arXiv subjects

Lijing Shao

Publications and source records attributed to Lijing Shao.

At least 55 records · Page 3Linked to original sources

arXiv2025

Galactic double neutron stars as dual-line gravitational-wave sources: Prospects with LISA and Cosmic Explorer

Double neutron star (DNS) systems could serve as intriguing dual-line gravitational-wave (GW) sources, emitting both high- and low-frequency GWs, arising respectively from the asymmetric spinning bodies of individual neutron stars (NSs) and the binary orbital inspiral. Detecting such dual-line signals could provide novel perspectives on binary orbital geometry and NS internal physics. We expand upon previously calculated spinning NS waveforms by incorporating higher-order terms of NS structural parameters. A population simulation is performed for spinning NS components in DNS systems potentially detectable by the space-based Laser Interferometer Space Antenna (LISA). Based on 4-year LISA observation of 35 resolvable DNS systems under an optimistic scenario, we estimate that 6 (22) spinning NS components could be detected by the next-generation ground-based GW detector, Cosmic Explorer, under log-uniform (uniform) sampling of NS structural parameters. For these dual-line sources, the median signal-to-noise ratio achievable with Cosmic Explorer is approximately 20--30. Through the dual-line GW detection strategy, the relative measurement accuracy of the NS moment of inertia is estimated to be $\sim 8\%$.

gr-qc↗

arXiv2025

The FAST Globular Cluster Pulsar Survey (GC FANS)

By January 2025, 60 pulsars were discovered by the Five-hundred-meter Aperture Spherical radio Telescope globular cluster (GC) pulsar survey (GC FANS), with spin periods spanning 1.98 ms to 3960.72 ms. Of these, 55 are millisecond pulsars (MSPs; $P<30$ ms), while 34 are binaries with orbital periods spanning 0.12 days to 466.47 days. This paper describes GC FANS, a deep, thorough search for pulsars in 41 GCs in the FAST sky ($-14^\circ < δ< 65^\circ$) and describes new discoveries in 14 of them. We present updated timing solutions for M92A, NGC 6712A, M71A, and M71E, all of which are ``spider'' pulsars with short orbital periods. We present new timing solutions for M71B, C, and D. With orbital periods of $\sim$466 and 378 days, M71B and M71C are the widest known GC binaries; these systems resemble the normal wide MSP-He WD systems in the Galactic disk. With a spin period of 101 ms, M71D is in an eccentric ($e\sim$0.63) orbit with an 11-day period and a massive companion; the system has a total mass of $2.63 \pm 0.08 \, M_{\odot}$. These features and its large characteristic age suggest it is a double neutron star system (DNS) formed via massive binary evolution early in the cluster's history, akin to Galactic disk DNSs--unlike other candidate GC DNSs, which typically form dynamically. A comparative analysis of GC pulsar populations within FAST's sky reveals that most clusters (10 of 14) resemble the Galactic disk MSP population, likely due to lower stellar densities.

astro-ph.HE↗

arXiv2025

First Constraint on Axion-Photon Coupling $g_γ$ from Neutron Star Observations

We propose a novel method to detect axions which uniquely depends on the dimensionless axion-photon coupling $g_γ$, independent of the suppressive axion decay constant $f_a$. Using neutron star PSR B1919+21 data from the Five-hundred-meter Aperture Spherical Telescope, we derive the first constraint $|g_γ|<0.93$ at $1σ$ confidence level for ultra-light axions ($m_a < 10^{-11}$ eV).

hep-ph↗

arXiv2025

Seeking the nearest neutron stars using a new local electron density map

Neutron stars provide a compelling testing ground for gravity, nuclear dynamics, and physics beyond the Standard Model, and so it will be useful to locate the neutron stars nearest to Earth. To that end, we revisit pulsar distance estimates extracted from the dispersion measure of pulsar radio waves scattering on electrons. In particular, we create a new electron density map for the local kiloparsec by fitting to parallax measurements of the nearest pulsars, which complements existing maps that are fit on the Galactic scale. This ``near-Earth'' electron density map implies that pulsars previously estimated to be 100-200 pc away may be as close as tens of parsecs away, which motivates a parallax-based measurement campaign to follow-up on these very-near candidate pulsars. Such nearby neutron stars would be valuable laboratories for testing fundamental physics phenomena, including several late-stage neutron star heating mechanisms, using current and forthcoming telescopes. We illustrate this by estimating the sensitivities of the upcoming Extremely Large Telescope and Thirty Meter Telescope to neutron stars heated by dark matter capture.

astro-ph.HE↗

arXiv2025

Shared Properties of Merger-driven Long-duration Gamma-Ray Bursts

The recent detections of bright optical/infrared kilonova signals following two long-duration gamma-ray bursts (LGRBs), GRB 211211A and GRB 230307A, have significantly challenged the traditional classification of GRBs. These merger-driven LGRBs may represent a distinct GRB population. Since traditional GRB classification methods often struggle to distinguish merger-driven LGRBs from traditional merger-driven short-duration GRBs resulting from compact object mergers and collapse-driven LGRBs produced by massive stars, this work aims to explore the shared properties in terms of hardness, energy, and duration among currently observed merger-driven LGRB events, thereby identifying their observed differences from the traditional GRB population. We collect a sample of merger-driven LGRBs with known redshifts, including observed information on their main emission (ME) and whole emission (WE) phases. Treating ME and WE properties as two independent sets of information, we apply several GRB classification methodologies to explore their potential shared properties. Using the phenomenologically defined Energy-Hardness (EH) parameter, we identify a probable universal linear correlation across merger-driven LGRBs, regardless of whether their ME or WE phases are considered. We propose that such shared properties of merger-driven LGRBs are unlikely to arise from the low-redshift selection effect and they become particularly intriguing when compared with the relatively weak correlations or lack of correlation observed in traditional merger-driven short-duration GRBs (with or without extended emissions) and collapse-driven LGRBs. Our newly proposed correlation highlights the necessity for further investigation into the observations of merger-driven LGRBs and the physical mechanisms underlying the empirical correlation.

astro-ph.HE↗

arXiv2025

Scalarized neutron stars in massive scalar-tensor gravity: X-ray pulsars and tidal deformability

Neutron stars (NSs) in scalar-tensor theories of gravitation with the phenomenon of spontaneous scalarization can develop significant deviations from general relativity. Cases with a massless scalar were studied widely. Here we compare the NS scalarizations in the Damour--Esposito-Far{è}se theory, the Mendes-Ortiz theory, and the $ξ$-theory with a massive scalar field. Numerical solutions for slowly rotating NSs are obtained. They are used to construct the X-ray pulse profiles of a pair of extended hot spots on the surface of NSs. We also calculate the tidal deformability for NSs with spontaneous scalarization which is done for the first time with a massive scalar field. We show the universal relation between the moment of inertia and the tidal deformability. The X-ray pulse profiles, the tidal deformability, and the universal relation may help to constrain the massive scalar-tensor theories in X-ray and gravitational-wave observations of NSs, including the Neutron star Interior Composition Explorer (NICER) satellite, Square Kilometre Array (SKA) telescope, and LIGO/Virgo/KAGRA laser interferometers.

gr-qc↗

arXiv2025

Reanalyzing the ringdown signal of GW150914 using the F-statistic method

The ringdown phase of a gravitational wave (GW) signal from a binary black hole merger provides valuable insights into the properties of the final black hole and serves as a critical test of general relativity in the strong-field regime. A key aspect of this investigation is to determine whether the first overtone mode exists in real GW data, as its presence would offer significant implications for our understanding of general relativity under extreme conditions. To address this, we conducted a reanalysis of the ringdown signal from GW150914, using the newly proposed F-statistic method to search for the first overtone mode. Our results are consistent with those obtained through classical time-domain Bayesian inference, indicating that there is no evidence of the first overtone mode in the ringdown signal of GW150914. However, our results show the potentiality of utilizing the F-statistic methodology to unearth nuanced features within GW signals, thereby contributing novel insights into black hole properties.

gr-qc↗

arXiv2025

Effects of orbital eccentricity on continuous gravitational waveforms from triaxially deformed precessing neutron stars in tight binaries

The successful detection of continuous gravitational waves from spinning neutron stars (NSs) will shape our understanding of the physical properties of dense matter under extreme conditions. Binary population synthesis simulations show that forthcoming space-borne gravitational wave detectors may be capable of detecting some tight Galactic double NSs with 10-min orbital periods. Successfully searching for continuous waves from the individual NS in such a close binary demands extremely precise waveform templates considering the interaction between the NS and its companion. Unlike the isolated formation channel, double NS systems from the dynamical formation channel have moderate to high orbital eccentricities. To accommodate these systems, we generalize the analytical waveforms from triaxial nonaligned NSs under spin-orbit coupling derived by Feng \textit{et al.} [\href{https://journals.aps.org/prd/abstract/10.1103/PhysRevD.108.063035}{Phys. Rev. D 108, 063035 (2023)}] to incorporate the effects of the orbital eccentricity. Our findings suggest that for binaries formed through isolated binary evolution, the impact of eccentricity on the continuous waves of their NSs can be neglected. In contrast, for those formed through dynamical processes, it is necessary to consider eccentricity, as high-eccentricity orbits can result in a fitting factor of $\lesssim 0.97$ (0.9) within approximately 0.5 (1) to 2 (5) yr of a coherent search (at wave frequencies of 100 and 200 Hz). Once the continuous waves from spinning NSs in tight binaries are detected, the relative measurement accuracy of eccentricity can reach $Δe / e \sim O(10^{-7})$ for a signal-to-noise ratio of $O(100)$ based on the Fisher information matrix, bearing significant implications for understanding the formation mechanisms of double NS systems.

gr-qc↗

arXiv2025

Probing intermediate-mass black hole binaries with the Lunar Gravitational-wave Antenna

New concepts for observing the gravitational waves (GWs) using a detector on the Moon, such as the Lunar Gravitational-wave Antenna (LGWA), have gained increasing attention. By utilizing the Moon as a giant antenna, the LGWA is expected to detect GWs in the frequency range from 1 millihertz (mHz) to several hertz, with optimal sensitivity in the decihertz band. Despite the debated formation and evolution channel of intermediate-mass black holes (IMBHs) with masses in the range of $[10^2, 10^5]\ {\rm M_\odot}$, binary systems containing at least one IMBH are widely believed to generate GWs spanning from mHz to a few Hz, making them a key scientific target for the LGWA. We explore the detectability of IMBH binaries with the LGWA in this work. The LGWA is more sensitive to nearby binaries (i.e. with redshift $z\lesssim0.5$) with the primary mass $m_1 \in [10^4, 10^5] \ {\rm M_\odot}$, while it prefers distant binaries (i.e. $z \gtrsim 5$) with $m_1 \in [10^3, 10^4] \ {\rm M_\odot}$. Considering a signal-to-noise ratio threshold of 10, our results imply that the LGWA can detect IMBH binaries up to $z \sim \mathcal{O}(10)$. We further show that the LGWA can constrain the primary mass with relative errors $\lesssim 0.1\%$ for binaries at $z \lesssim 0.5$. Furthermore, we show that the IMBH binaries at $z \lesssim 0.1$ can be used to constrain redshift with relative errors $\lesssim 10\%$, and those with $m_1 \in [10^4, 10^5] \ {\rm M_\odot}$ can be localized by the LGWA to be within $\mathcal{O} (10)$ $\rm deg^2$.

astro-ph.HE↗

arXiv2025

A practical Bayesian method for gravitational-wave ringdown analysis with multiple modes

Gravitational-wave (GW) ringdown signals from black holes (BHs) encode crucial information about the gravitational dynamics in the strong-field regime, which offers unique insights into BH properties. In the future, the improving sensitivity of GW detectors is to enable the extraction of multiple quasi-normal modes (QNMs) from ringdown signals. However, incorporating multiple modes drastically enlarges the parameter space, posing computational challenges to data analysis. Inspired by the $F$-statistic method in the continuous GW searches, we develope an algorithm, dubbed as FIREFLY, for accelerating the ringdown signal analysis. FIREFLY analytically marginalizes the amplitude and phase parameters of QNMs to reduce the computational cost and speed up the full-parameter inference from hours to minutes, while achieving consistent posterior and evidence. The acceleration becomes more significant when more QNMs are considered. Rigorously based on the principle of Bayesian inference and importance sampling, our method is statistically interpretable, flexible in prior choice, and compatible with various advanced sampling techniques, providing a new perspective for accelerating future GW data analysis.

gr-qc↗

arXiv2024

Continuous gravitational waves from thermal mountains on accreting neutron stars: effect of the nuclear pasta phase

As density increases, the shape of nuclei transitions to non-spherical ``nuclear pasta" structures. The physical properties of the nuclear pasta, such as thermal conductivity and elasticity, have implications for detecting continuous gravitational waves from a rapidly rotating neutron star. In this work, we investigate the effect of the nuclear pasta on the quadruple moment, and find out that, compared with previous work, the quadrupole moment contributing to continuous gravitational-wave radiation can be up to two orders of magnitude larger. We also discuss the relationship between the quadruple moment and the maximum shear strain. Considering the properties of nuclear pasta, we study the detectability of known accreting neutron stars and compare predicted results to the detectable amplitude limits. These sources are well above the sensitivity curves for Cosmic Explorer and Einstein Telescope detectors. Our work advances the understanding of the properties of nuclear pasta and a possible mechanism for continuous gravitational waves.

gr-qc↗

arXiv2024

Measuring the Spin of the Galactic Center Supermassive Black Hole with Two Pulsars

As a key science project of the Square Kilometre Array (SKA), the discovery and timing observations of radio pulsars in the Galactic Center would provide high-precision measurements of the spacetime around the supermassive black hole, Sagittarius A* (Sgr A*), and initiate novel tests of general relativity. The spin of Sgr A* could be measured with a relative error of $\lesssim 1\%$ by timing one pulsar with timing precision that is achievable for the SKA. However, the real measurements depend on the discovery of a pulsar in a very compact orbit, $P_b\lesssim0.5\,{\rm yr}$. Here for the first time we propose and investigate the possibility of probing the spin of Sgr A* with two or more pulsars that are in orbits with larger orbital periods, $P_b\sim 2- 5\,{\rm yr}$, which represents a more realistic situation from population estimates. We develop a novel method for directly determining the spin of Sgr A* from the timing observables of two pulsars and it can be readily extended for combining more pulsars. With extensive mock data simulations, we show that combining a second pulsar improves the spin measurement by $2-3$ orders of magnitude in some situations, which is comparable to timing a pulsar in a very tight orbit.

astro-ph.HE↗

arXiv2024

Neutron stars in the bumblebee theory of gravity

Recently, theoretical studies on the bumblebee gravity model, a nonminimally-coupled vector-tensor theory that violates the Lorentz symmetry, have flourished, with a simultaneous increase in the utilization of observations to impose constraints. The static spherical solutions of neutron stars (NSs) in the bumblebee theory are calculated comprehensively in this work. These solutions with different coupling constants reveal a rich theoretical landscape for NSs, including vectorized NSs and NSs with finite radii but divergent masses. With these solutions, preliminary constraints on the asymptotic vector field values are obtained through restrictions on the stellar radius.

gr-qc↗

arXiv2024

Novel standard candle: Collapsing axion stars

The Hubble constant, $H_0$, is a crucial parameter in cosmology. However, various cosmic observations have produced differing posterior values for $H_0$, resulting in what is referred to as the $H_0$ tension. To resolve this discrepancy, utilizing other cosmological probes to constrain $H_0$ is advantageous. In the quest to identify dark matter candidates, the QCD axion and axionlike particles, collectively referred to as axions, have become leading contenders. These elusive particles can coalesce into dense structures known as axion stars via Bose-Einstein condensation. When these axion stars exceed a critical mass, typically through accretion or merging, they experience a self-induced collapse. This process results in short radio bursts, assuming a decay constant $f_a\lesssim10^{13}{\rm{GeV}}$, with the frequency depending on the axion mass and the luminosity determined by both the axion mass and decay constant. Therefore, we propose that collapsing axion stars could serve as a novel standard candle to constrain $H_0$. Even more interesting is that the radio bursts emitted by collapsing axion stars with specific parameters match the characteristics of observed non-repeating fast radio bursts (FRBs). Thus, FRBs generated by collapsing axion stars have the potential to be used as standard candles to constrain $H_0$.

hep-ph↗

arXiv2024

Vetting quark-star models with gravitational waves in the hierarchical Bayesian framework

The recent discovery of gravitational waves (GWs) has opened a new avenue for investigating the equation of state (EOS) of dense matter in compact stars, which is an outstanding problem in astronomy and nuclear physics. In the future, next-generation (XG) GW detectors will be constructed, deemed to provide a large number of high-precision observations. We investigate the potential of constraining the EOS of quark stars (QSs) with high-precision measurements of mass $m$ and tidal deformability $Λ$ from the XG GW observatories. We adopt the widely-used bag model for QSs, consisting of four microscopic parameters: the effective bag constant $B_{\rm eff}$, the perturbative quantum chromodynamics correction parameter $a_4$, the strange quark mass $m_s$, and the pairing energy gap $Δ$. With the help of hierarchical Bayesian inference, for the first time we are able to infer the EOS of QSs combining multiple GW observations. Using the top 25 loudest GW events in our simulation, we find that, the constraints on $B_{\rm eff}$ and $Δ$ are tightened by several times, while $a_4$ and $m_s$ are still poorly constrained. We also study a simplified 2-dimensional (2-d) EOS model which was recently proposed in literature. The 2-d model is found to exhibit significant parameter-estimation biases as more GW events are analyzed, while the predicted $m$-$Λ$ relation remains consistent with the full model.

astro-ph.HE↗

arXiv2024

Constraints on conformal ultralight dark matter couplings from the European Pulsar Timing Array

Millisecond pulsars are extremely precise celestial clocks: as they rotate, the beamed radio waves emitted along the axis of their magnetic field can be detected with radio telescopes, which allows for tracking subtle changes in the pulsars' rotation periods. A possible effect on the period of a pulsar is given by a potential coupling to dark matter, in cases where it is modeled with an "ultralight" scalar field. In this paper, we consider a universal conformal coupling of the dark matter scalar to gravity, which in turn mediates an effective coupling between pulsars and dark matter. If the dark matter scalar field is changing in time, as expected in the Milky Way, this effective coupling produces a periodic modulation of the pulsar rotational frequency. By studying the time series of observed radio pulses collected by the European Pulsar Timing Array experiment, we present constraints on the coupling of dark matter, improving on existing bounds. These bounds can also be regarded as constraints on the parameters of scalar-tensor theories of the Fierz-Jordan-Brans-Dicke and Damour-Esposito-Farèse types in the presence of a (light) mass potential term.

astro-ph.HE↗

arXiv2024

Unveiling the existence of nontensorial gravitational-wave polarizations from individual supermassive black hole binaries with pulsar timing arrays

With the strong evidence for a gravitational wave (GW) background in the nanohertz frequency band from pulsar timing arrays, the detection of continuous GWs from individual supermassive black hole binaries is already at the dawn. Utilizing continuous GWs to test theories of gravity, especially to test the polarizations of GWs is becoming more and more realistic. In this theoretical study, assuming a detection of signals from individual supermassive binary black holes, we use the null stream to estimate the capability of identifying the nontensorial polarizations of GWs. We consider cases for the nontensorial polarizations where the dipole radiation and quadrupole radiation dominate separately. With a frequentist method, we estimate the threshold of the nontensor-to-tensor relative amplitude above which extra polarizations can be detected. We also conduct Bayesian analysis to estimate parameters with the null stream data. Our treatment provides a data-analysis methodology using the null stream to probe the nontensorial GW polarizations with pulsar timing arrays.

gr-qc↗

arXiv2024

Effects from Dark Matter Halos on X-ray Pulsar Pulse Profiles

Neutron stars (NSs) can capture dark matter (DM) particles because of their deep gravitational potential and high density. The accumulated DM can affect the properties of NSs. In this work we use a general relativistic two-fluid formalism to solve the structure of DM-admixed NSs (DANSs) and the surrounding spacetime. Specifically, we pay attention to the situation where those DANSs possess DM halos. Due to the gravitational effect of the DM halo, the pulse profile of an X-ray pulsar is changed. Our study finds a universal relation between the peak flux deviation of the pulse profile and $M_{\rm halo}/R_{\rm BM}$, which is the ratio of the DM halo mass, $M_{\rm halo}$, to the baryonic matter (BM) core radius, $R_{\rm BM}$. Our results show that, when $M_{\rm halo}/R_{\rm BM}=0.292$ and the DM particle mass $m_f = 0.3\,$GeV, the maximum deviation of the profile can be larger than 100$\%$, which has implication in X-ray pulsar observation.

astro-ph.HE↗