Showing papers on "X-ray binary published in 2023"
TL;DR: The population properties of compact binary mergers inferred from gravitational-wave observations of these systems during the first three LIGO-Virgo observing runs were reported in this article , where the binary black hole merger rate, allowing for evolution with redshift, was estimated to be between 17.9 and 44 Gpc−3 yr−1 at a fiducial redshift.
Abstract: We report on the population properties of compact binary mergers inferred from gravitational-wave observations of these systems during the first three LIGO-Virgo observing runs. The Gravitational-Wave Transient Catalog 3 (GWTC-3) contains signals consistent with three classes of binary mergers: binary black hole, binary neutron star, and neutron star–black hole mergers. We infer the binary neutron star merger rate to be between 10 and 1700 Gpc−3 yr−1 and the neutron star–black hole merger rate to be between 7.8 and 140 Gpc−3 yr−1, assuming a constant rate density in the comoving frame and taking the union of 90% credible intervals for methods used in this work. We infer the binary black hole merger rate, allowing for evolution with redshift, to be between 17.9 and 44 Gpc−3 yr−1 at a fiducial redshift (z=0.2). The rate of binary black hole mergers is observed to increase with redshift at a rate proportional to (1+z)κ with κ=2.9−1.8+1.7 for z≲1. Using both binary neutron star and neutron star–black hole binaries, we obtain a broad, relatively flat neutron star mass distribution extending from 1.2−0.2+0.1 to 2.0−0.3+0.3M⊙. We confidently determine that the merger rate as a function of mass sharply declines after the expected maximum neutron star mass, but cannot yet confirm or rule out the existence of a lower mass gap between neutron stars and black holes. We also find the binary black hole mass distribution has localized over- and underdensities relative to a power-law distribution, with peaks emerging at chirp masses of 8.3−0.5+0.3 and 27.9−1.8+1.9M⊙. While we continue to find that the mass distribution of a binary’s more massive component strongly decreases as a function of primary mass, we observe no evidence of a strongly suppressed merger rate above approximately 60M⊙, which would indicate the presence of a upper mass gap. Observed black hole spins are small, with half of spin magnitudes below χi≈0.25. While the majority of spins are preferentially aligned with the orbital angular momentum, we infer evidence of antialigned spins among the binary population. We observe an increase in spin magnitude for systems with more unequal-mass ratio. We also observe evidence of misalignment of spins relative to the orbital angular momentum.22 MoreReceived 4 February 2022Revised 28 October 2022Accepted 19 December 2022DOI:https://doi.org/10.1103/PhysRevX.13.011048Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasGravitational wave sourcesGravitational wavesTechniquesGravitational wave detectionGravitation, Cosmology & Astrophysics
482 citations
TL;DR: In this article , the authors report on a comprehensive analysis of simultaneous X-ray polarimetric and spectral data of the bright atoll source GX 9+9 with the IPE and NuSTAR.
Abstract: We report on a comprehensive analysis of simultaneous X-ray polarimetric and spectral data of the bright atoll source GX 9+9 with the Imaging X-ray Polarimetry Explorer (IXPE) and NuSTAR. The source is significantly polarized in the 4--8 keV band, with a degree of $2.2\% \pm 0.5\%$ (uncertainty at the 68% confidence level). The NuSTAR broad-band spectrum clearly shows an iron line, and is well described by a model including thermal disk emission, a Comptonized component, and reflection. From a spectro-polarimetric fit, we obtain an upper limit to the polarization degree of the disk of 4% (at 99% confidence level), while the contribution of Comptonized and reflected radiation cannot be conclusively separated. However, the polarization is consistent with resulting from a combination of Comptonization in a boundary or spreading layer, plus reflection off the disc, which gives a significant contribution in any realistic scenario.
25 citations
25 Apr 2023
TL;DR: In this paper , an accretion disc with an only partially ionized atmosphere flowing away from the disc at mildly relativistic velocities was proposed to explain the observed high energy-dependent X-ray polarisation in 4U 1630-47.
Abstract: Large, energy-dependent X-ray polarisation is observed in 4U 1630-47, a black hole in an X-ray binary, in the high-soft emission state. In this state, X-ray emission is believed to be dominated by a thermal, geometrically thin, optically thick accretion disc. However, the observations with the Imaging X-ray Polarimetry Explorer (IXPE) reveal an unexpectedly high polarisation degree, rising from 6% at 2 keV to 10% at 8 keV, which cannot be reconciled with standard models of thin accretion discs. We argue that an accretion disc with an only partially ionised atmosphere flowing away from the disc at mildly relativistic velocities can explain the observations.
12 citations
TL;DR: In this article , the authors used the population-level mass and spin distribution of a binary merging of one neutron star and one black hole to find the progenitors of gamma-ray bursts in the local universe.
Abstract: Compact-object binary mergers consisting of one neutron star and one black hole (NSBHs) have long been considered promising progenitors for gamma-ray bursts, whose central engine remains poorly understood. Using gravitational-wave constraints on the population-level NSBH mass and spin distributions we find that at most 20 Gpc−3 yr−1 of gamma-ray bursts in the local universe can have NSBH progenitors.
10 citations
TL;DR: In this article , the authors investigated the long-term optical variability of the Be/X-ray binary GRO J2058+42 and the possible connection with periods of enhanced X-ray activity.
Abstract: We investigate the long-term optical variability of the Be/X-ray binary GRO J2058+42 and the possible connection with periods of enhanced X-ray activity. We performed an optical spectroscopic and photometric analysis on data collected during about 18 years. We also present the first optical polarimetric observations of this source. The long-term optical light curves in the $BVRI$ bands and the evolution of the H$\alpha$ equivalent width display a sinusoidal pattern with maxima and minima that repeat every $\sim$9.5 years. The amplitude of this variability increases as the wavelength increases. The H$\alpha$ equivalent width varied from about $-0.3$ to $-15$ \AA. We found a significant decrease in the polarization degree during the low optical state. The optical maxima occur near periods of enhanced X-ray activity and are followed by a drop in the optical emission. Unlike many other Be/X-ray binaries, GRO 2058+42 does not display $V/R$ variability. The long-term optical variability agrees with the standard model of a Be/X-ray binary, where the circumstellar disk of the Be star grows and dissipates on timescales of 9--10 years. We find that the dissipation of the disk started after a major X-ray outburst. However, the stability of the H$\alpha$ line shape as a double-peak profile and the lack of asymmetries suggest the absence of a warped disk and argue against the presence of a highly distorted disk during major X-ray outbursts.
5 citations
18 Apr 2023
TL;DR: In this article , the authors classified IGR J17407-2808 as a rare K or M-type sub-subgiant or an K type main sequence star, or sub-giant star.
Abstract: IGR J17407-2808 is an enigmatic and poorly studied X-ray binary that was recently observed quasi-simultaneously with NuSTAR and XMM-Newton. In this paper we report the results of this observational campaign. During the first 60 ks of observation, the source was caught in a relatively low emission state, characterised by a modest variability and an average flux of ~8.3E-13 erg/cm^2/s (4-60 keV). Afterwards, IGR J17407-2808 entered a significantly more active emission state that persisted for the remaining ~40 ks of the NuSTAR observation. During this state, IGR J17407-2808 displayed several fast X-ray flares, featuring durations of ~1-100 s and profiles with either single or multiple peaks. The source flux in the flaring state reached values as high as 2E-9 erg/cm^2/s (4-60 keV), leading to a measured dynamic range during the NuSTAR and XMM-Newton campaign of>~ 10^3. We also analysed available archival photometric near-infrared data of IGR J17407-2808 to improve the constraints available so far on the the nature of the donor star hosted in this system. Our analysis shows that the donor star can be either a rare K or M-type sub-subgiant or an K type main sequence star, or sub-giant star. Our findings support the classification of IGR J17407-2808 as a low-mass X-ray binary. We discuss the source X-ray behaviour as recorded by NuSTAR and XMM-Newton in view of this revised classification.
5 citations
TL;DR: In this paper , the inner disk temperature and the apparent inner disk radius were found to be $0.47\pm 0.01 \rm keV and 5.33 ± 0.10 ǫ rg from the observation data modeled by the multicolor disc blackbody model.
Abstract:
MAXI J1348-630 is a low-mass X-ray black hole binary located in the Galaxy and undergone the X-ray outburst in 2019. We analyzed the observation data in very soft state during the outburst between MJD 58588 and MJD 58596 based on the Insight-HXMT observations from 2 – 20 keV via the continuum fitting method to measure the spin of the stellar-mass black hole in MAXI J1348-630. The inner disk temperature and the apparent inner disk radius were found to be $0.47\pm 0.01 \rm keV$ and 5.33 ± 0.10 Rg from the observation data modeled by the multicolor disc blackbody model. Assuming the distance of the source $D\sim 3.4 \rm kpc$, the mass of the black hole M ∼ 11 M⊙, and the inclination of the system i ∼ 29.2○, the spin is determined to be a⋆ = 0.41 ± 0.03 for fixing hardening factor at 1.6 and $n_{H}=8.6\times 10^{21} \rm cm^{-2}$. Besides, considering the uncertainty of the parameters D, M, i of this system, with the Monte Carlo analysis, we still confirm the moderate spin of the black hole as $a_{\star }=0.42^{+0.13}_{-0.50}$. Some spectral parameters (e.g., column density and hardening factor) which could affect the measurements of the BH spin are also briefly discussed.
4 citations
TL;DR: In this paper , it was shown that precession of the spin axis of the Be star can drive superorbital periods, particularly for short orbital period binaries, and with hydrodynamic simulations, the decretion disc can remain locked to the equator of the precessing Be star.
Abstract: Superorbital periods are observed in the optical light curves of many Be/X-ray binaries yet their origin has remained somewhat elusive. We suggest that precession of the spin axis of the Be star can drive superorbital periods, particularly for short orbital period binaries. We consider the short orbital period ($P_{\rm orb}=16.6\,\rm day$) and highly eccentric ($e_{\rm b}=0.72$) Be/X-ray binary A0538-66 that has a superorbital period of $421\,\rm day$. First we show that the spin axis precession timescale is about twice the observed superorbital period. Then, with hydrodynamic simulations we show that the Be star decretion disc can remain locked to the equator of the precessing Be star. At each periastron passage of the neutron star, material is accreted into a disc around the neutron star. The neutron star disc nodally precesses on the same timescale as the Be star disc and therefore both discs can contribute to the observed superorbital period. For wider and less eccentric binary systems, the Be star disc can have a larger radial extent and more complex behaviour is expected as a result of disc warping and breaking.
4 citations
1 Jan 2023
TL;DR: Low magnetic-field neutron stars in X-ray binaries are old, semi-detached binary systems containing a weakly magnetized neutron star and a low-mass companion star. They exhibit fast-time variability and produce spectacular explosions known as type-I X-ray bursts.
Abstract: In this chapter we give an overview of the properties of X-ray binary systems containing a weakly magnetized neutron star. These are old (Giga-years life-time) semi-detached binary systems containing a neutron star with a relatively weak magnetic field (less than $\sim 10^{10}$ Gauss) and a low-mass (less than $1 M_\odot$) companion star orbiting around the common center of mass in a tight system, with orbital period usually less than 1 day. The companion star usually fills its Roche lobe and transfers mass to the neutron star through an accretion disk, where most of the initial potential energy of the in-falling matter is released, reaching temperatures of tens of million Kelvin degrees, and therefore emitting most of the energy in the X-ray band. Their emission is characterized by a fast-time variability, possibly related to the short timescales in the innermost part of the system. Because of the weak magnetic field, the accretion flow can approach the neutron star until it is accreted onto its surface sometimes producing spectacular explosions known as type-I X-ray bursts. In some sources, the weak magnetic field of the neutron star ($\sim 10^8-10^9$ Gauss) is strong enough to channel the accretion flow onto the polar caps, modulating the X-ray emission and revealing the fast rotation of the neutron star at millisecond periods. These systems are important for studies of fundamental physics, and in particular for test of Relativity and alternative theories of Gravity and for studies of the equation of state of ultra-dense matter, which are among the most important goals of modern physics and astrophysics.
2 citations
TL;DR: NuSTAR and AstroSat observations of GX 9+1 reveal spectral and temporal properties of the source in the soft spectral state. The analysis yielded an inclination angle, inner disc radius, upper limits of magnetic dipole moment and magnetic field strength, and the thickness of the boundary layer. The presence of absorption edges and noise components was also observed.
Abstract: ABSTRACT We have studied the spectro-temporal properties of the neutron star low-mass X-ray binary GX 9+1 using data from NuSTAR/Focal Plane Module and AstroSat/Soft X-ray Telescope and Large Area X-ray Proportional Counter (LAXPC). The hardness–intensity diagram of the source showed it to be in the soft spectral state (banana branch) during both observations. NuSTAR spectral analysis yielded an inclination angle (θ) = 29${^{+3}_{-4}}^{\circ }$ and inner disc radius (Rin) ≤ 19 km. Assuming that the accretion disc was truncated at the Alfvén radius during the observation, the upper limits of the magnetic dipole moment (μ) and the magnetic field strength (B) at the poles of the neutron star in GX 9+1 were calculated to be 1.5 × 10 26 G cm3 and 2.1 × 10 8 G, respectively (for kA = 1). Furthermore, the thickness of the boundary layer was found to be ≃7.5 km, which yielded the radius of the neutron star to be ≤11.5 km. Flux-resolved spectral analysis with AstroSat data showed the source to be disc dominated (Fdisc/Ftotal ∼ 0.9) with a monotonic increase in mass accretion rate ($\dot{m}$) along the banana branch. The analysis also showed the presence of absorption edges at ∼1.9 and ∼2.4 keV, likely due to Si xiii and S xv, respectively. Temporal analysis with LAXPC-20 data in the 0.02–100 Hz range revealed the presence of noise components, which could be characterized by broad Lorentzian components.
2 citations
9 May 2023
TL;DR: In this paper , X-ray polarization measurements with the Imaging Xray Polarimetry Explorer 9 (IXPE) were used to probe the spin geometry of the neutron star and showed that its moment of inertia eigenvalues differ fractionally by a few parts per ten million 10 .
Abstract: Abstract In an X-ray pulsar, a neutron star accretes matter from a stellar companion through an accretion disk. The high magnetic field of the rotating neutron star disrupts the inner edge of the disc, funneling the gas to flow onto the magnetic poles on its surface. Hercules X-1 is in many ways the prototypical X-ray pulsar; it shows persistent X-ray emission and it resides with its companion HZ Her, a two-solar-mass star, at about 7~kpc from Earth 1 . Its emission varies on three distinct timescales 2 the neutron star rotates every 1.2~seconds, it is eclipsed by its companion each 1.7~days, and the system exhibits a superorbital period of 35~days which has remained remarkably stable since its discovery 3 . Several lines of evidence point to the source of this variation as the precession of the accretion disc 4,5 , the precession of the neutron star 6,7 or both 8 . Despite the many hints over the past fifty years, the precession of the neutron star itself has yet not been confirmed or refuted. We here present X-ray polarization measurements with the Imaging X-ray Polarimetry Explorer 9 (IXPE) which probe the spin geometry of the neutron star. These observations provide direct evidence that the 35-day-period is set by the free precession of the neutron star crust, which has the important implication that its moment of inertia eigenvalues differ fractionally by a few parts per ten million 10 . Furthermore, we find indications that the basic spin geometry of the neutron star is altered by torques on timescale of a few hundred days.
5 Mar 2023
TL;DR: In this paper , the authors detect a high level of polarization in the X-ray emission of the black-hole binary 4U 1630-47 in an observation with the Imaging Xray Polarimetry Explorer.
Abstract: We detect a high level of polarization in the X-ray emission of the black-hole binary 4U 1630-47 in an observation with the Imaging X-ray Polarimetry Explorer. The 2-8 keV polarization degree is 8 % at a position angle of $18^\circ$, with the polarization degree increasing significantly with energy, from ~6 % at ~2 keV to ~ 11 % at ~8 keV. The continuum emission in the spectrum of simultaneous observations with the Neutron Star Interior Composition Explorer, NICER, is well described with only a thermal disc spectrum, with stringent upper limits to any Comptonized emission from the corona. Together with the lack of significant variability in the Fourier power spectrum, this suggests that the source was in the high-soft state at the time of these observations. The NICER spectrum reveals the presence of several absorption lines in the 6-9 keV band that we fit with two ionized absorbers, providing evidence of the presence of a strong disk wind, which supports the idea that the source was in the soft state. Previous measurements of X-ray polarization in other sources in harder states were associated with the corona or the jet in those systems. Given that the corona is significantly absent in this observation of 4U 1630-47, and that the jet in black-hole binaries is quenched in the high-soft state, we speculate that in this observation of 4U 1630-47, the polarization likely arises from the direct and reflected radiation of the accretion disk in this source.
TL;DR: In this article , the authors performed a systematic, orbital-phase-dependent analysis of the reflected Fe Kα fluorescence line at 6.4 keV using over 100 NS Interior Composition Explorer observations.
Abstract: Vela X-1 is the archetypal eclipsing high-mass X-ray binary, composed of a neutron star (NS) accreting the B-star wind. It was observed by nearly all X-ray observatories, often multiple times, featuring a rich spectrum of variable emission lines. However, the precise origin of these lines in the binary system remains uncertain. We perform a systematic, orbital-phase-dependent analysis of the reflected Fe Kα fluorescence line at 6.4 keV using over 100 NS Interior Composition Explorer observations. We resolve the line variability into 500 s time bins and find that it is predominantly due to variation in the ionizing flux, with a moderate underlying phase dependence over the 9-day orbital period. Our analysis reveals a significant reflection component that cannot originate from the companion B star alone. We also find that an appreciable portion of the B-star surface is obscured opposite the eclipse, and this obscuration is not symmetric around the midpoint (phase = 0.5). We argue that an accretion stream, from the B star to the NS and distorted by the orbital motion, is responsible both for the additional fluorescence emission component and for obscuring the B star.
5 Sep 2023
TL;DR: Low-magnetic-field neutron stars in X-ray binaries are old, semi-detached binary systems containing a weakly magnetized neutron star and a low-mass companion star. They exhibit fast-time variability and produce spectacular explosions known as type-I X-ray bursts.
Abstract: We give an overview of the properties of X-ray binary systems containing a weakly magnetized neutron star. These are old (Giga-years lifetime) semi-detached binary systems containing a neutron star with a relatively weak magnetic field (less than ∼1010 Gauss) and a low-mass (less than 1 M⊙) companion star orbiting around the common center of mass in a tight system, with orbital period usually less than 1 day. The companion star usually fills its Roche lobe and transfers mass to the neutron star through an accretion disk, where most of the initial potential energy of the in-falling matter is released, reaching temperatures of tens of million Kelvin degrees, and therefore emitting most of the energy in the X-ray band. Their emission is characterized by a fast-time variability, possibly related to the short time scales in the innermost part of the system. Because of the weak magnetic field, the accretion flow can approach the neutron star until it is accreted onto its surface sometimes producing spectacular explosions known as type-I X-ray bursts. In some sources, the weak magnetic field of the neutron star (∼108–109 Gauss) is strong enough to channel the accretion flow onto the polar caps, modulating the X-ray emission and revealing the fast rotation of the neutron star at millisecond periods. These systems are important for studies of fundamental physics, and in particular for test of General Relativity and alternative theories of gravity and for studies of the equation of state of ultra-dense matter, which are among the most important goals of modern physics and astrophysics.
TL;DR: In this paper , a broadband investigation of the Z-type neutron star (NS) low mass X-ray binary (LMXB) GX 349+2 using AstroSat and NICER is reported.
Abstract:
We report a broadband investigation of the Z-type neutron star (NS) low mass X-ray binary (LMXB) GX 349+2 using AstroSat and NICER. AstroSat observed the source exhibiting large scale variability in its normal branch (NB) /flaring branch (FB) vertex and flaring branch (FB) and a moderate evolution during NICER observations. The power spectra exhibit very low-frequency noise (VLFN) and low-frequency noise (LFN)/flaring branch noise (FBN), described by a power law and an evolving Lorentzian. We investigate the energy dependence of variability components and their correlation with the spectral state to probe their origin. The joint spectra of GX 349+2 are modeled by two thermal and one non-thermal component. The source moves along the Z track, with the increasing accretion rate, further heating of the NS boundary layer, and increasing temperature/radius of the brightened hotspot at the disc-boundary layer interface/NS surface. A power law well represents the hard non-thermal coronal emission. As predicted by the gravitational redshift, we find a correlation between the line energy detected in NICER spectra and the inner disc radius with the Spearman rank correlation coefficient of 1. Using this correlation, we demonstrate the potential of a method to constrain the accreting compact object properties, including evolving continuum and line spectroscopy. We report the first detection of hard lag providing evidence of the VLFN originating from the accretion disc in NS LMXBs, representing fluctuation of propagation through the disc.
TL;DR: In this article , the authors present the results of a pilot radio-monitoring program of X1850-087 undertaken with the Karl G. Jansky Very Large Array, with simultaneous or quasi-simultaneous Swift/XRT data obtained at each epoch.
Abstract: The conditions under which accreting neutron stars launch radio-emitting jets and/or outflows are still poorly understood. The ultracompact X-ray binary X1850–087, located in the globular cluster NGC 6712, is a persistent atoll-type X-ray source that has previously shown unusual radio-continuum variability. Here we present the results of a pilot radio-monitoring program of X1850–087 undertaken with the Karl G. Jansky Very Large Array, with simultaneous or quasi-simultaneous Swift/XRT data obtained at each epoch. The binary is clearly detected in the radio in two of the six new epochs. When combined with previous data, these results suggest that X1850–087 shows radio emission at a slightly elevated hard-state X-ray luminosity of L X ≳ 2 × 1036 erg s−1, but no radio emission in its baseline hard state L X ∼ 1036 erg s−1. No clear X-ray spectral changes are associated with this factor of ≳10 radio variability. At all detected epochs, X1850–087 has a flat to inverted radio spectral index, more consistent with the partially absorbed optically thick synchrotron of a compact jet rather than the evolving optically thick to thin emission associated with transient expanding synchrotron-emitting ejecta. If the radio emission in X1850–087 is indeed due to a compact jet, then it is plausibly being launched and quenched in the hard state on timescales as short as a few days. Future radio monitoring of X1850–087 could help elucidate the conditions under which compact jets are produced around hard-state accreting neutron stars.
1 Feb 2023
TL;DR: In this paper , the initial value problem for extremal binary compact objects is analyzed with application to the study of remnant stability in binary neutron star mergers using an equation of state with quark matter.
Abstract: In this work the initial value problem for extremal binary compact objects is analyzed with application to the study of remnant stability in binary neutron star mergers. In limited respects this analysis is extended to the study of binary neutron stars using an equation of state with quark matter.
24 May 2023
TL;DR: In this paper , a broadband investigation of the Z-type neutron star (NS) low mass X-ray binary (LMXB) GX 349+2 using AstroSat and NICER is reported.
Abstract: We report a broadband investigation of the Z-type neutron star (NS) low mass X-ray binary (LMXB) GX 349+2 using AstroSat and NICER. AstroSat observed the source exhibiting large scale variability in its normal branch (NB) /flaring branch (FB) vertex and flaring branch (FB) and a moderate evolution during NICER observations. The power spectra exhibit very low-frequency noise (VLFN) and low-frequency noise (LFN)/flaring branch noise (FBN), described by a power law and an evolving Lorentzian. We investigate the energy dependence of variability components and their correlation with the spectral state to probe their origin. The joint spectra of GX 349+2 are modeled by two thermal and one non-thermal component. The source moves along the Z track, with the increasing accretion rate, further heating of the NS boundary layer, and increasing temperature/radius of the brightened hotspot at the disc-boundary layer interface/NS surface. A power law well represents the hard non-thermal coronal emission. As predicted by the gravitational redshift, we find a correlation between the line energy detected in NICER spectra and the inner disc radius with the Spearman rank correlation coefficient of 1. Using this correlation, we demonstrate the potential of a method to constrain the accreting compact object properties, including evolving continuum and line spectroscopy. We report the first detection of hard lag providing evidence of the VLFN originating from the accretion disc in NS LMXBs, representing fluctuation of propagation through the disc.
21 Feb 2023
TL;DR: In this article , the authors performed a systematic, orbital phase-dependent analysis of the reflected Fe K$\alpha$ fluorescence line at 6.4 keV using over 100 NICER observations.
Abstract: Vela X-1 is the archetypical eclipsing high-mass X-ray binary, composed of a neutron star (NS) accreting the B-star wind. It was observed by nearly all X-ray observatories, often multiple times, featuring a rich spectrum of variable emission lines. Yet, the precise origin of these lines in the binary system remains uncertain. We perform a systematic, orbital phase-dependent analysis of the reflected Fe K$\alpha$ fluorescence line at 6.4 keV using over 100 NICER observations. We resolve the line variability into 500s time bins and find that it is predominantly due to variation in the ionizing flux, with a moderate underlying phase dependence over the 9-day orbital period. Our analysis reveals a significant reflection component that cannot originate from the companion B-star alone. We also find that an appreciable portion of the B-star surface is obscured opposite the eclipse, and this obscuration is not symmetric around the mid-point (phase=0.5). We argue that an accretion stream, from the B-star to the NS and distorted by the orbital motion, is responsible for both the additional fluorescence emission component and for obscuring the B-star.
26 Apr 2023
TL;DR: In this paper , the inner disk temperature and the apparent inner disk radius were found to be $0.47\pm 0.01 \rm keV and $5.33 \rm 0.03$ for fixing hardening factor at 1.
Abstract: MAXI J1348-630 is a low-mass X-ray black hole binary located in the Galaxy and undergone the X-ray outburst in 2019. We analyzed the observation data in very soft state during the outburst between MJD 58588 and MJD 58596 based on the Insight-HXMT observations from 2 -- 20 keV via the continuum fitting method to measure the spin of the stellar-mass black hole in MAXI J1348-630. The inner disk temperature and the apparent inner disk radius were found to be $0.47\pm 0.01 \rm keV$ and $5.33\pm 0.10 \ R_{g}$ from the observation data modeled by the multicolor disc blackbody model. Assuming the distance of the source $D\sim 3.4 \rm kpc$, the mass of the black hole $M\sim 11 \ M_{\odot}$, and the inclination of the system $i\sim 29.2^{\circ}$, the spin is determined to be $a_{\star}=0.41\pm 0.03$ for fixing hardening factor at 1.6 and $n_{H}=8.6\times 10^{21} \rm cm^{-2}$. Besides, considering the uncertainty of the parameters $D, M, i$ of this system, with the Monte Carlo analysis, we still confirm the moderate spin of the black hole as $a_{\star}=0.42^{+0.13}_{-0.50}$. Some spectral parameters (e.g., column density and hardening factor) which could affect the measurements of the BH spin are also briefly discussed.
4 Jul 2023
TL;DR: In this article , the authors analyzed the K2 and TESS data taken in 2016, 2019 and 2021 of the symbiotic X-ray binaries GX 1+4 and IGR J16194-2810.
Abstract: I analyze the K2 and TESS data taken in 2016, 2019 and 2021 of the symbiotic X-ray binaries GX 1+4 and IGR J16194-2810. GX 1+4 consists of a pulsar accreting from a red giant companion in a 1160 days orbit. Since 1984, the pulsar has shown a continuous spin-down rate of $\dot{P}$=-0.1177(3) mHZ/yr. I report the detection of the spin period at an average value of 180.426(1) seconds as observed with the K2 mission and confirm that the spin period continues to increase at a rate of $\sim$1.61$\times$10$^{-7}$ s/s. The K2 and hard X-rays, as observed with Swift/BAT, varied in tandem, in agreement with other authors who proposed that the optical light arise from reprocessed X-ray emission. In the case of IGR J16194-2810, the X-ray and optical spectroscopy have been interpreted as arising from a neutron star accreting from a M2 III red giant companion. Its orbital period is unknown, while I report here the detection of a modulation with a period of 242.837 min, interpreted as the neutron star spin period. IGR J16194-2810 is thus the second symbiotic X-ray binary where the spin period is detected in optical wavelengths. This period, however, was only detected during the TESS observations of Sector 12 in 2019. The non-detection of this modulation during the observations of Sector 39 in 2021 is perhaps related with the orbital modulation, i.e. a low inclination of the orbit.
23 May 2023
TL;DR: In this article , it was shown that precession of the spin axis of the Be star can drive superorbital periods, particularly for short orbital period binaries, and with hydrodynamic simulations, the decretion disc can remain locked to the equator of the precessing Be star.
Abstract: Superorbital periods are observed in the optical light curves of many Be/X-ray binaries yet their origin has remained somewhat elusive. We suggest that precession of the spin axis of the Be star can drive superorbital periods, particularly for short orbital period binaries. We consider the short orbital period ($P_{\rm orb}=16.6\,\rm day$) and highly eccentric ($e_{\rm b}=0.72$) Be/X-ray binary A0538-66 that has a superorbital period of $421\,\rm day$. First we show that the spin axis precession timescale is about twice the observed superorbital period. Then, with hydrodynamic simulations we show that the Be star decretion disc can remain locked to the equator of the precessing Be star. At each periastron passage of the neutron star, material is accreted into a disc around the neutron star. The neutron star disc nodally precesses on the same timescale as the Be star disc and therefore both discs can contribute to the observed superorbital period. For wider and less eccentric binary systems, the Be star disc can have a larger radial extent and more complex behaviour is expected as a result of disc warping and breaking.
18 Apr 2023
TL;DR: In this paper , the authors classified IGR J17407-2808 as a rare K or M-type sub-subgiant or an K type main sequence star, or sub-giant star.
Abstract: IGR J17407-2808 is an enigmatic and poorly studied X-ray binary that was recently observed quasi-simultaneously with NuSTAR and XMM-Newton. In this paper we report the results of this observational campaign. During the first 60 ks of observation, the source was caught in a relatively low emission state, characterised by a modest variability and an average flux of ~8.3E-13 erg/cm^2/s (4-60 keV). Afterwards, IGR J17407-2808 entered a significantly more active emission state that persisted for the remaining ~40 ks of the NuSTAR observation. During this state, IGR J17407-2808 displayed several fast X-ray flares, featuring durations of ~1-100 s and profiles with either single or multiple peaks. The source flux in the flaring state reached values as high as 2E-9 erg/cm^2/s (4-60 keV), leading to a measured dynamic range during the NuSTAR and XMM-Newton campaign of >~ 10^3. We also analysed available archival photometric near-infrared data of IGR J17407-2808 to improve the constraints available so far on the the nature of the donor star hosted in this system. Our analysis shows that the donor star can be either a rare K or M-type sub-subgiant or an K type main sequence star, or sub-giant star. Our findings support the classification of IGR J17407-2808 as a low-mass X-ray binary. We discuss the source X-ray behaviour as recorded by NuSTAR and XMM-Newton in view of this revised classification.
TL;DR: In this paper , a positive relation between the spin parameter and the orbital period/orbital separation of X-ray binary (XRB) systems is found, which implies that accretion process is a common mechanism for spinning up the compact star in these diverse XRB systems.
Abstract: Abstract The origin of current angular momentum (AM) of the black hole (BH) in X-ray binary (XRB) is still unclear, which is related with the birth and/or the growth of the BH. Here we collect the spin parameters a* measured in BH XRBs and find an apparent bimodal distribution centered at ∼ 0.17 and 0.83. We find a positive relation between the spin parameter and the orbital period/orbital separation through combining distinct XRB categories, including neutron star (NS) low-mass X-ray binaries (LMXBs), Roche-lobe overflow (RLOF) BH XRBs and wind-fed BH XRBs. It seems that the AM of the compact star and the binary orbit correlates by combining the different XRB systems. These positive relations imply that accretion process is a common mechanism for spinning up the compact star in these diverse XRB systems. We infer that the low and high spin BH XRBs may experience different evolution and accretion history, which corresponds to the bimodal distribution of the BH spin parameters. The low spin BHs (a* < 0.3) are similar to the NS LMXBs, the compact star of which is spun-up by the low-level accretion, and the high spin BHs (a* > 0.5) had experienced a short hypercritical accretion ($\gg \dot{M}_\mathrm{Edd}$) period, during which, the BH spin dramatically increased.
15 May 2023
TL;DR: In this article , the authors used the evolutionary model of isolated binary evolution to reproduce the population of X-ray binaries in the nearby spiral galaxy M83 by matching model XRBs numbers/types/luminosities to observations.
Abstract: There are 214 X-ray point-sources ($L_{\rm X}>10^{35} \mathrm{erg/s}$) identified as X-ray binaries (XRBs) in the nearby spiral galaxy M83. Since XRBs are powered by accretion onto a neutron star or a black hole from a companion/donor star these systems are promising progenitors of merging double compact objects (DCOs): black hole - black hole (BH-BH), black hole - neutron star (BH-NS), or neutron star - neutron star (NS-NS) systems. The connection (i.e. XRBs evolving into DCOs) may provide some hints to the yet unanswered question: what is the origin of the LIGO/Virgo/KAGRA mergers? Available observations do not allow to determine what will be the final fate of the XRBs observed in M83. Yet, we can use evolutionary model of isolated binaries to reproduce the population of XRBs in M83 by matching model XRBs numbers/types/luminosities to observations. Knowing the detailed properties of M83 model XRBs (donor/accretor masses, their evolutionary ages and orbits) we follow their evolution to the death of donor stars to check whether any merging DCOs are formed. Although all merging DCOs in our isolated binary evolution model go through the XRB phase (defined as reaching X-ray luminosity from RLOF/wind accretion onto NS/BH above $10^{35}$ erg/s), only very few XRBs evolve to form merging (in Hubble time) DCOs. For M83 with its solar-like metallicity stars and continiuous star-formation we find that only $\sim 1-2\%$ of model XRBs evolve into merging DCOs depending on the adopted evolutionary physics. This is caused by (i) merger of donor star with compact object during common envelope phase, (ii) binary disruption at the supernova explosion of donor star, (iii) formation of a DCO on a wide orbit (merger time longer than Hubble time).
19 Jan 2023
TL;DR: In this paper , the authors investigated the long-term optical variability of the Be/X-ray binary GRO J2058+42 and the possible connection with periods of enhanced X-ray activity.
Abstract: We investigate the long-term optical variability of the Be/X-ray binary GRO J2058+42 and the possible connection with periods of enhanced X-ray activity. We performed an optical spectroscopic and photometric analysis on data collected during about 18 years. We also present the first optical polarimetric observations of this source. The long-term optical light curves in the $BVRI$ bands and the evolution of the H$\alpha$ equivalent width display a sinusoidal pattern with maxima and minima that repeat every $\sim$9.5 years. The amplitude of this variability increases as the wavelength increases. The H$\alpha$ equivalent width varied from about $-0.3$ to $-15$ \AA. We found a significant decrease in the polarization degree during the low optical state. The optical maxima occur near periods of enhanced X-ray activity and are followed by a drop in the optical emission. Unlike many other Be/X-ray binaries, GRO 2058+42 does not display $V/R$ variability. The long-term optical variability agrees with the standard model of a Be/X-ray binary, where the circumstellar disk of the Be star grows and dissipates on timescales of 9--10 years. We find that the dissipation of the disk started after a major X-ray outburst. However, the stability of the H$\alpha$ line shape as a double-peak profile and the lack of asymmetries suggest the absence of a warped disk and argue against the presence of a highly distorted disk during major X-ray outbursts.
6 Apr 2023
TL;DR: In this article , a dedicated NuSTAR observation of the neutron-star low-mass X-ray binary Z-source GX 13+1 was carried out to study the timing and spectral properties of the source.
Abstract: We analysed a dedicated NuSTAR observation of the neutron-star low-mass X-ray binary Z-source GX 13+1 to study the timing and spectral properties of the source. From the colour-colour diagram, we conclude that during that observation the source transitioned from the normal branch to the flaring branch. We fitted the spectra of the source in each branch with a model consisting of an accretion disc, a Comptonised blackbody, relativistic reflection (relxillNS), and photo-ionised absorption (warmabs). Thanks to the combination of the large effective area and good energy resolution of NuSTAR at high energies, we found evidence of relativistic reflection in both the Fe K line profile, and the Compton hump present in the 10--25 keV energy range. The inner disc radius is $R_{\rm in} \lesssim 9.6~r_g$, which allowed us to further constrain the magnetic field strength to $B \lesssim 1.8 \times 10^8$ G. We also found evidence for the presence of a hot wind leading to photo-ionised absorption of Fe and Ni, with a Ni overabundance of $\sim$6 times solar. From the spectral fits, we find that the distance between the ionising source and the slab of ionised absorbing material is $\sim 4-40 \times 10^5$ km. We also found that the width of the boundary layer extends $\sim$3 km above the surface of a neutron star, which yielded a neutron-star radius $R_{\rm NS}\lesssim 16$ km. The scenario inferred from the spectral modelling becomes self-consistent only for high electron densities in the accretion disk, $n_e \sim 10^{22}-10^{23}$ cm$^{-3}$, as expected for a Shakura-Sunyaev disc, and significantly above the densities provided by relxillNS models. These results have implications for our understanding of the physical conditions in GX 13+1.
15 Apr 2023
TL;DR: In this paper , the position angle of the X-ray emitting flow was found to be aligned with the position angles of the radio jet in the plane of the sky, indicating a misalignment between the binary axis and the black hole spin.
Abstract: Recently, the accretion geometry of the black-hole X-ray binary Cyg X-1 was probed with the X-ray polarization. The position angle of the X-ray emitting flow was found to be aligned with the position angle of the radio jet in the plane of the sky. At the same time, the observed high polarization degree could be obtained only for a high inclination of the X-ray emitting flow, indicating a misalignment between the binary axis and the black hole spin. The jet, in turn, is believed to be directed by the spin axis, hence similar misalignment is expected between the jet and binary axes. We test this hypothesis using very long (up to about 26 years) multi-band radio observations. We find the misalignment of $20^\circ$--$30^\circ$. However, on the contrary to the earlier expectations, the jet and binary viewing angles are found to be similar, while the misalignment is seen between position angles of the jet and the binary axis on the plane of the sky. Furthermore, the presence of the misalignment questions our understanding of the evolution of this binary system.
22 Feb 2023
TL;DR: In this paper , the magnetic inclination angle of a neutron star (NS) in binary systems has been investigated and its long-term evolution has been shown to depend not only on the initial parameters of the binary systems, but also on the mass transfer history and the efficiency of pulsar loss.
Abstract: The magnetic inclination angle $\chi$, namely the angle between the spin and magnetic axes of a neutron star (NS), plays a vital role in its observational characteristics. However, there are few systematic investigations on its long-term evolution, especially for accreting NSs in binary systems. Applying the model of \citet{2021MNRAS.505.1775B} and the binary evolution code \mesa{}, we simultaneously simulate the evolution of the accretion rate, spin period, magnetic field, and magnetic inclination angle of accreting NSs in intermediate/low X-ray binaries (I/LMXBs). We show that the evolution of $\chi$ depends not only on the initial parameters of the binary systems, but also on the mass transfer history and the efficiency of pulsar loss. Based on the calculated results we present the characteristic distribution of $\chi$ for various types of systems including ultracompact X-ray binaries, binary millisecond pulsars, and ultraluminous X-ray sources, and discuss their possible observational implications.