X-ray Binaries Research Articles

Galactic runaway O and Be stars found usingGaiaDR3

Context.A relevant fraction of massive stars are runaway stars. These stars move with a significant peculiar velocity with respect to their environment.Aims.We aim to discover and characterize the population of massive and early-type runaway stars in the GOSC and BeSS catalogs usingGaiaDR3 astrometric data.Methods.We present a two-dimensional method in the velocity space to discover runaway stars as those that deviate significantly from the velocity distribution of field stars. Field stars are considered to follow the Galactic rotation curve.Results.We found 106 O runaway stars, 42 of which were not previously identified as runaways. We found 69 Be runaway stars, 47 of which were not previously identified as runaways. The dispersion of runaway stars is a few times higher inZandbthan that of field stars. This is explained by the ejections they underwent when they became runaways. The percentage of runaways is 25.4% for O-type stars, and it is 5.2% for Be-type stars. In addition, we conducted simulations in three dimensions for our catalogs. They revealed that these percentages could increase to ∼30% and ∼6.7%, respectively. Our runaway stars include seven X-ray binaries and one gamma-ray binary. Moreover, we obtain velocity dispersions of ∼5 km s−1perpendicular to the Galactic plane for O- and Be-type field stars. These values increase in the Galactic plane to ∼7 km s−1for O-type stars due to uncertainties and to ∼9 km s−1for Be-type stars due to Galactic velocity diffusion.Conclusions.The excellentGaiaDR3 astrometric data have allowed us to identify a significant number of O-type and Be-type runaways in the GOSC and BeSS catalogs. The higher percentages and higher velocities found for O-type compared to Be-type runaways underline that the dynamical ejection scenario is more likely than the binary supernova scenario. Our results open the door to identifying new high-energy systems among our runaways by conducting detailed studies.

Constraints on the rotating self-dual black hole with quasi-periodic oscillations

An impressive feature of loop quantum gravity (LQG) is that it can elegantly resolve both the big bang and black hole singularities. By using the Newman-Janis algorithm, a regular and effective rotating self-dual black hole (SDBH) metric could be constructed, which alters the Kerr geometry with a polymeric function P from the quantum effects of LQG geometry. In this paper, we investigate its impact on the frequency characteristics of the X-ray quasi-periodic oscillations (QPOs) from 5 X-ray binaries and contrast it with the existing results of the orbital, periastron precession and nodal precession frequencies within the relativistic precession model. We apply a Monte Carlo Markov Chain (MCMC) simulation to examine the possible LQG effects on the X-ray QPOs. We found that the best constraint result for the rotating self-dual geometry from LQG came from the QPOs of X-ray binary GRO J1655-40, which establish an upper bound on the polymeric function P less than 6.15 × 10-3 at 95% confidence level. This bound leads to a restriction on the polymeric parameter δ of LQG to be 0.66.

A Phase-resolved View of the Low-frequency Quasiperiodic Oscillations from the Black Hole Binary MAXI J1820+070

Although low-frequency quasiperiodic oscillations (LFQPOs) are commonly detected in the X-ray light curves of accreting black hole X-ray binaries, their origin still remains elusive. In this study, we conduct phase-resolved spectroscopy in a broad energy band for LFQPOs in MAXI J1820+070 during its 2018 outburst, utilizing Insight-HXMT observations. By employing the Hilbert–Huang transform method, we extract the intrinsic quasiperiodic oscillation (QPO) variability, and obtain the corresponding instantaneous amplitude, phase, and frequency functions for each data point. With well-defined phases, we construct QPO waveforms and phase-resolved spectra. By comparing the phase-folded waveform with that obtained from the Fourier method, we find that phase folding on the phase of the QPO fundamental frequency leads to a slight reduction in the contribution of the harmonic component. This suggests that the phase difference between QPO harmonics exhibits time variability. Phase-resolved spectral analysis reveals strong concurrent modulations of the spectral index and flux across the bright hard state. The modulation of the spectral index could potentially be explained by both the corona and jet precession models, with the latter requiring efficient acceleration within the jet. Furthermore, significant modulations in the reflection fraction are detected exclusively during the later stages of the bright hard state. These findings provide support for the geometric origin of LFQPOs and offer valuable insights into the evolution of the accretion geometry during the outburst in MAXI J1820+070.

Evolution of the X-ray Binary System Sco X-1

Evolution of the X-ray Binary System Sco X-1

A quantitative explanation of the radio – X-ray correlation in black-hole X-ray binaries

Context. The observed correlation between the radio and X-ray fluxes in the hard state of black-hole X-ray binaries (BHXRBs) has been in existence for over two decades. It is currently accepted that the hard X-rays in BHXRBs come from Comptonization in the corona and the radio emission from the relativistic jet (Lorentz γ ≫ 1), which is a narrow structure of a few Rg = GM/c2 at its base. The jet and the corona, however, are separate entities with hardly any communication between them, apart from the fact that both are fed from the accreting matter. Aims. It is also widely accepted that the accretion flow around the black holes in BHXRBs consists of a thin outer disk and a hot inner flow. From this hot inner flow, which has a positive Bernoulli integral, an outflow must emanate in the hard and hard-intermediate states of the source. By considering Compton up-scattering of soft disk photons in the outflow (i.e., in the outflowing “corona”, which is a wider structure of tens to hundreds of Rg at its base) as the mechanism that produces the hard X-ray spectrum, we have been able to quantitatively explain a number of observed correlations. Here, we investigate whether this outflowing corona can also explain the observed radio – X-ray correlation. We remark that the outflowing corona (wide, with a low Lorentz γ) is completely separate from the relativistic jet (narrow, with a high Lorentz γ). The two may coexist, with the jet at the rotation axis and the corona around it. Methods. We considered parabolic outflow models, which we have successfully used in the explanation of other correlations regarding GX 339-4 in the hard and hard-intermediate states, and computed the radio emission at 8.6 GHz coming from them, as well as the power-law photon-number spectral index Γ of the Comptonized hard X-rays produced in them. Thus, we have a correlation between the computed radio flux FR at 8.6 GHz and the computed spectral index Γ of the hard X-ray spectrum. This correlation is a theoretical prediction, since both FR and Γ are computed from the model and, to our knowledge, no such correlation has been constructed from observations. This prediction can be confirmed or proven wrong in future outbursts of GX 339-4. Based upon observations, we also produced a correlation between the observed hard X-ray flux FX and the observed index Γ. Thus, for each value of Γ, observed or computed, we have the corresponding values of the observed FX and the computed FR, which we plotted against each other. Results. For GX 339-4, we found that our model calculations for FR and Γ, with Γ as the link between the observed FX and the computed FR, successfully reproduce the observed correlation of FR ∝ FX0.6 in the hard state. In addition, in the hard-intermediate state of GX 339-4, this correlation breaks down and we predict that, in future outbursts of the source, the FR will exhibit first a sudden increase and then a sharp drop within a very narrow range of values of FX. Such a sharp drop of the FR has been observed in other sources. Conclusions. In our picture both the radio and the hard X-ray emission come from the same region, namely the outflow, and it is therefore not surprising that they are correlated. Since in a parabolic outflow with constant outflow speed the density is largest at its bottom, the soft photons, coming from below, see something appearing similar to a “slab”, with a moderate optical depth (up to ten in the hard state) along the outflow and an order of magnitude larger in the perpendicular direction. We remark that it is a slab geometry that is invoked to explain the observed X-ray polarization from BHXRBs. Because of this, we predict that the X-ray polarization of GX 339-4 will be parallel to the outflow in the hard state and perpendicular to it in the hard-intermediate state.

Magnetic support, wind-driven accretion, coronal heating, and fast outflows in a thin magnetically arrested disc

ABSTRACT Accretion discs properties should deviate from standard theory when magnetic pressure exceeds the thermal pressure. To quantify these deviations, we present a systematic study of the dynamical properties of magnetically arrested discs (MADs), the most magnetized type of accretion disc. Using an artificial cooling function to regulate the gas temperature, we study MADs of three different thermal thicknesses, hth/r = 0.3, 0.1, and 0.03. We find that the radial structure of the disc is never mostly supported by the magnetic field. In fact, thin MADs are very near Keplerian. However, as discs gets colder, they become more magnetized and the largest deviations from standard theory appear in our thinnest disc with hth/r = 0.03. In this case, the disc is much more extended vertically and much less dense than in standard theory because of vertical support from the turbulent magnetic pressure and wind-driven angular momentum transport that enhances the inflow speed. The thin disc also dissipates a lot of thermal energy outside of z/r = ±0.03 and a significant fraction of this dissipation happens in mildly relativistic winds. The enhanced dissipation in low-density regions could possibly feed coronae in X-ray binaries (XRBs) and active galactic nuclei (AGNs). Wind-driven accretion will also impact the dynamical evolution of accretion discs and could provide a mechanism to explain the rapid evolution of changing-look AGN and the secular evolution of XRBs. Finally, our MAD winds have terminal velocities and mass-loss rates in good agreement with the properties of ultrafast outflows observed in AGN.

Simultaneous NICER and NuSTAR Observations of the Ultracompact X-Ray Binary 4U 0614+091

We present the first joint NuSTAR and NICER observations of the ultracompact X-ray binary 4U 0614+091. This source shows quasiperiodic flux variations on the timescale of ∼days. We use reflection modeling techniques to study various components of the accretion system as the flux varies. We find that the flux of the reflected emission and the thermal components representing the disk and the compact object trend closely with the overall flux. However, the flux of the power-law component representing the illuminating X-ray corona scales in the opposite direction, increasing as the total flux decreases. During the lowest flux observation, we see evidence of accretion disk truncation from roughly 6 gravitational radii to 11.5 gravitational radii. This is potentially analogous to the truncation seen in black hole low-mass X-ray binaries, which tends to occur during the low/hard state at sufficiently low Eddington ratios.

Accretion flows in the hard state of black hole X-ray binaries: the effect of hot gas condensation

ABSTRACT It is commonly believed that accretion discs are truncated and their inner regions are described by advection dominated accretion flows (ADAFs) in the hard spectral state of black hole X-ray binaries. However, the increasing occurrence of a relativistically blurred Fe K α line together with a hard continuum points to the existence of a thin disc located near the innermost stable circular orbit (ISCO). Assuming the accretion in the hard state is via an ADAF extending to near 100 Schwarzschild radii, which is supplied by either a stellar wind from a companion star or resulting from an evaporated disc, we study the possible condensation of the hot gas during its accretion towards the black hole. It is found that a small fraction of the ADAF condenses into a cold disc as a consequence of efficient radiative cooling at small distances, forming a disc-corona configuration near the ISCO. This takes place for low accretion rates corresponding to luminosities ranging from ∼10−3 to a few per cent of the Eddington luminosity. The coexistence of the weak inner disc and the dominant hot accretion flow provides a natural explanation of the broad K α line in the hard state. Detailed computations demonstrate that such accretion flows produce a hard X-ray spectrum accompanied by a weak disc component with a negative correlation between the 2 and 10 keV photon index and the Eddington ratio. The predicted spectrum of Cygnus X-1 and the correlation between the photon index and the Eddington ratio are in good agreement with observations.

Sulphur X-ray absorption in the local ISM

ABSTRACT We present a study S K-edge using high-resolution HETGS Chandra spectra of 36 low-mass X-ray binaries. For each source, we have estimated column densities for S i, S ii, S iii, S xiv, S xv, and S xvi ionic species, which trace the neutral, warm, and hot phases of the Galactic interstellar medium. We also estimated column densities for a sample of interstellar dust analogues. We measured their distribution as a function of Galactic latitude, longitude, and distances to the sources. While the cold-warm column densities tend to decrease with the Galactic latitude, we found no correlation with distances or Galactic longitude. This is the first detailed analysis of the sulphur K-edge absorption due to ISM using high-resolution X-ray spectra.

An empirical connection between line-emitting regions and X-rays heating the accretion disc in BH-LMXB MAXI J1820+070

ABSTRACT The recurring transient outbursts in low-mass X-ray binaries (LMXBs) provide ideal laboratories to study the accretion process. Unlike their supermassive relatives, LMXBs are far too small and distant to be imaged directly. Fortunately, phase-resolved spectroscopy can provide an alternative diagnostic to study their highly complex, time-dependent accretion discs. The primary spectral signature of LMXBs are strong, disc-formed emission lines detected at optical wavelengths. The shape, profile, and appearance/disappearance of these lines change throughout a binary orbit, and thus, can be used to trace how matter in these discs behaves and evolves over time. By combining a Swift multiwavelength monitoring campaign, phase-resolved spectroscopy from the Gran Telescopio Canarias (GTC) and Liverpool Telescope, and modern astrotomography techniques, we find a clear empirical connection between the line emitting regions and physical properties of the X-rays heating the disc in the black hole LMXB MAXI J1820+070 during its 2018 outburst. In this paper, we show how these empirical correlations can be used as an effective observational tool for understanding the geometry and structure of a LMXB accretion disc and present further evidence for an irradiation-driven warped accretion disc present in this system.

New transient ULX candidate in NGC 4254: evidence of circumbinary disc?

ABSTRACT This paper presents the identification of a new transient ultraluminous X-ray source (ULX) candidate (ULX-3) with reaching a peak luminosity of ∼4 × 1039 erg s−1 in NGC 4254 by using archival Chandra, Swift/X-Ray Telescope, Hubble Space Telescope, and JWST observations. From precise astrometric calculations, unique optical, near-infrared, and mid-infrared counterparts were found. The spectral energy distribution (SED) and colour–magnitude diagrams of counterparts of the new ULX candidate were plotted to constrain the nature of the possible donor star. Evidence of a circumbinary disc was found from its SED with two blackbody temperatures of 1000 and 200 K. Moreover, according to the X-ray hardness ratios, ULX-3 exhibits very hard to very soft transitions as seen in some high-mass X-ray binaries with Be-star donors. Moreover, ULX-3 varies by more than two orders of magnitude in the 0.3–10 keV energy band as seen in typical transient ULXs.

Dataset of Classified Chandra Sources in Globular Clusters

We present a collection of classified X-ray sources in Globular Clusters (GCs) observed by the Chandra X-ray Observatory, including active binaries, cataclysmic variables, millisecond pulsars, and low-mass X-ray binaries. We cross-match the most accurate published positions from multiwavelength observations of these sources to the Chandra Source Catalog Release 2.1, and the HST UV Globular Cluster Survey to extract their multiwavelength properties. The data set can be accessed via an interactive website (https://home.gwu.edu/~kargaltsev/XCLASS_GC) and used as a training data set for machine-learning classification of unidentified X-ray sources in GCs.

X-ray luminosity-star formation rate scaling relation: Constraints from the eROSITA Final Equatorial Depth Survey (eFEDS)

Aims.We present measurements of the relation between X-ray luminosity and star formation activity for a sample of normal galaxies spanning the redshift range between 0 and 0.25. We use data acquired by SRG/eROSITA for the performance and verification phase program called eROSITA Final Equatorial Depth Survey (eFEDS). The eFEDS galaxies are observed in the 0.2−2.3 keV band.Methods.Making use of a wide range of ancillary data, spanning from the ultraviolet (UV) to mid-infrared wavelengths (MIR), we estimated the star formation rate (SFR) and stellar mass (Mstar) of 888 galaxies, using Code Investigating GALaxy Emission (CIGALE). In order to study sources whose X-ray emission is dominated by X-ray binaries (XRBs), we classified these galaxies into normal galaxies and active galactic nuclei by making use of the observed fluxes in the X-ray, optical, and MIR ranges, as well as the results from the SED fitting. To isolate the contribution of XRBs, which scale with the SFR andMstar, we subtracted the contribution of hot gas, coronally active binaries, and cataclysmic variables to the total X-ray emission. We divided our sample of normal galaxies in star-forming (SFGs) and quiescent galaxies according to their position on the main sequence.Results.We confirm a linear correlation between the X-ray luminosity and the SFR for our sample of SFGs, shown previously in the literature. However, we find this relation to be strongly biased by the completeness limit of the eFEDS survey. Correcting for completeness, we find the fitted relation to be consistent with the literature. We also investigated the relation between X-ray emission from both LMXBs and HMXBs populations withMstarand SFR, respectively. Correcting for completeness, we find our fitted relation to considerably scatter from the literature relation at high specific SFR (SFR/Mstar). We conclude that without accounting for X-ray non-detections, it is not possible to employ eFEDS data to study the redshift evolution of the LMXBs and HMXBs contributions due to completeness issues. Furthermore, we find our sources to largely scatter from the expected Lx/SFR vs. specific SFR relation at high redshift. We discuss the dependence of the scatter on the stellar mass, metallicity, or the globular cluster content of the galaxy.

О критериях реализации магнитосферной аккреции в рентгеновских двойных системах

We consider the accretion process in the X-ray binary systems with neutron stars as relativistic components. We focus our investigation at the question of magnetospheres formation in the process of mass accretion onto the neutron stars in these systems. We note that the answer to this question depends, in particular, on the geometry and physical parameters of the accretion flow. We show that magnetospheres are the most likely to form in the systems with spherical (quasi-spherical) accretion. Formation of a magnetosphere is less likely in the case of accretion through the Keplerian disk or in the MAD-accretion scenario. This findings should be taken into account in the estimation of expected number of accreting X-ray pulsars in the low-mass X-ray binaries.

Can Cosmologically Coupled Mass Growth of Black Holes Solve the Mass Gap Problem?

Observations of elliptical galaxies suggest that black holes (BHs) might serve as dark energy candidates, coupled to the expansion of the Universe. According to this hypothesis, the mass of a BH could increase as the Universe expands. BH low-mass X-ray binaries (LMXBs) in the Galactic disk were born several gigayears ago, making the coupling effect potentially significant. In this work, we calculate the evolution of BH binaries with a binary population synthesis method to examine the possible influence of cosmologically coupled growth of BHs, if it really exists. The measured masses of the compact objects in LMXBs show a gap around ∼2.5–5 M ⊙, separating the most-massive neutron stars from the least-massive BHs. Our calculated results indicate that considering the mass growth seems to (partially) account for the mass gap and the formation of compact BH LMXBs, alleviating the challenges in modeling the formation and evolution of BH LMXBs with traditional theory. However, critical observational evidence like the detection of intermediate-mass BH binaries is required to test this hypothesis.

Black Holes in Globular Clusters

Black holes are the laboratory for extreme physics research in the universe, and the detection of black holes is one of the most cutting-edge international scientific goals at present. Globular clusters are old, self-gravity-bound object systems in the Milky Way that contain millions of stars with a high stellar densities inside. Hundreds of pulsar objects have been observed in globular clusters, but the existence of black holes in globular clusters remains an unsolved mystery. A globular cluster may have an intermediatemass black hole at its centre, with masses ranging from 1, 000 to 10, 000 times solar masses. At the same time, there may be a large number of stellar black holes in globular clusters, which will affect the evolution of globular clusters and form. some special objects in globular clusters, which can be observed and confirmed by astronomical observation equipment. This paper will focus on the possible observational features of the presence of black holes in globular clusters and their effects on the properties of globular clusters. Black holes are coupled with their host globular clusters through dynamics, which are important sites for the formation of black hole X-ray binaries and gravitational wave sources, and black holes change the dynamical structure and evolutionary processes of their host clusters. Therefore, searching for X-ray sources, detecting gravitational wave signals, and studying the characteristics of globular clusters are important astronomical evidence for detecting black holes in globular clusters.

Ultraluminous X-ray sources are beamed

ABSTRACT We show that magnetar models for ultraluminous X-ray sources (ULXs) have serious internal inconsistencies. The magnetic fields required to increase the limiting luminosity for radiation pressure above the observed (assumed isotropic) luminosities are completely incompatible with the spin-up rates observed for pulsing ULXs. We note that at least one normal Be-star + neutron star system, with a standard (non-magnetar) field, is observed to become a ULX during a large outburst and return to its previous Be-star binary state afterwards. We note further that recent polarimetric observations of the well-studied binary Cyg X-3 reveal that it produces strong emission directed away from the observer, in line with theoretical predictions of its total accretion luminosity from evolutionary arguments. We conclude that the most likely explanation for ULX behaviour involves radiation beaming by accretion disc winds. A large fraction of X-ray binaries must pass through a ULX state in the course of their evolution.

AstroSat View of the Neutron Star Low-mass X-Ray Binary GX 340+0

Understanding the spectral evolution along the “Z”-shaped track in the hardness–intensity diagram of Z sources, which are a class of luminous neutron star low-mass X-ray binaries, is crucial to probe accretion processes close to the neutron star. Here, we study the horizontal branch (HB) and the normal branch (NB) of the Z source GX 340+0 using AstroSat data. We find that the HB and the NB appear as two different types of X-ray intensity dips, which can appear in any sequence and with various depths. Our 0.8–25 keV spectra of dips and the hard apex can be modeled by the emissions from an accretion disk, a Comptonizing corona covering the inner disk, and the neutron star surface. We find that as the source moves onto the HB, the corona is replenished and energized by the disk and a reduced amount of disk matter reaches the neutron star surface. We also conclude that quasiperiodic oscillations during HB/NB are strongly associated with the corona and explain the evolution of strength and hard lag of this timing feature using the estimated coronal optical depth evolution.

Exploring the correlation between Hα-to-UV ratio and burstiness for typical star-forming galaxies at z ∼ 2

ABSTRACT The $\rm {H}\alpha$-to-UV luminosity ratio ($L(\text{H}\alpha)/L(\rm UV)$) is often used to probe bursty star formation histories (SFHs) of star-forming galaxies and it is important to validate it against other proxies for burstiness. To address this issue, we present a statistical analysis of the resolved distribution of star formation rate surface density (ΣSFR) as well as stellar age and their correlations with the globally measured $L(\text{H}\alpha)/L(\rm UV)$ for a sample of 310 star-forming galaxies in two redshift bins of 1.37 < z < 1.70 and 2.09 < z < 2.61 observed by the MOSFIRE Deep Evolution Field (MOSDEF) survey. We use the multiwaveband CANDELS/3D-HST imaging of MOSDEF galaxies to construct ΣSFR and stellar age maps. We analyse the composite rest-frame far-ultraviolet spectra of a subsample of MOSFIRE Deep Evolution Field (MOSDEF) targets obtained by the Keck Low Resolution Imager and Spectrometer (LRIS), which includes 124 star-forming galaxies (MOSDEF-LRIS) at redshifts 1.4 < z < 2.6, to examine the average stellar population properties, and the strength of age-sensitive far-ultraviolet spectral features in bins of $L(\text{H}\alpha)/L(\rm UV)$. Our results show no significant evidence that individual galaxies with higher $L(\text{H}\alpha)/L(\rm UV)$ are undergoing a burst of star formation based on the resolved distribution of ΣSFR of individual star-forming galaxies. We segregate the sample into subsets with low and high $L(\text{H}\alpha)/L(\rm UV)$. The high-$L(\text{H}\alpha)/L(\rm UV)$ subset exhibits, on average, an age of $\log [\rm {Age/yr}]$ = 8.0, compared to $\log [\rm {Age/yr}]$ = 8.4 for the low-$L(\text{H}\alpha)/L(\rm UV)$ galaxies, though the difference in age is significant at only the 2σ level. Furthermore, we find no variation in the strengths of Si iv λλ1393, 1402 and C iv λλ1548, 1550 P-Cygni features from massive stars between the two subsamples, suggesting that the high-$L(\text{H}\alpha)/L(\rm UV)$ galaxies are not preferentially undergoing a burst compared to galaxies with lower $L(\text{H}\alpha)/L(\rm UV)$. On the other hand, we find that the high-$L(\text{H}\alpha)/L(\rm UV)$ galaxies exhibit, on average, more intense He ii λ1640 emission, which may possibly suggest the presence of a higher abundance of high-mass X-ray binaries.

Numerical simulations of relativistic jets

In this paper, we review recent and ongoing work by our group on numerical simulations of relativistic jets. Relativistic outflows in astrophysics are related to dilute, high energy plasmas, with physical conditions out of the reach of current laboratory capabilities. Simulations are thus imperative for the study of these objects. We present a number of such scenarios that have been studied by our group at the Universitat de València. In particular, we have focused on the evolution of extragalactic outflows through galactic and intergalactic environments, deceleration by interaction with stars or clouds or the propagation of jets in X-ray binaries and interaction with stellar winds from massive companions. All also share their role as particle acceleration sites and production of non-thermal radiation throughout the electromagnetic spectrum. Therefore, our work is not only aimed at understanding the impact of outflows on their environments and thus their role in galaxy and cluster evolution, but also the nature and capabilities of these sites as generators of high- and very-high-energy radiation and cosmic rays.