arXiv subjects

Yong Shao

Publications and source records attributed to Yong Shao.

At least 37 records · Page 2Linked to original sources

arXiv2024

Constraining Mass Transfer Models with Galactic Neutron Star$-$White Dwarf Binaries as Gravitational Wave Sources

Neutron star$-$white dwarf (NSWD) binaries are one of the most abundant sources of gravitational waves (GW) in the Milky Way. These GW sources are the evolutionary products of primordial binaries that experienced many processes of binary interaction. We employ a binary population synthesis method to investigate the properties of Galactic NSWD binaries detectable by the Laser Interferometer Space Antenna (LISA). In this paper, only the NSWD systems with a COWD or ONeWD component are included. We consider various models related to mass transfer efficiencies during primordial binary evolution, supernova explosion mechanisms at NS formation, common envelope ejection efficiencies, and critical WD masses that determining the stability of mass transfer between WDs and NSs. Based on our calculations, we estimate that tens to hundreds of LISA NSWD binaries exist in the Milky Way. We find that the detection of LISA NSWD binaries is able to provide profound insights into mass transfer efficiencies during the evolution of primordial binaries and critical WD masses during mass transfer from a WD to an NS.

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arXiv2024

On the Formation of Double Neutron Stars in the Milky Way: Influence of Key Parameters

The detection of gravitational wave events has stimulated theoretical modeling of the formation and evolution of double compact objects (DCOs). However, even for the most studied isolated binary evolution channel, there exist large uncertainties in the input parameters and treatments of the binary evolution process. So far, double neutron stars (DNSs) are the only DCOs for which direct observations are available through traditional electromagnetic astronomy. In this work, we adopt a population synthesis method to investigate the formation and evolution of Galactic DNSs. We construct 324 models for the formation of Galactic DNSs, taking into account various possible combinations of critical input parameters and processes such as mass transfer efficiency, supernova type, common envelope efficiency, neutron star kick velocity, and pulsar selection effect. We employ Bayesian analysis to evaluate the adopted models by comparing with observations. We also compare the expected DNS merger rate in the Galaxy with that inferred from the known Galactic population of Pulsar-NS systems. Based on these analyses we derive favorable range of the aforementioned key parameters.

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arXiv2023

The Nearest Neutron Star Candidate in a Binary Revealed by Optical Time-domain Surveys

The near-Earth (within $\sim 100$ pc) supernova explosions in the past several million years can cause the global deposition of radioactive elements (e.g., $^{60}$Fe) on Earth. The remnants of such supernovae are too old to be easily identified. It is therefore of great interest to search for million-year-old near-Earth neutron stars or black holes, the products of supernovae. However, neutron stars and black holes are challenging to find even in our Solar neighbourhood if they are not radio pulsars or X-ray/$γ$-ray emitters. Here we report the discovery of one of the nearest ($127.7 \pm 0.3$ pc) neutron star candidates in a detached single-lined spectroscopic binary LAMOST J235456.73+335625.9 (hereafter J2354). Utilizing the time-resolved ground-based spectroscopy and space photometry, we find that J2354 hosts an unseen compact object with $M_{\mathrm{inv}}$ being $1.4 \sim 1.6\ M_{\odot}$. The follow-up Swift ultraviolet (UV) and X-ray observations suggest that the UV and X-ray emission is produced by the visible star rather than the compact object. Hence, J2354 probably harbours a neutron star rather than a hot ultramassive white dwarf. Two-hour exceptionally sensitive radio follow-up observations with Five-hundred-meter Aperture Spherical radio Telescope fail to reveal any pulsating radio signals at the $6σ$ flux upper limit of $12.5\ μ\mathrm{Jy}$. Therefore, the neutron star candidate in J2354 can only be revealed via our time-resolved observations. Interestingly, the distance between J2354 and our Earth can be as close as $\sim 50$ pc around $2.5$ Myrs ago, as revealed by the Gaia kinematics. Our discovery demonstrates a promising way to unveil the hidden near-Earth neutron stars in binaries by exploring the optical time domain, thereby facilitating understanding of the metal-enrichment history in our Solar neighbourhood.

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arXiv2023

Detection Prospects of Fast-merging Gravitational Wave Sources in M31

It is widely accepted that quite a number of double compact objects (DCOs) in the Milky Way can be identified by future space-based gravitational wave (GW) detectors, while systematic investigations on the detection of the GW sources in nearby galaxies are still lacking. In this paper, we present calculations of potential populations of GW sources for all types of DCOs in the Local Group galaxy M31. For M31, we use an age-dependent model for the evolution of the metallicity and the star-formation rate. By varying assumptions of common-envelope ejection efficiencies and supernova-explosion mechanisms during binary evolution, we make predictions on the properties of DCOs that can be detected by the Laser Interferometer Space Antenna (LISA). Our calculations indicate that a few (a dozen) DCOs are likely to be observed by LISA during its 4 (10) yr mission. We expect that the sources with black-hole components are more likely to be firstly identified during a 4-yr mission since these binaries have relatively large chirp masses, while the systems with white-dwarf components dominate the overall population of detectable GW sources during a 10-yr mission. LISA can only detect very tight fast-merging systems in M31, corresponding to the peak of orbital period distribution from $\sim 2$ min for double white dwarfs to $\sim 20$~min for double black holes.

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arXiv2023

Multi-messenger observations of double neutron stars in Galactic disk with gravitational and radio waves

We evaluate the prospects for radio follow-up of the double neutron stars (DNSs) in the Galactic disk that could be detected through future space-borne gravitational wave (GW) detectors. We first simulate the DNS population in the Galactic disk that is accessible to space-borne GW detectors according to the merger rate from recent LIGO results. Using the inspiraling waveform for the eccentric binary, the average number of the DNSs detectable by TianQin (TQ), LISA, and TQ+LISA are 217, 368, and 429, respectively. For the joint GW detection of TQ+LISA, the forecasted parameter estimation accuracies, based on the Fisher information matrix, for the detectable sources can reach the levels of $ΔP_{\mathrm b}/P_{\mathrm b} \lesssim 10^{-6}$, $ΔΩ\lesssim 100~{\mathrm {deg}}^2$, $Δe/e \lesssim 0.3$, and $Δ\dot{P}_{\mathrm b} / \dot{P}_{\mathrm b} \lesssim 0.02$. These estimation accuracies are fitted in the form of power-law function of signal-to-noise ratio. Next, we simulate the radio pulse emission from the possible pulsars in these DNSs according to pulsar beam geometry and the empirical distributions of spin period and luminosity. For the DNSs detectable by TQ+LISA, the average number of DNSs detectable by the follow-up pulsar searches using the Parkes, FAST, SKA1, and SKA are 8, 10, 43, and 87, respectively. Depending on the radio telescope, the average distances of these GW-detectable pulsar binaries vary from 1 to 7 kpc. Considering the dominant radiometer noise and phase jitter noise, the timing accuracy of these GW-detectable pulsars can be as low as 70 ${\rm ns}$ while the most probable value is about 100 $μ{\rm s}$.

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arXiv2022

On the Neutron Star/Black Hole Mass Gap and Black Hole Searches

Mass distribution of black holes in low-mass X-ray binaries previously suggested the existence of a $ \sim 2-5M_{\odot} $ mass gap between the most massive neutron stars and the least massive black holes, while some recent evidence appears to support that this mass gap is being populated. Whether there is a mass gap or not can potentially shed light on the physics of supernova explosions that form neutron stars and black holes, although significant mass accretion of neutron stars including binary mergers may lead to the formation of mass-gap objects. In this review, I collect the compact objects that are probable black holes with masses being in the gap. Most of them are in binaries, their mass measurements are obviously subject to some uncertainties. Current observations are still unable to confidently infer an absence or presence of the mass gap. Ongoing and future surveys are expected to build the mass spectrum of black holes which can be used to constrain the process of their formation especially in binaries. I describe the theoretical predictions for the formation of black holes in various types of binaries, and present some prospects of searching for black holes via electromagnetic and gravitational wave observations.

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arXiv2022

A long-period pre-ELM system discovered from LAMOST medium-resolution survey

We present LAMOST~J041920.07+072545.4 (hereafter J0419), a close binary consisting of a bloated extremely low mass pre-white dwarf (pre-ELM WD) and a compact object with an orbital period of 0.607189~days. The large-amplitude ellipsoidal variations and the evident Balmer and He~I emission lines suggest a filled Roche lobe and ongoing mass transfer. No outburst events were detected in the 15 years of monitoring of J0419, indicating a very low mass transfer rate. The temperature of the pre-ELM, $T_\mathrm{eff} = 5793_{-133}^{+124}\,\rm K$, is cooler than the known ELMs, but hotter than most CV donors. Combining the mean density within the Roche lobe and the radius constrained from our SED fitting, we obtain the mass of the pre-ELM, $M_1 = 0.176\pm 0.014\,M_\odot$. The joint fitting of light and radial velocity curves yields an inclination angle of $i = 66.5_{-1.7}^{+1.4}$ degrees, corresponding to the compact object mass of $M_2 = 1.09\pm 0.05\,M_\odot$. The very bloated pre-ELM has a smaller surface gravity ($\log g = 3.9\pm 0.01$, $R_1 = 0.78 \pm 0.02\,R_\odot$) than the known ELMs or pre-ELMs. The temperature and the luminosity ($L_\mathrm{bol} = 0.62_{-0.10}^{+0.11}\,L_\odot$) of J0419 are close to the main sequence, which makes the selection of such systems through the HR diagram inefficient. Based on the evolutionary model, the relatively long period and small $\log g$ indicate that J0419 could be close to the "bifurcation period" in the orbit evolution, which makes J0419 to be a unique source to connect ELM/pre-ELM WD systems, wide binaries and cataclysmic variables.

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arXiv2022

A dynamically discovered and characterized non-accreting neutron star -- M dwarf binary candidate

Optical time-domain surveys can unveil and characterize exciting but less-explored non-accreting and/or non-beaming neutron stars (NS) in binaries. Here we report the discovery of such a NS candidate using the LAMOST spectroscopic survey. The candidate, designated LAMOST J112306.9+400736 (hereafter J1123), is in a single-lined spectroscopic binary containing an optically visible M star. The star's large radial velocity variation and ellipsoidal variations indicate a relatively massive unseen companion. Utilizing follow-up spectroscopy from the Palomar 200-inch telescope and high-precision photometry from TESS, we measure a companion mass of $1.24_{-0.03}^{+0.03}~M_{\odot}$. Main-sequence stars with this mass are ruled out, leaving a NS or a massive white dwarf (WD). Although a massive WD cannot be ruled out, the lack of UV excess radiation from the companion supports the NS hypothesis. Deep radio observations with FAST yielded no detections of either pulsed or persistent emission. J1123 is not detected in numerous X-ray and gamma-ray surveys. These non-detections suggest that the NS candidate is not presently accreting and pulsing. Our work exemplifies the capability of discovering compact objects in non-accreting close binaries by synergizing the optical time-domain spectroscopy and high-cadence photometry.

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arXiv2022

Formation of Mass-gap Black Holes from Neutron Star X-ray Binaries with Super-Eddington Accretion

Electromagnetic and gravitational wave observations indicate that there is dearth of compact objects with mass $\sim 2.5-5~{\rm M_\odot}$. This so-called "mass gap" may be linked to the supernova explosion mechanisms that produce neutron stars (NSs) and black holes (BHs). However, the existence of a few mass-gap compact objects, some of which have been confirmed to be BHs, poses a challenge to the traditional theory of black hole formation. In this work we investigate the possible formation channel of BHs from accretion-induced collapse (AIC) of NSs in X-ray binaries. In particular, we consider the influence of super-Eddington accretion of NSs. Recent observations of ultraluminous X-ray pulsars suggest that their apparent luminosities may reflect the true accretion luminosities of the accreting NSs, even exceeding the Eddington limit by a factor of $\gtrsim 100$. Thus, NSs accreting at a super-Eddington accretion rate may rapidly grow into BHs in intermediate/low-mass X-ray binaries. Based on the super-Eddington accretion disk models, we have investigated the evolution of NSs in intermediate/low-mass X-ray binaries by combining binary population synthesis and detailed stellar evolutionary calculations. We show that super-Eddington accretion plays a critical role in mass growth of NSs, and the final masses of the descendant BHs are heavily dependent on the NS magnetic fields, the metallicity of the donor star, and the bifurcation period of the binaries. AIC of NSs may account for some of the observed mass-gap BHs like GRO J0422+32. We also present the parameter distributions of the potential mass-gap BHs in a Milky Way-like galaxy, and point out that future space-based gravitational wave observations may provide important test of or constraints on the formation of mass-gap BHs from the AIC channel.

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arXiv2022

A Channel to Form Fast-spinning Black Hole--Neutron Star Binary Mergers as Multi-messenger Sources

After the successful detection of a gravitational-wave (GW) signal and its associated electromagnetic (EM) counterparts from GW170817, neutron star--black hole (NSBH) mergers have been highly expected to be the next type of multi-messenger source. However, despite the detection of several of NSBH merger candidates during the GW third observation run, no confirmed EM counterparts from these sources have been identified. The most plausible explanation is that these NSBH merger candidates were plunging events mainly because the primary BHs had near-zero projected aligned-spins based on GW observations. In view that NSs can be easily tidally disrupted by BHs with high projected aligned-spins, we study an evolution channel to form NSBH binaries with fast-spinning BHs, the properties of BH mass and spin, and their associated tidal disruption probability. We find that if the NSs are born firstly, the companion helium stars would be tidally spun up efficiently, and would thus finally form fast-spinning BHs. If BHs do not receive significant natal kicks at birth, these NSBH binaries that can merge within the Hubble time would have BHs with the projected aligned-spins $χ_{z}\gtrsim0.8$ and, hence, can certainly allow tidal disruption to happen. Even if significant BH kicks are considered for a small fraction of NSBH binaries, the projected aligned-spins of BHs are $χ_z\gtrsim0.2$. These systems can still be disrupted events unless the NSs are very massive. Thus, NS-first-born NSBH mergers would be promising multi-messenger sources. We discuss various potential EM counterparts associated with these systems and their detectability in the upcoming fourth observation run.

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arXiv2022

Stable mass transfer can explain massive binary black hole mergers with a high spin component

Recent gravitational wave observations showed that binary black hole (BBH) mergers with massive components are more likely to have high effective spins. In the model of isolated binary evolution, BH spins mainly originate from the angular momenta of the collapsing cores before BH formation. Both observations and theories indicate that BHs tend to possess relatively low spins, the origin of fast-spinning BHs remains a puzzle. We investigate an alternative process that stable Case A mass transfer may significantly increase BH spins during the evolution of massive BH binaries. We present detailed binary evolution calculations and find that this process can explain observed high spins of some massive BBH mergers under the assumption of mildly super-Eddington accretion.

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arXiv2021

Are there magnetars in high-mass X-ray binaries?

Magnetars form a special population of neutron stars with strong magnetic fields and long spin periods. About 30 magnetars and magnetar candidates known currently are probably isolated. But the possibility that magnetars are in binaries hasn't been excluded. In this work, we perform spin evolution of neutron stars with different magnetic fields in wind-fed high-mass X-ray binaries and compare the spin period distribution with observations, aiming to find magnetars in binaries. Our simulation shows that some of the neutron stars, which have long spin periods or in wide-separation systems, need strong magnetic fields to explain their spin evolution. This implies that there are probably magnetars in high-mass X-ray binaries. Moreover, this can further provide a theoretical basis for some unclear astronomical phenomena, such as the possible origin of periodic fast radio bursts from magnetars in binary systems.

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arXiv2021

Periodic Activities of Repeating Fast Radio Bursts from Be/X-ray Binary Systems

The frequency-dependent periodic active window of the fast radio burst FRB 180916.J0158+65 (FRB 180916B) was observed recently. In this Letter, we propose that a Be/X-ray binary (BeXRB) system, which is composed of a neutron star (NS) and a Be star with a circumstellar disk, might be the source of a repeating FRB with periodic activities, and apply this model to explain the activity window of FRB 180916B. The interaction between the NS magnetosphere and the accreted material results in evolution of the spin period and the centrifugal force of the NS, leading to the change of the stress in the NS crust. When the stress of the crust reaches the critical value, a starquake occurs and further produces FRBs. The interval between starquakes is estimated to be a few days that is smaller than the active window of FRB 180916B. When the NS moves out of the disk of the Be star, the interval between starquakes becomes much longer than the orbital period, which corresponds to the non-active phase. In this model, due to the absorption of the disk of the Be star, a frequency-dependent active window would appear for the FRBs, which is consistent with the observed properties of FRB 180916B. And the contribution of dispersion measure (DM) from the disk of the Be star is small. In addition, the location of FRB 180916B in the host galaxy is consistent with a BeXRB system.

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arXiv2021

Population Synthesis of Black Hole Binaries with Compact Star Companions

We perform a systematic study of merging black hole (BH) binaries with compact star (CS) companions, including black hole--white dwarf (BH--WD), black hole--neutron star (BH--NS) and black hole--black hole (BH--BH) systems. Previous studies have shown that mass transfer stability and common envelope evolution can significantly affect the formation of merging BH--CS binaries through isolated binary evolution. With detailed binary evolution simulations, we obtain easy-to-use criteria for the occurrence of the common envelope phase in mass-transferring BH binaries with a nondegenerate donor, and incorporate into population synthesis calculations. To explore the impact of possible mass gap between NSs and BHs on the properties of merging BH--CS binary population, we adopt different supernova mechanisms involving the \textit{rapid}, \textit{delayed} and \textit{stochastic} prescriptions to deal with the compact remnant masses and the natal kicks. Our calculations show that there are $ \sim 10^{5} -10^{6}$ BH--CS binaries in the Milky Way, among which dozens are observable by future space-based gravitational wave detectors. We estimate that the local merger rate density of all BH--CS systems is $ \sim 60-200 \,\rm Gpc^{-3}yr^{-1}$. While there are no low-mass BHs formed via \textit{rapid} supernovae, both \textit{delayed} and \textit{stochastic} prescriptions predict that $ \sim 100\% $/$ \sim 70\% $/$ \sim 30\% $ of merging BH--WD/BH--NS/BH--BH binaries are likely to have BH components within the mass gap.

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arXiv2021

Evolution of LMXBs under Different Magnetic Braking Prescriptions

Magnetic braking (MB) likely plays a vital role in the evolution of low-mass X-ray binaries (LMXBs). However, it is still uncertain about the physics of MB, and there are various proposed scenarios for MB in the literature. To examine and discriminate the efficiency of MB, we investigate the LMXB evolution with five proposed MB laws. Combining detailed binary evolution calculation with binary population synthesis, we obtain the expected properties of LMXBs and their descendants binary millisecond pulsars. We then discuss the strength and weakness of each MB law by comparing the calculated results with observations. We conclude that the $τ$-boosted MB law seems to best match the observational characteristics.

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arXiv2020

Population Synthesis of Galactic Be-star Binaries with A Helium-star Companion

LB-1 was originally suggested to harbour a very massive ($ \sim 70 M_\odot $) black hole, but was recently suggested to be a post-mass transfer binary containing a Be star and a helium (He) star. In this paper, we use the binary population synthesis method to simulate the potential population of the Be$ - $He binaries in the Milky Way. Mass transfer process during the progenitor binary evolution plays a vital role in determining the possible properties of the Be$ - $He binary population. By constructing a range of physical models with significantly different mass-transfer efficiencies, we obtain the predicted distributions at the current epoch of the component masses and the orbital periods for the Be$ - $He binaries. In particular, we show that, LB-1 very likely has evolved through non-conservative mass transfer if it is indeed a Be$ - $He system. We estimate that there are more than $ 10^{3} $ Be$ - $He binaries with V-band apparent magnitudes brighter than LB-1.

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arXiv2020

Population Synthesis of Black Hole X-Ray Binaries

We present a systematic study of the X-ray binaries (XRBs) containing a black hole (BH) and a non-degenerate companion, in which mass transfer takes place via either capturing the companion's wind or Roche lobe overflow (RLO). As shown in our previous work that focusing on the formation and evolution of detached BH binaries, our assumed models relevant to BH's progenitors predicted significantly different binary properties \citep{sl19}. In this paper, we further follow the evolutionary paths of the BH systems that appearing as XRBs. By use of both binary population synthesis and detailed binary evolution calculations, we can obtain the potential population of BH XRBs. Distributions at the current epoch of various binary parameters have been computed. The observed sample of wind-fed XRBs can be well reproduced under assumption of all our models. The wind-fed XRBs are expected to be so rare ($ \lesssim 100 $) that only a couple of such systems have been detected. Comparison of known RLO XRBs with the calculated distributions of various binary parameters indicates that only the models assuming relatively small masses for BH progenitors can roughly match the observations. Accordingly we estimate that there are hundreds of RLO XRBs in the Milky Way, of which the majority are low-mass XRBs. The RLO systems may become ultraluminous X-ray sources (ULXs) if the BH accretes at a very high rate, we expect that about a dozen ULXs with a BH accretor may exist in a Milky Way$-$like galaxy.

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arXiv2020

On the formation of PSR J1640+2224: a neutron star born massive?

PSR J1640+2224 is a binary millisecond pulsar (BMSP) with a white dwarf (WD) companion. Recent observations indicate that the WD is very likely to be a $\sim 0.7\,M_{\odot}$ CO WD. Thus the BMSP should have evolved from an intermediate-mass X-ray binary (IMXB). However, previous investigations on IMXB evolution predict that the orbital periods of the resultant BMSPs are generally $<40$ days, in contrast with the 175 day orbital period of PSR J1640+2224. In this paper, we explore the influence of the mass of the neutron star (NS) and the chemical compositions of the companion star on the formation of BMSPs. Our results show that, the final orbital period becomes longer with increasing NS mass, and the WD mass becomes larger with decreasing metallicity. In particular, to reproduce the properties of PSR J1640+2224, the NS was likely born massive ($>2.0\,M_{\odot}$).

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