. We quantify the dependence of the black hole spin magnitude on the hydrodynamics of the accretion flow, providing analytical relations for calculating the mass and spin based on the progenitor's pre-collapse properties. Depending on the nature of the accretion flow, our findings have implications for the black hole upper mass gap resulting from pair-instability supernovae, the maximum mass of a maximally rotating stellar black hole, and the maximum effective spin of a BBH formed in a tidally locked helium star–black hole binary. [ABSTRACT FROM AUTHOR]

The processes responsible for the isotopic compositions and abundances of volatile elements in the early solar system remain highly debated. Orders of magnitude variation of (highly) volatile elements exist between different magmatic iron meteorite groups, but it is unclear to what extent their depletions can be explained by evaporation from metal melts during parent body accretion and/or subsequent break up. To this end, we present 86 new evaporation experiments with the aim of constraining the volatility of most volatile metals from metallic melts. The results confirm the previously proposed important effects of S in metal melt on the volatility of the elements of interest governed by their S-loving or S-phobic behavior. Nominally S-loving elements In, Sn, Te, Pb and Bi are significantly more volatile in Fe melt relative to FeS liquid, whereas nominally S-avoiding elements Ga and Sb are more volatile in FeS liquid relative to Fe melt, at a given pressure and temperature. The newly derived volatility sequences for S-free/poor and S-rich metallic melts were also compared with commonly used volatility models based on condensation temperatures. The results indicate significant differences between the latter, including the much more volatile behavior of Te, relative to Se, in both explored bulk compositions, which are traditionally assumed to be equally volatile. The (minimum) degree of volatile element depletion due to evaporation was quantified using the new experimental results and models. A comparison between the volatile element depletions in magmatic iron meteorites and the predicted depletions appropriate for evaporation from Fe melts shows that the latter depletions can be easily reconciled with (an) evaporation event(s). Altogether, the new data and models will provide an important framework when more accurate and precise estimates of magmatic iron meteorite bulk volatile element contents are available. [ABSTRACT FROM AUTHOR]

The origin of volatile elements, the timing of their accretion and their distribution during Earth's differentiation are fundamental aspects of Earth's early evolution. Here, we present the result of a newly developed accretion and core formation model, which features the results of high P–T metal–silicate partitioning experiments. The model includes well-studied reference elements (Fe, Ni, Ca, Al, Mg, Si) as well as trace elements (V, Ga, Ag, Au, S) covering a wide range from refractory to volatile behavior. The accretion model simulates the different steps of planet formation, such as the effects of continuous, heterogenous core formation at high P–T, the effect of the Moon-forming giant impact and the addition of matter after the core formation was completed, the so-called "late veneer". To explore the "core formation signature" of the volatile depletion patterns and the quantitative influence of a late veneer, we modeled planets that would have formed from known materials, such as CI, CM, CV, CO, EH and EL meteorites, and from a hypothetical volatile depleted material, CI*. Some of the resulting planets are Earth-like in key properties, such as overall core size, major element composition, oxygen fugacity and trace element composition. The model predicts the chemical signatures of the main planetary reservoirs, the metallic core and bulk silicate planet (BSP) of the modeled planets, which we compare with the chemical signature of Earth derived previously from core formation models and mass balance-based approaches. We show that planets accreted from volatile depleted carbonaceous chondrites (CM, CV, CO and CI*) are closest in terms of major element (Si, Mg, Fe, Ca, Al, Ni) and also siderophile volatile element (Ge, Ga, Au) concentrations to the components from which Earth accreted. Chalcophile volatile elements (S, Ag), instead, require an additional process to lower their concentrations in the BSP to Earth-like concentrations, perhaps the late segregation of a sulfide melt. [ABSTRACT FROM AUTHOR]

Sea-level rise (SLR) is one of the greatest future threats to mangrove forests. Mangroves have kept up with or paced past SLR by maintaining their forest floor elevation relative to sea level through root growth, sedimentation, and peat development. Monitoring surface elevation change (SEC) or accretion rates allows us to understand mangrove response to SLR and prioritizes resilient ecosystems for conservation or vulnerable ecosystems for restoration. We compared three methods to measure SEC and accretion in mangrove forests: 210Pb, surface elevation tables (SETs), and a terrestrial light detection and ranging system (compact biomass LiDAR—CBL). Lead-210 accretion rates were not significantly different than SET SEC rates and differences between the two methods (− 2 to 2 mm/year) were within the error of our measurements. Lead-210 only measures accretion in the upper meter of sediment and cannot capture deeper subsurface processes (e.g., subsidence, compaction) that SETs can. The lack of differences suggests the following: (1) surface processes in the active root zone are influencing forest floor elevation more than subsurface processes, (2) subsurface processes were not large enough to effect elevation, or (3) the SETs were not installed deep enough to capture subsurface processes. CBL SEC rates did not differ significantly from SET SEC rates. The larger spatial scale of the CBL scans resulted in significantly different SEC rates from some of the plots. This was due to the CBL measuring areas missed by the SET. The greater number of points measured by CBL (~ 30,000 vs 36) increased precision and lowered standard error. The traditional SET/rSET method is currently 3–10 × cheaper than the 210Pb or CBL method, respectively, and can accurately track changes in forest floor elevation. Costs of the use of LiDAR are likely to decrease in the future with the advent of newer and more cost-effective technology. [ABSTRACT FROM AUTHOR]

Tidal marshes build elevations by below- and aboveground organic and mineral soil processes. Marsh elevation and accretion data can be used to determine if marshes are keeping pace with sea-level rise. Using a network of 54 deep rod surface elevation tables with paired feldspar marker horizon plots, we tracked elevation and accretion trends across 16 marshes in California, USA. All sites had overall positive gains across years that included severe drought conditions and extreme rain events. Marsh elevation relative to tidal datum (z*) was the key predictor for elevation and accretion rates, with higher change rates at lower z* sites. Marsh sites are clustered into three regional groups (Northern California, San Francisco Bay area, and Southern California), primarily defined by maximum temperature and annual rainfall differences. Elevation, accretion, and shallow subsidence rates were not significantly different between clusters, but their explanatory variables did vary. High-temperature days were a key predictor for elevation, accretion, and shallow subsidence rates in the state-wide analysis and San Francisco Bay regional analysis. The largest elevation gains were observed in the San Francisco Bay-Delta and some of the smallest in Humboldt Bay, with Morro Bay having the lowest accretion rate overall. Central and Southern California marshes were keeping pace or out-pacing sea-level rise, while none of the Humboldt Bay marshes were keeping pace. Marsh surface elevation data can inform management intervention and be a leading indicator for sea-level rise vulnerability. Long-term monitoring across geomorphic settings can help inform management and anticipate marsh change. [ABSTRACT FROM AUTHOR]

Australian tidal wetlands differ in important respects to better studied northern hemisphere systems, an artefact stable to falling sea levels over millennia. A network of Surface Elevation Table-Marker Horizon (SET-MH) monitoring stations has been established across the continent to assess accretionary and elevation responses to sea-level rise. This network currently consists of 289 SET-MH installations across all mainland Australian coastal states and territories. SET-MH installations are mostly in mangrove forests but also cover a range of tidal marsh and supratidal forest ecosystems. Mangroves were found to have higher rates of accretion and elevation gain than all the other categories of tidal wetland, a result attributable to their lower position within the tidal frame (promoting higher rates of accretion) higher biomass (with potentially higher rates of root growth), and lower rates of organic decomposition. While Australian tidal marshes in general show an increase in elevation over time, in 80% of locations, this was lower than the rate of sea-level rise. High rates of accretion did not translate into high rates of elevation gain, because the rate of subsidence in the shallow substrate increased with higher accretion rates (r2 = 0.87). The Australian SET-MH network, already in many locations spanning two decades of measurement, provides an important benchmark against which to assess wetland responses to accelerating sea-level rise in the decades ahead. [ABSTRACT FROM AUTHOR]

Coastal wetlands experience acute and chronic disturbances which can affect rates of surface elevation change and vertical accretion of surface sediments. Disturbance can either amplify or impair the ability of wetlands to maintain their position within the tidal frame, with implications for their long-term persistence. Using an 8-year dataset collected from coupled surface elevation table-marker horizon (SET-MH) stations spanning riverine, bayside, and barrier island settings in the Apalachicola Bay region of north Florida, USA, this study investigated decadal-scale surface elevation change and vertical accretion rates to assess wetland vulnerability to acute (Hurricane Michael) and chronic (relative sea-level rise; RSLR) disturbance in different geomorphic settings. All sites had long-term accretion rates that exceeded rates of surface elevation change (pre-Michael), indicating that surface accretion was not a good indicator of changes in surface elevation for any of these coastal geomorphic settings. Hurricane Michael increased surface elevation change rates at bayside and riverine sites; barrier island sites consistently displayed the lowest surface elevation change rates, which did not differ between pre- and post-Michael periods. Accretion rates were greatest in the riverine sites, which were characterized by highly organic soils. Barrier island and bayside sites demonstrated elevation and accretion deficits relative to the rate of RSLR for Apalachicola Bay between 2010 and 2022, indicating high vulnerability of these sites to chronic increases in sea level. These estimates of marsh resilience relied exclusively on rates of vertical change and neglecting to account for lateral erosion failed to predict that each of the three barrier island sites experienced rapid loss of the seaward SET-MH stations during the observation period. These results provide evidence of different vertical change responses among coastal wetlands of three geomorphic settings exposed to hurricanes and RSLR in the same region and suggest different timelines for long-term persistence of these sites. [ABSTRACT FROM AUTHOR]

We have investigated the evolutionary connections of the isolated neutron star (NS) populations including radio pulsars (RPs), anomalous X-ray pulsars (AXPs), soft gamma repeaters (SGRs), dim isolated NSs (XDINs), 'high-magnetic field' RPs ('HBRPs'), central compact objects (CCOs), rotating radio transients (RRATs), and long-period pulsars (LPPs) in the fallback disc model. The model can reproduce these NS families as a natural outcome of different initial conditions (initial period, disc mass, and dipole moment, μ) with a continuous μ distribution in the |$\sim 10^{27} - 5 \times 10^{30}$| G cm |$^3$| range. Results of our simulations can be summarized as follows: (1) A fraction of 'HBRPs' with relatively high μ evolve into the persistent AXP/SGR properties, and subsequently become LPPs. (2) Persistent AXP/SGRs do not have evolutionary links with CCOs, XDINs, and RRATs. (3) For a wide range of μ , most RRATs evolve passing through RP or 'HBRP' properties during their early evolutionary phases. (4) A fraction of RRATs which have the highest estimated birth rate seem to be the progenitors of XDINs. (5) LPPs, whose existence was predicted by the fallback disc model, are the sources evolving in the late stage of evolution before the discs become inactive. These results provide concrete support to the ideas proposing evolutionary connections between the NS families to account for the 'birth rate problem', the discrepancy between the cumulative birth rate estimated for these systems and the core-collapse supernova rate. [ABSTRACT FROM AUTHOR]

The Be/X-ray binary pulsar RX J0440.9+4431 went through a giant outburst in December 2022 with a peak flux of |$\sim$| 2.3 Crab in 15–50 keV. We studied the broad-band timing and spectral properties of RX J0440.9+4431 using four AstroSat observations, where the source transited between subcritical and supercritical accretion regimes. Pulsations were detected significantly above 100 keV. The pulse profiles were found to be highly luminosity- and energy-dependent. A significant evolution in the pulse profile shape near the peak of the outburst indicates a possible change in the accretion mode and beaming patterns of RX J0440.9+4431. The rms pulsed fraction was luminosity- and energy-dependent, with a concave-like feature around 20–30 keV. The depth of this feature varied with luminosity, indicating changes in the accretion column height and proportion of reflected photons. The broad-band continuum spectra were best fitted with a two-component Comptonization model with a blackbody component or a two-blackbody component model with a thermal Comptonization component. A quasi-periodic oscillation (QPO) at 60 mHz was detected at a luminosity of |$2.6 \times 10^{37}$|  erg s |$^{-1}$|⁠ , which evolved into 42 mHz at |$1.5 \times 10^{37}$|  erg s |$^{-1}$|⁠. The QPO rms were found to be energy dependent with an overall increasing trend with energy. For the first time, we found the QPO frequency varying with photon energy in an X-ray pulsar, which poses a challenge in explaining the QPO with current models such as the Keplarian and beat frequency model. Hence, more physically motivated models are required to understand the physical mechanism behind the mHz QPOs. [ABSTRACT FROM AUTHOR]

Current images of the supermassive black hole (SMBH) candidates at the centre of our Galaxy and M87 have opened an unprecedented era for studying strong gravity and the nature of relativistic sources. Very-long-baseline interferometry data show images consistent with a central SMBH within General Relativity (GR). However, it is essential to consider whether other well-motivated dark compact objects within GR could produce similar images. Recent studies have shown that dark matter (DM) haloes modelled as self-gravitating systems of neutral fermions can harbour very dense fermionic cores at their centres, which can mimic the space–time features of a black hole (BH). Such dense, horizonless DM cores can satisfy the observational constraints: they can be supermassive and compact and lack a hard surface. We investigate whether such cores can produce similar observational signatures to those of BHs when illuminated by an accretion disc. We compute images and spectra of the fermion cores with a general-relativistic ray tracing technique, assuming the radiation originates from standard |$\alpha$| discs, which are self-consistently solved within the current DM framework. Our simulated images possess a central brightness depression surrounded by a ring-like feature, resembling what is expected in the BH scenario. For Milky Way-like haloes, the central brightness depressions have diameters down to |${\sim} 35\, \mu \text{as}$| as measured from a distance of approximately |$8\,$|  kpc. Finally, we show that the DM cores do not possess photon rings, a key difference from the BH paradigm, which could help discriminate between the models. [ABSTRACT FROM AUTHOR]

The elemental abundances of stars reflect the complex enrichment history of the Galaxy. To explore and explain the metal enrichment history of the cosmic environment near our solar system, we study the evolution of 56Fe abundance over time and [Mg/Fe] versus [Fe/H] evolution in the solar neighborhood. Core-collapse supernovae make the dominant contribution in the early stages, while Type Ia supernovae (SNe Ia) have a delayed and dominant impact in the later stages. In this work, we consider the nucleosynthesis contribution of neutrino-dominated accretion flows (NDAFs) formed at the end of the lives of massive stars. The results show that the [Fe/H] gradually increases over time and eventually reaches [Fe/H] = 0 and above, reproducing the chemical enrichment process in the solar neighborhood. Before the onset of SNe Ia, the ratio of 56Fe mass to the total gas mass increases by a factor of at most ∼1.44 when NDAFs are taken into account. We find that by including NDAF in our models, the agreement with the observed metallicity distribution of metal-poor stars in the solar neighborhood (<1 kpc) is improved while not significantly altering the location of the metallicity peak. This inclusion can also reproduce the observed evolutionary change of [Mg/Fe] at [Fe/H] ∼ −1.22, bringing the ratio to match the solar abundance. Our results provide an extensive understanding of metallicity evolution in solar environments by highlighting the nucleosynthesis contribution of NDAF outflows in the solar neighborhood. [ABSTRACT FROM AUTHOR]

The rising part of a tidal disruption event light curve provides unique insight into early emission and the onset of accretion. Various mechanisms are proposed to explain the pre-peak emission, including shocks from debris interaction and reprocessing of disk emission. We study the pre-peak emission and its influence on the gas circularization by a series of gray radiation hydrodynamic simulations with varying black hole mass. We find that, given a super-Eddington fallback rate of 10 M ̇ Edd , the stream–stream collision can occur multiple times and drive strong outflows of up to 9 M ̇ Edd . By dispersing gas to ≳100 r s , the outflow can delay gas circularization and leads to sub-Eddington accretion rates during the first few stream–stream collisions. The stream–stream collision shock and circularization shock can sustain a luminosity of ∼1044 erg s−1 for days. The luminosity is generally sub-Eddington and shows a weak correlation with accretion rate at early times. The outflow is optically thick, yielding a reprocessing layer with a size of ∼1014 cm and photospheric temperature of ∼4 × 104 K. [ABSTRACT FROM AUTHOR]

This work presents the first-ever broadband (0.7–25.0 keV) timing and spectral analysis of Be-HMXB 2S 1417–624 during its 2021 outburst. Using AstroSat observations, coherent pulsations at ∼ 17.36633 s (MJD 59239.082) were detected in 0.7–7.0 keV SXT and 3.0–25.0 keV LAXPC data. The pulse profile was dual peaked at all energies, with the relative intensity of the main peak increasing with energy. The peaks in the SXT profiles were broad and comprised of several mini-structures. The LAXPC profiles were relatively smooth and had higher pulsed fractions, which increased with energy. The SXT + LAXPC simultaneous energy spectrum is well described by an absorbed power-law with exponential cut-off, a ∼ 1.6 keV black body component, and a 6.47 keV emission line. A model comprising of an absorbed power law with high energy cut-off plus a partial covering absorber and Gaussian emission line fits the spectrum quite well. These results have been compared with timing and spectral features during the previous outbursts of this transient pulsar. [ABSTRACT FROM AUTHOR]

We report a detailed spectro-temporal analysis of the black hole low mass X-ray binary 4U 1543−475 during its 2021 outburst using the data from the Large Area X-ray Proportional Counter and the Soft X-ray Telescope instruments on board AstroSat. We studied the energy and frequency dependency of the source variability to probe the origin of the disc/coronal fluctuations. Following the state transition (from soft to intermediate state), the emergence of a band-limited noise component is observed along with the power law noise when the disk is recovering from a sudden decrease in the inner disk radius. A possible correlation between the low-frequency root mean square (RMS) variability amplitude and the covering fraction of the non-thermal component is detected. During the final AstroSat observation, a flip-flop phenomenon is reported, where rapid variation in RMS occurs in concurrence with sudden flux transition. An indication of the evolution of inner disk temperature along with a significant change in thermal flux was observed during the flip-flop phase, arguing for a disk instability-driven origin for this phenomenon. Our results suggest that the long-term variability evolution is primarily affected by the coronal changes, whereas the disk behavior governs the short-term variability evolution. [ABSTRACT FROM AUTHOR]

The accreting millisecond X-ray pulsar IGR J17498−2921 went into X-ray outburst on 2023 April 13–15, for the first time since its discovery on 2011 August 11. Here, we report on the first follow-up NuSTAR observation of the source, performed on 2023 April 23, around 10 d after the peak of the outburst. The NuSTAR spectrum of the persistent emission (3–60 keV band) is well described by an absorbed blackbody with a temperature of |$kT_{\mathrm{ bb}}=1.61\pm 0.04$|  keV, most likely arising from the NS surface and a Comptonization component with power-law index |$\Gamma =1.79\pm 0.02$|⁠ , arising from a hot corona at |$kT_{e}=16\pm 2$| keV. The X-ray spectrum of the source shows robust reflection features which have not been observed before. We use a couple of self-consistent reflection models, relxill and relxillCp , to fit the reflection features. We find an upper limit to the inner disc radius of |$6\: R_{\mathrm{ ISCO}}$| and |$9\: R_{\mathrm{ ISCO}}$| from relxill and relxillCp model, respectively. The inclination of the system is estimated to be |$\simeq 40^{\circ }$| from both reflection models. Assuming magnetic truncation of the accretion disc, the upper limit of magnetic field strength at the pole of the NS is found to be |$B\lesssim 1.8\times 10^{8}$| G. Furthermore, the NuSTAR observation revealed two type-I X-ray bursts and the burst spectroscopy confirms the thermonuclear nature of the burst. The blackbody temperature reaches nearly 2.2 keV at the peak of the burst. [ABSTRACT FROM AUTHOR]