Shi-Jie Gao

Shi-Jie Gao

Postdoc at Nanjing University

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publications

On the magnetic fields of ultraluminous X-ray pulsars

Shi-Jie Gao, Xiang-Dong Li
Research in Astronomy and Astrophysics, 2021
DOI: 10.1088/1674-4527/21/8/196
NASA ADS: 2021RAA....21..196G
arXiv

So far quite a few ultraluminous X-ray (ULX) pulsars have been discovered. In this work, we construct a super-Eddington, magnetic accretion disk model to estimate the dipole magnetic field of eight ULX pulsars based on their observed spin-up variations and luminosities. We obtain two branches of dipole magnetic field solutions. They are distributed in the range of B ~ (0.156 - 64.5) × 1010 G and ~ (0.275 - 79.0) × 1013 G corresponding to the low- and high-B solutions respectively. The low magnetic field solutions correspond to the state that the neutron stars are far away from the spin equilibrium, and the high magnetic field solutions are close to the spin equilibrium. The ultra-strong magnetic fields derived in Be-type ULX pulsars imply that the accretion mode in Be-type ULX pulsars could be more complicated than in the persistent ULX pulsars and may not be accounted for by the magnetized accretion disk model. We suggest that the transition between the accretor and the propeller regimes may be used to distinguish between the low- and high-B magnetic field solutions in addition to the detection of the cyclotron resonance scattering features.

Formation of mass-gap black holes from neutron star X-ray binaries with super-Eddington accretion

Shi-Jie Gao, Xiang-Dong Li, Yong Shao
Monthly Notices of the Royal Astronomical Society, 2022
DOI: 10.1093/mnras/stac1426
NASA ADS: 2022MNRAS.514.1054G
arXiv

Electromagnetic and gravitational wave observations indicate that there is dearth of compact objects with mass ~2.5-5 M☉. 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 ≳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 disc 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.

Impact of asymmetrical mass ejection from proto-white dwarfs on the properties of binary millisecond pulsars

Wen-Shi Tang, Shi-Jie Gao, Xiang-Dong Li
Monthly Notices of the Royal Astronomical Society, 2022
DOI: 10.1093/mnras/stac3615
NASA ADS: 2023MNRAS.519.2951T
arXiv

The standard formation theory of binary millisecond pulsars (BMSPs) predicts efficient orbital circularization due to tidal interaction during the previous mass transfer phase. Therefore, BMSPs are expected to have a circular orbit. However, the discovery of several eccentric BMSPs (eBMSPs) with a white dwarf (WD) companion has challenged this picture. In particular, recent observation reveals that the spin angular momentum of the eBMSP J0955-6150 is tilted at an angle >4.8○ from the orbital angular momentum. This is the first time that a tilt angle is deduced for eBMSPs, which provides an important clue to their formation mechanism. Both the orbital eccentricity and the tilt angle could be qualitatively accounted for by asymmetrical mass ejection during thermonuclear flashes from proto-WDs (so-called thermonuclear rocket model), but detailed studies are still lacking. In this paper, we simulate the impact of the kick caused by asymmetrical mass ejection on the properties of BMSPs. We find that the thermonuclear rocket model can potentially explain the observational characteristics of both eBMSPs and normal BMSPs under reasonable input parameters. In addition, our results predict a wide range of the orbital period (from less than one day to more than several hundred days) for eBMSPs, which can be tested by future observations.

Detection Prospects of Fast-merging Gravitational Wave Sources in M31

Jian-Guo He, Yong Shao, Shi-Jie Gao, Xiang-Dong Li
The Astrophysical Journal, 2023
DOI: 10.3847/1538-4357/ace348
NASA ADS: 2023ApJ...953..153H
arXiv

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 first 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 ~2 minutes for double white dwarfs to ~20 minutes for double black holes.

The white dwarf mass-orbital period relation under wind mass-loss

Shi-Jie Gao, Xiang-Dong Li
Monthly Notices of the Royal Astronomical Society, 2023
DOI: 10.1093/mnras/stad2446
NASA ADS: 2023MNRAS.525.2605G
arXiv

Helium white dwarfs (HeWDs) are thought to form from low-mass red giant stars experiencing binary interaction. Because the helium core mass of a red giant star is closely related to the stellar radius, there exists well-known relation between the orbital period (Porb) and the mass (MWD) of the HeWDs, which is almost independent of the type of the companion star. Traditional derivation of the MWD-Porb relation generally neglected the effect of wind mass-loss from the red giants, while observations show that wind mass-loss from red giants in binary systems is systematically higher than that from isolated stars. In this work, we calculate binary evolution with tidally enhanced stellar wind (TEW) and find that it causes significantly scatter of the traditional MWD-Porb relation. The TEW can prevent the red giants from overflowing their Roche lobes and slow down the growth of the helium core, leaving a lower mass HeWD for given orbital period. This scenario may account for some of the HeWD binaries that deviate from the traditional MWD-Porb relation. However, we point out that observations of more HeWD binaries in wide orbits are needed to test the TEW model and to constrain the enhanced wind factor.

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

Shi-Jie Gao, Xiang-Dong Li
The Astrophysical Journal, 2023
DOI: 10.3847/1538-4357/ace890
NASA ADS: 2023ApJ...956..128G
arXiv

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.

A potential mass-gap black hole in a wide binary with a circular orbit

Song Wang, Xinlin Zhao, Fabo Feng, Hongwei Ge, Yong Shao, Yingzhen Cui, Shi-Jie Gao, Lifu Zhang, et al.
Nature Astronomy, 2024
DOI: 10.1038/s41550-024-02359-9
NASA ADS: 2024NatAs...8.1583W
arXiv

The mass distribution of black holes identified through X-ray emission suggests a paucity of black holes in the mass range of 3 to 5 solar masses. Modified theories have been devised to explain this mass gap, and it is suggested that natal kicks during a supernova explosion can more easily disrupt binaries with lower-mass black holes. Although recent Laser Interferometer Gravitational-Wave Observatory observations reveal the existence of compact remnants within this mass gap, the question of whether low-mass black holes can exist in binaries remains a matter of debate. Such a system is expected to be non-interacting and without X-ray emission, and can be searched for using radial-velocity and astrometric methods. Here we report on Gaia Data Release 3 (DR3) 3425577610762832384, which is a wide binary system that includes a red giant star and an unseen object, exhibiting an orbital period of approximately 880 days and a near-zero eccentricity. Through the combination of radial-velocity measurements from the Large Aperture Multi-Object Spectroscopic Telescope and astrometric data from Gaia DR2 and DR3 catalogues, we determine a mass of 3 .6‒0.5+0.8M☉ <![CDATA[\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$3.{6}_{-0.5}^{+0.8} {M}_{\odot }$$]]> of the unseen component. If the unseen companion is a black hole, its mass would fall within the gap and it would strongly suggest the existence of binary systems containing low-mass black holes. More notably, the formation of its surprisingly wide circular orbit challenges current binary evolution and supernova explosion theories.

Discovery of a Millisecond Pulsar Associated with Terzan 6

Shi-Jie Gao, Yi-Xuan Shao, Pei Wang, Ping Zhou, Xiang-Dong Li, Lei Zhang, Joseph W. Kania, Duncan R. Lorimer, et al.
The Astrophysical Journal Letters, 2024
DOI: 10.3847/2041-8213/ad7a69
NASA ADS: 2024ApJ...974L...2G
arXiv

Observations show that globular clusters (GCs) might be among the best places to find millisecond pulsars (MSPs). However, the GC Terzan 6 seems to be an exception without any pulsar discovered, although its high stellar encounter rate suggests that it harbors dozens of them. We report the discovery of the first radio pulsar, PSR J1750─3116A, likely associated with Terzan 6 in a search of C-band (4─8 GHz) data from the Robert C. Byrd Green Bank Telescope with a spin period of 5.33 ms and dispersion measure (DM) ≃ 383 pc cm-3. The mean flux density of this pulsar is approximately 3 μJy. The DM agrees well with predictions from the Galactic free electron density model, assuming a distance of 6.7 kpc for Terzan 6. PSR J1750─3116A is likely an isolated MSP, potentially formed through dynamical interactions, considering the core-collapsed classification and the exceptionally high stellar encounter rate of Terzan 6. This is the highest radio frequency observation that has led to the discovery of a pulsar in a GC to date. While L-band (1─2 GHz) observations of this cluster are unlikely to yield significant returns due to propagation effects, we predict that further pulsar discoveries in Terzan 6 will be made by existing radio telescopes at higher frequencies.

Instability in Supernova Fallback Disks and Its Effect on the Formation of Ultralong Period Pulsars

Hao-Ran Yang, Xiang-Dong Li, Shi-Jie Gao, Kun Xu
The Astrophysical Journal, 2024
DOI: 10.3847/1538-4357/ad83d4
NASA ADS: 2024ApJ...976...77Y
arXiv

Several pulsars with unusually long periods were discovered recently, comprising a potential population of ultralong period pulsars (ULPPs). The origin of their long periodicity is not well understood, but may be related to magnetars spun down by surrounding fallback disks. While there are few systematic investigations on the fallback-disk-assisted evolution of magnetars, instability in the disk has received little attention, which determines the lifetime of the disk. In this work we simulate the evolution of the magnetic field, spin period, and magnetic inclination angle of magnetars with a supernova fallback disk. We find that a thermal viscous instability in the disk could significantly affect the formation of ULPPs. Our simulation results also reveal that a large fraction of ULPPs seem to be nearly aligned and orthogonal rotators. This might help place ULPPs above the death line in the pulse period─period derivative plane. However, some extra mechanisms seem to be required to account for the radio emission of ULPPs.

Exploring Field-evolution and Dynamical-capture Coalescing Binary Black Holes in GWTC-3

Yin-Jie Li, Shao-Peng Tang, Shi-Jie Gao, Dao-Cheng Wu, Yuan-Zhu Wang
The Astrophysical Journal, 2024
DOI: 10.3847/1538-4357/ad83b5
NASA ADS: 2024ApJ...977...67L
arXiv

We investigate formation channels for merging binary black holes (BBHs) in GWTC-3, with a dedicated semiparametric population model. The model first describes or excludes a high-spin (with magnitudes of ∼0.7) and high-mass (ranging in ∼20─80M ⊙) subpopulation, which was identified by previous works and can be interpreted as hierarchical mergers. We find that the rest of BBH population can be categorized into two subpopulations with different mass and mass-ratio distributions, as indicated by a Bayes factor of . One subpopulation, characterized by nearly aligned spins and consistent with isolated field formation, likely dominates the 10-solar-mass peak in the primary-mass function. The other subpopulation, with isotropic spins and consistent with the dynamical channels, shows a stronger preference for symmetric pairing, and mainly contributes to the 35-solar-mass peak in the primary-mass function. Note that the Bayes factor is not high enough with the currently available data, so that the case of a single population is still acceptable. Additionally, we compare the mass distributions between merging BBHs and black holes (BHs) in high-mass X-ray binaries (HMXBs). We find that the primary mass of the aligned subpopulation is slightly lighter than those of the HMXB BHs, while the isotropic subpopulation is consistent with the HMXB BHs, if the power-law index of its mass function is shifted by 2, as indicated by the dynamical formation channels. However, the spin magnitudes of both subpopulations are significantly smaller than those of the HMXB BHs.

Probing Cosmology with 92 Localized Fast Radio Bursts and DESI BAO

Yi-Ying Wang, Shi-Jie Gao, Yi-Zhong Fan
The Astrophysical Journal, 2025
DOI: 10.3847/1538-4357/adade8
NASA ADS: 2025ApJ...981....9W
arXiv

Recent baryon acoustic oscillation (BAO) measurements from the Dark Energy Spectroscopic Instrument (DESI) collaboration, combined with the cosmic microwave background (CMB) and type Ia supernovae observations, suggest a preference for dynamical dark energy (DDE) with w0 > -1 and wa < 0. Given the cosmological origin of fast radio bursts (FRBs), the combination of their dispersion measures (DMs) and host galaxy redshifts makes localized FRBs a valuable tool for probing cosmology. Using an updated sample of 92 localized FRBs, along with DESI BAO, PlantheonPlus, and CMB data, we constrain the dark energy (DE) equation of state (EoS) under the Chevallier─Polarski─Linder parameterization. We find that even without incorporating CMB data, DDE remains preferred with and at a confidence level of ∼2.5σ. A joint analysis constrains these to be and , showing a discrepancy with ΛCDM at a ∼3.1σ level. Furthermore, using localized FRBs alone, we estimate the Hubble constant H0 to be and , assuming the Galactic electron density models to be NE2001 and YMW16, respectively. Thus, accurate accounting of the Galactic DM is crucial for resolving the Hubble tension with FRBs. Future BAO measurements, next-generation CMB experiments, and more localized FRBs will further constrain the DE EoS and the cosmological parameters.

A Target Search for Fast Radio Bursts Associated with Two Fast Blue Optical Transients: AT2018cow and CSS161010

Shi-Jie Gao, Xiang-Dong Li, Yi-Xuan Shao, Ping Zhou, Pei Wang, Yun-Wei Yu, Zhen Yan, Di Li
The Astrophysical Journal, 2025
DOI: 10.3847/1538-4357/adf732
NASA ADS: 2025ApJ...990...93G
arXiv

Fast blue optical transients (FBOTs) are luminous, rapidly evolving events with blue spectra, possibly powered by newborn magnetars and linked to fast radio bursts (FRBs). Given this potential connection, we conducted deep radio observations of two nearby FBOTs (AT2018cow and CSS161010) using the Five-hundred-meter Aperture Spherical radio Telescope, but detected no FRB-like signals. Our observations establish the most stringent upper limits on millisecond radio transients from FBOTs, reaching ∼10 mJy flux density. Assuming a log-normal luminosity function analogous to the repeating FRB 121102, we constrain the burst rate from potential magnetars in FBOTs to < 0.01 hr-1. The short ejecta escape timescale (∼2.6 yr) compared to our observation epochs (4-6 yr post-explosion) suggests that nondetection may not be attributed to FBOT's ejecta absorption. These findings impose useful constraints on the FRB activity emanating from newborn magnetars within FBOTs. They indicate that if there is a burst phase, it is either characterized by weaker bursts, occurs less frequently compared to those in known repeating FRB sources, or takes place beyond the time frame of our current observations. To gain deeper insights into the birth-related activity of magnetars, it is of importance to conduct timely and sustained FRB searches in FBOTs that emerge in the future.

A Two-stage Kick Scenario for the Peculiar Low-mass X-Ray Binary GX 1+4

Xiangyu Ivy Wang, Shi-Jie Gao, Xiang-Dong Li
The Astrophysical Journal Letters, 2025
DOI: 10.3847/2041-8213/ae060a
NASA ADS: 2025ApJ...991L..37W
arXiv

The low-mass X-ray binary (LMXB) GX 1+4 stands out with its unique properties. Despite being an old system, it hosts a strongly magnetized neutron star (NS), a trait usually linked to younger systems. Its exceptionally long orbital period (1160 days) and low eccentricity (0.101) imply that the NS formed with minimal mass loss and a weak natal kick. These features collectively point toward the NS having formed through the accretion-induced collapse (AIC) of a white dwarf. However, GX 1+4's unusually high peculiar velocity (∼189.36 km s-1) defies standard AIC explanations. To address this discrepancy, we propose a two-stage kick scenario within the AIC framework: an initial natal kick followed by a delayed electromagnetic "rocket effect" kick. Our Monte Carlo simulations indicate that while the natal kick (≲100 km s-1) can generate a wide range of orbital eccentricities, the subsequent rocket kick (∼240─480 km s-1) explains both the high systemic velocity and low eccentricity. This two-stage kick mechanism naturally reproduces the observed characteristics of GX 1+4, provided that the NS's initially buried magnetic field reemerges after the acceleration process ends. Our study represents the first attempt to quantitatively constrain the kick velocities in GX 1+4 and underscores the importance of possible rocket kicks in forming such peculiar LMXB systems.

RRAT J2325─0530: A Rotating Radio Transient with an Atypical Waiting-time Distribution

Shi-Jie Gao, Xiang-Dong Li, Zhen Yan, Yi-Xuan Shao, Ping Zhou
The Astrophysical Journal, 2025
DOI: 10.3847/1538-4357/adff5b
NASA ADS: 2025ApJ...991..201G
arXiv

We present 1.25 GHz observations of the rotating radio transient (RRAT) J2325─0530, conducted with the Five-hundred-meter Aperture Spherical radio Telescope. Approximately 60% of detected single pulses occur in clusters of two to five consecutive bursts. Consequently, the waiting-time distribution between successive single pulses exhibits a pronounced excess at one rotation period, deviating from the exponential distribution expected for a Poisson process. After grouping consecutive bursts into single emission events, the recalculated waiting-time distribution is well described by a Weibull distribution with a shape parameter k ≳ 1. Monte Carlo simulations incorporating both intrinsic burst on-windows and rotational modulation successfully reproduce the observed one-rotation excess. These results suggest that RRAT J2325─0530 emits through a quasi-random process with on-windows slightly longer than its spin period, modulated by the rotation of the emission beam. Additionally, the polarization position angle shows complex behavior that cannot be fully described by the standard rotating vector model, and several pulses exhibit quasiperiodic microstructures. Taken together, these features indicate complex magnetospheric dynamics underlying the sporadic emission behavior of RRAT J2325─0530.

Formation of Recycled Pulsars in Common Envelope Binaries

Yu-Dong Nie, Yong Shao, Jian-Guo He, Ze-Lin Wei, Shi-Jie Gao, Xiao-Jie Xu, Xiang-Dong Li
The Astrophysical Journal, 2026
DOI: 10.3847/1538-4357/ae3569
NASA ADS: 2026ApJ...997..265N
arXiv

We present a systematic study of the evolution of low- and intermediate-mass X-ray binaries consisting of a 1.4 M⊙ neutron star (NS) and a donor star of mass 1─8 M⊙. Using grids of detailed MESA simulations, we show that for donor masses of 2─8 M⊙, mass transfer may be dynamically unstable, leading to a common envelope (CE) phase. By adopting CE ejection efficiencies in the range αCE = 0.3─3.0, we find that post-CE binaries frequently experience a CE decoupling phase (CEDP), which plays a critical role in determining their final orbital and compositional properties. Systems with initial donor masses ≳3.5 M⊙ predominantly evolve into NS binaries with carbon─oxygen or oxygen─neon white dwarfs (WDs) with masses between 0.5 and 1.4 M⊙. Comparison with the observed population of binary pulsars with a WD companion shows better agreement with higher CE ejection efficiencies (αCE = 3.0). Furthermore, we demonstrate that NSs can accrete a sufficient amount of matter (≳0.01 M⊙) during the CEDP and subsequent Case BA/BB/BC mass transfer phases to be effectively recycled into millisecond pulsars. We identify two distinct evolutionary channels capable of reproducing the observed characteristics of the millisecond pulsar PSR J1928+1815 with a helium-star companion. Our results highlight the importance of the CEDP in the formation of recycled pulsars and provide constraints on the CE ejection efficiency during binary evolution.

Pulsar Gleaners: Discovery of 19 Pulsars in FAST Archival Data at |b| < 5° and Decl. < -5°

Shi-Jie Gao, Yi-Xuan Shao, Xiang-Dong Li
The Astrophysical Journal, 2026
DOI: 10.3847/1538-4357/ae3243
NASA ADS: 2026ApJ...997..210G
arXiv

We report the discovery of 19 new pulsars identified from archival observations of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) within Galactic latitudes |b| < 5° and declinations decl. < -5°. The dataset was recorded using FAST's L-band 19 beam receiver and covered ∼3.6 deg2 with a cumulative integration time of ∼500 hr and a total raw data volume of ∼700 TB. Our search employed fast Fourier transform (FFT)─based and fast folding algorithm (FFA)─based periodic searches and the single-pulse search. These new pulsars have spin periods ranging from 0.03 to 5.54 s. Two have periods under 0.1 s, suggesting they are likely young pulsars or mildly recycled pulsars. Four pulsars exhibit dispersion measures (DMs) exceeding 1000 pc cm-3, with PSR J1839─0558t having the highest value in our sample at ∼1271 pc cm-3, providing valuable samples for pulsar studies in the high-DM regime. Two rotating radio transients, PSRs J1836─0552t and J1847─0624t, were detected by FFA and single-pulse searches but failed with the FFT-based searches. In addition, three faint pulsars that were also missed by FFT-based searches were successfully detected using FFA. These discoveries demonstrate the critical role of FFA in uncovering faint, long-period, and sporadic pulsars and highlight the significant potential of FAST archival data, especially when combined with longer integration times and complementary search techniques, to reveal rare and weak pulsar populations. The term "gleaners" in the title "Pulsar Gleaners" originates from the 1857 oil painting The Gleaners by Jean-François Millet, which depicts three peasant women collecting stray stalks of wheat left in a field after the harvest.

Search for Radio Pulsations from Neutron Star Candidates in Detached Binaries

Shi-Jie Gao, Xiang-Dong Li, Song Wang, Kareem El-Badry, De-Jiang Zhou, Yi-Xuan Shao, Zhen Yan, Pei Wang, et al.
The Astrophysical Journal, 2026
DOI: 10.3847/1538-4357/ae2616
NASA ADS: 2026ApJ...997..222G
arXiv

Recent optical astrometric and spectroscopic surveys have identified numerous neutron star (NS) candidates in nonaccreting detached binary systems, but their compact-object nature remains unconfirmed. In this work, we present targeted radio observations of 31 such candidates using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), the Robert C. Byrd Green Bank Telescope, and the Shanghai TianMa Radio Telescope. Over a total of 46.65 hr of observing time, we detected neither periodic nor single-pulse radio emissions. These nondetections place stringent upper limits on the flux densities of any potential radio signals, reaching ∼4 μJy for periodic emission and ∼10 mJy for single pulses with FAST. Since our observations are highly sensitive and the flux density upper limits are well below the median fluxes of known Galactic pulsars, this suggests that geometric beaming is the most likely explanation for the nondetections if these objects are indeed pulsars. Alternatively, the NSs may be sufficiently old (≳10 Gyr) and have become intrinsically radio-quiet. In this case, our findings highlight the inherent difficulty of confirming NSs in such old detached binary systems through radio pulsation searches.

Polar mounds on strangeon stars: the neutrino emission from ultraluminous X-ray pulsars

Hong-Bo Li, Shi-Jie Gao, Xiang-Dong Li, Ren-Xin Xu
Monthly Notices of the Royal Astronomical Society, 2026
DOI: 10.1093/mnras/stag241
NASA ADS: 2026MNRAS.546ag241L
arXiv

Ultraluminous X-ray pulsars (ULXPs) serve as unique astrophysical laboratories, offering critical insights into accretion physics under extreme conditions, such as strong magnetic fields and super-Eddington accretion rates. Additionally, the nature of pulsars, i.e. the equation of state of supranuclear matter, is still a matter of intense debate, basing on either conventional neutron stars or strange stars. In this work, in order to differentiate the conjectured states of matter, we investigate accretion columns of ULXPs based on the strangeon-star (SS) model, focusing on the thermal mound at the column base. Accounting for Coulomb and strangeness barriers of SSs, we find that the mound can reach $0.7\text{-}0.95\, \rm km$ in height with temperatures above $10^9\, \rm K$, enabling substantial neutrino emission via electron─positron annihilation. At low-accretion rates (${\lt} 10^{20}\, \rm g\, s^{-1}$), photons dominate the luminosity, while at higher rates (${\gt} 10^{21}\, \rm g\, s^{-1}$), photon trapping makes neutrino emission the main cooling channel, with total luminosity exceeding photon emission, which saturates near $10^{41}\, \rm erg\, s^{-1}$. Even though the predicted neutrino flux from the nearest system, Swift J0243.6$+$6124, lies well below the diffuse MeV background ─ implying that detectable emission would require substantially closer or more luminous sources ─ these results demonstrate the key role of the thermal mound and SS properties in accretion, providing a foundation for future ULXP studies and suggesting that neutrino observations could, in principle, offer a novel probe of SSs and extreme supranuclear matter.

The Orbital Parameters of Gamma-Ray Binary PSR J2032+4127

Yu-Feng Luo, Shan-Shan Weng, Qing-Zhong Liu, Ming-Yu Ge, Han-Long Peng, Shi-Qi Zhou, Shi-Jie Gao, Yu-Jia Zheng, et al.
The Astrophysical Journal, 2026
DOI: 10.3847/1538-4357/ae4006
NASA ADS: 2026ApJ...998..332L
arXiv

PSR J2032+4127 is the only gamma-ray binary that exhibits pulsations in gamma rays. Previous research has indicated that the pulsar and the Be star MT91 213 orbit each other in a highly eccentric orbit with an extremely long period, with the pulsar reaching its periastron on 2017 November 13. Since its launch, the Fermi satellite has been monitoring this pulsar for 16 yr, covering the 8 yr before and the 8 yr after the pulsar passed its periastron. Using these data, we present an analysis of pulse arrival times and precisely determine the orbital parameters for the first time: the orbital period of Porb ∼ 52.3 yr, the eccentricity of e ∼ 0.98, the semimajor axis of asini ∼ 25.3 au, and the orbital inclination of ∼47 .° 1─55 .° 1. We also reveal another small glitch occurred in 2021, MJD ∼ 59500.

talks

teaching

Teaching experience 1

Undergraduate course, University 1, Department, 2014

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Teaching experience 2

Workshop, University 1, Department, 2015

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