arXiv subjects

C. Wang

Publications and source records attributed to C. Wang.

At least 37 records · Page 2Linked to original sources

arXiv2025

Universality classes of Anderson localization transitions in disordered three-dimensional non-Hermitian systems with exceptional points

We conduct a numerical study of wave localization in disordered three-dimensional non-Hermitian systems featuring exceptional points. The energy spectrum of a disordered non-Hermitian Hamiltonian, exhibiting both parity-time and parity-particle-hole symmetries, forms a cross in the complex energy plane, with an exceptional point fixed at the origin. Near the exceptional point, the system experiences a disorder-driven quantum phase transition from extended to localized states, characterized as an Anderson localization transition in non-Hermitian systems. Notably, we identify a universal critical exponent that remains independent of the distribution of random variables. The model also supports Anderson localization transitions away from the exceptional points, albeit with different critical exponents. Furthermore, we investigate wave localization in a non-Hermitian system lacking parity-time symmetry, revealing distinct universality classes. By comparing the obtained critical exponents with those reported in the literature, we conclude that the presence of exceptional points introduces new universality classes that extend beyond the established 38-fold symmetry classification for non-Hermitian systems.

cond-mat.dis-nn↗

arXiv2025

A high fraction of close massive binary stars at low metallicity

At high metallicity, a majority of massive stars have at least one close stellar companion. The evolution of such binaries is subject to strong interaction processes, heavily impacting the characteristics of their life-ending supernova and compact remnants. For the low-metallicity environments of high-redshift galaxies constraints on the multiplicity properties of massive stars over the separation range leading to binary interaction are crucially missing. Here we show that the presence of massive stars in close binaries is ubiquitous, even at low metallicity. Using the Very Large Telescope, we obtained multi-epoch radial velocity measurements of a representative sample of 139 massive O-type stars across the Small Magellanic Cloud, which has a metal content of about one fifth of the solar value. We find that 45% of them show radial velocity variations which demonstrate that they are members of close binary systems, and predominantly have orbital periods shorter than one year. Correcting for observational biases indicates that at least 70[+11:-6]% of the O stars in our sample are in close binaries, and that at least 68[+7:-8]% of all O stars interact with a companion star during their lifetime. We found no evidence supporting a statistically significant trend of the multiplicity properties with metallicity. Our results indicate that multiplicity and binary interactions govern the evolution of massive stars and determine their cosmic feedback and explosive fates.

astro-ph.SR↗

arXiv2025

GRB 241105A: A test case for GRB classification and rapid r-process nucleosynthesis channels

Gamma-ray bursts (GRBs) offer a powerful window to probe the progenitor systems responsible for the formation of heavy elements through the rapid neutron capture (r-) process, thanks to their exceptional luminosity, which allows them to be observed across vast cosmic distances. GRB 241105A, observed at a redshift of z = 2.681, features a short initial spike (1.5 s) and a prolonged weak emission lasting about 64 s, positioning it as a candidate for a compact binary merger and potentially marking it as the most distant merger-driven GRB observed to date. However, the emerging ambiguity in GRB classification necessitates further investigation into the burst's true nature. Prompt emission analyses, such as hardness ratio, spectral lag, and minimum variability timescales, yield mixed classifications, while machine learning-based clustering places GRB 241105A near both long-duration mergers and collapsar GRBs. We conducted observations using the James Webb Space Telescope (JWST) to search for a potential supernova counterpart. Although no conclusive evidence was found for a supernova, the host galaxy's properties derived from the JWST observations suggest active star formation with low metallicity, and a sub-kpc offset of the afterglow from the host, which appears broadly consistent with a collapsar origin. Nevertheless, a compact binary merger origin cannot be ruled out, as the burst may plausibly arise from a fast progenitor channel. This would have important implications for heavy element enrichment in the early Universe.

astro-ph.HE↗

arXiv2025

Single-ion anisotropy driven chiral magnetic order in a spin-1 antiferromagnetic chain

Chirality in magnetic systems gives rise to a wide range of exotic phenomena, yet its influence in $S=1$ chains remains largely unexplored. Here, we present a comprehensive experimental study of a chiral antiferromagnetic (AFM) $S=1$ chain, [Ni(pym)(H$_{2}$O)$_{4}$]SO$_{4} \cdot$ H$_{2}$O (pym = pyrimidine), where the Ni(II) octahedral orientation exhibits a four-fold chiral periodicity. Muon spin rotation measurements indicate the onset of long-range magnetic order below $T_{\rm N} = 1.82(2)\,\mathrm{K}$. Neutron diffraction measurements reveal a chiral AFM order driven by a chiral modulation of the easy-axis anisotropy direction, rather than the typical scenario of Dzyaloshinskii-Moriya interactions, geometrical frustration or higher-order interactions. Inelastic neutron scattering (INS) measurements reveal dispersive spin-wave excitations well described by linear spin-wave theory, with Hamiltonian parameters $J_{0} = 6.81(1)\,\mathrm{K}$ (intrachain exchange), $J'_{1\rm a} = -0.091(1)\,\mathrm{K}$ (interchain exchange), and $D = -3.02(1)\,\mathrm{K}$ (easy-axis single-ion anisotropy). These parameters are further validated by Monte Carlo simulations of the magnetisation. Additionally, the INS data reveal multiple dispersionless bands, suggesting the presence of further excitations beyond the scope of our linear spin-wave theory.

cond-mat.str-el↗

arXiv2025

Transition of blue-core helicon discharge

This study explores the transitional characteristics of blue-core helicon discharge, which to our knowledge was not particularly focused on before. Parameters are measured on recently built advanced linear plasma device, i.e. Multiple Plasma Simulation Linear Device (MPS-LD) by various diagnostics including Langmuir probe, optical emission spectrometer, and standard high-speed camera. It is found that the jump direction of electron density (from low level to high level) is opposite to that of electron temperature (from high level to low level). Electron density increases significantly and the radial profile becomes localized near the axis when the blue-core transition occurs. With increased field strength, electron density increases whereas electron temperature drops. The radial profile of electron temperature looks like a ``W" shape, i.e. minimizing around the edge of blue-core column. Electron density increases with background pressure, while electron temperature peaks around certain pressure value. High-speed videos show that the plasma column oscillates radially and experiences azimuthal instabilities with high rate once entered blue-core mode. An electromagnetic solver (EMS) based on Maxwell's equations and a cold-plasma dielectric tensor is also employed to compute the wave field and power absorption during blue-core transition, to provide more details that are valuable for understanding the transitional physics but not yet available in experiment. The results show that wave field in both radial and axial directions changes significantly during the transition, its structure differs from antenna to downstream, and the power dependence of wave magnetic field is overall opposite to that of wave electric field. This work presents comprehensive characteristics of the transitional blue-core discharge and is important to both physics understanding and practical applications.

physics.plasm-ph↗

arXiv2025

Populations of evolved massive binary stars in the Small Magellanic Cloud I: Predictions from detailed evolution models

Context. The majority of massive stars are born with a close binary companion. How this affects their evolution and fate is still largely uncertain, especially at low metallicity. Aims. We derive synthetic populations of massive post-interaction binary products and compare them with corresponding observed populations in the Small Magellanic Cloud (SMC). Methods. We analyse 53298 detailed binary evolutionary models computed with MESA. Our models include the physics of rotation, mass and angular momentum transfer, magnetic internal angular momentum transport, and tidal spin-orbit coupling. They cover initial primary masses of 5-100Msun, initial mass ratios of 0.3-0.95, and all initial periods for which interaction is expected. They are evolved through the first mass transfer and the donor star death, a possible ensuing Be/X-ray binary phase, and they end when the mass gainer leaves the main sequence. Results.In our fiducial synthetic population, 8% of the OB stars in the SMC are post-mass transfer systems, and 7% are merger products. In many of our models, the mass gainers are spun up and form Oe/Be stars. While our model underpredicts the number of Be/X-ray binaries in the SMC, it reproduces the main features of their orbital period distribution and the observed number of SMC binary WR stars. We expect $\sim$50 OB+BH binaries below and $\sim$170 above 20d orbital period. The latter might produce merging double BHs. However, their progenitors, the predicted long-period WR+OB binaries, are not observed. Conclusions. While the comparison with the observed SMC stars supports many physics assumptions in our high-mass binary models, a better match of the large number of observed OBe stars and Be/X-ray binaries likely requires a lower merger rate and/or a higher mass transfer efficiency during the first mass transfer. The fate of the initially wide O star binaries remains uncertain.

astro-ph.SR↗

arXiv2025

A pulsar-helium star compact binary system formed by common envelope evolution

A stellar common envelope occurs in a binary system when the atmosphere of an evolving star expands to encompass an orbiting companion object. Such systems are predicted to evolve rapidly, ejecting the stellar envelope and leaving the companion in a tighter orbit around a stripped star. We used radio timing to identify a pulsar, PSR J1928+1815, with a spin period of 10.55 ms in a compact binary system with an orbital period of 3.60 hours. The companion star has 1.0 to 1.6 solar masses, eclipses the pulsar for about 17% of the orbit, and is undetected at other wavelengths, so it is most likely a stripped helium star. We interpret this system as having recently undergone a common envelope phase, producing a compact binary.

astro-ph.HE↗

arXiv2025

Training the Next Generation of Seismologists: Delivering Research-Grade Software Education for Cloud and HPC Computing through Diverse Training Modalities

With the rise of data volume and computing power, seismological research requires more advanced skills in data processing, numerical methods, and parallel computing. We present the experience of conducting training workshops over various forms of delivery to support the adoption of large-scale High-Performance Computing and Cloud computing to advance seismological research. The seismological foci were on earthquake source parameter estimation in catalogs, forward and adjoint wavefield simulations in 2 and 3 dimensions at local, regional, and global scales, earthquake dynamics, ambient noise seismology, and machine learning. This contribution describes the series of workshops that were delivered as part of research projects, the learning outcomes of the participants, and lessons learned by the instructors. Our curriculum was grounded on open and reproducible science, large-scale scientific computing and data mining, and computing infrastructure (access and usage) for HPC and the cloud. We also describe the types of teaching materials that have proven beneficial to the instruction and the sustainability of the program. We propose guidelines to deliver future workshops on these topics.

physics.geo-ph↗

arXiv2025

Investigating an Erupting Metric-decimetric Radio Depression and its Physical Origin

We present direct metric-decimetric radio imaging observations of a fascinating quiescent filament eruption on 2024 March 17 using data from the DAocheng Radio Telescope (DART), with a combination of the Solar Dynamics Observatory and the Chinese Ha Solar Explorer. At the radio band, even though the filament is difficult to identify in its early phase, it rapidly became distinct and formed a continuous loop-like dark structure during the eruption, i.e., so-called radio depression. Compared with the fragmentation of the erupting filament observed at the Ha and EUV bands, the radio depression appeared more coherently. Based on synthetic radio images from a three-dimensional magnetohydrodynamics (MHD) simulation of a flux-rope-filament eruption, it is suggested that the radio depression originates from the absorption of cold and dense materials within the erupting flux rope to the background emission. The absorption seems to be stronger than that at the Ha and EUV bands, thus leading to their apparent discrepancies. Moreover, the radio depression is also found to occupy the lower part but not the whole body of the flux rope.

astro-ph.SR↗

arXiv2025

Populations of evolved massive binary stars in the Small Magellanic Cloud II: Predictions from rapid binary evolution

Massive star evolution plays a crucial role in astrophysics but bares large uncertainties. This problem becomes more severe by the majority of massive stars being born in close binary systems, whose evolution is affected by the interaction of their components. We want to constrain major uncertainties in massive binary star evolution, in particular the efficiency and the stability of the first mass transfer phase. We use the rapid population synthesis code ComBinE to generate synthetic populations of post-interaction binaries, assuming constant mass-transfer efficiency. We employ a new merger criterion that adjusts self-consistently to any prescribed mass-transfer efficiency. We tailor our synthetic populations to be comparable to the expected binary populations in the Small Magellanic Cloud (SMC). We find that the observed populations of evolved massive binaries can not be reproduced with a single mass-transfer efficiency. Instead, a rather high efficiency (>50%) is needed to reproduce the number of Be stars and Be/X-ray binaries in the SMC, while a low efficiency (~10%) leads to a better agreement with the observed number of Wolf-Rayet stars. We construct a corresponding mass-dependent mass-transfer efficiency recipe to produce our fiducial synthetic SMC post-interaction binary population. It reproduces the observed number and properties of the Be/X-ray and WR-binaries rather well, and is not in stark disagreement with the observed OBe star population. It further predicts two large, yet unobserved populations of OB+BH binaries, that is ~100 OB+BH systems with rather small orbital periods (<20 days) and ~40 longer period OBe+BH systems.

astro-ph.SR↗

arXiv2025

New insight into the Rapid Burster by Insight-HXMT

We report the timing and spectral analyses upon of the type II X-ray bursts from the Rapid Burster (MXB 1730--335) observed by Insight-HXMT and Swift/XRT. By stacking the long-duration bursts, we find for the first time that the hard X-rays are lagging than the soft X-rays by 3 seconds. However, such a lag is not visible for the short-duration bursts, probably because of the poor statistics. For all bursts the energy spectrum is found to be non-thermal, thanks to the broad band coverage of Insight-HXMT. These findings put new insights into the type-II bursts and require a temporally showing-up corona for possible interpretation.

astro-ph.HE↗

arXiv2025

Floquet topological state induced by light-driven band inversion in SnTe

High intensity coherent light can dress matter, realizing new hybrid phases that are not accessible in equilibrium. This effect results from the coherent interaction between Bloch states inside the solid and the periodic field of impinging photons which produces hybrid light-matter states called Floquet-Bloch states that can alter properties of the solid. Optically inducing a topological state in a semiconductor using so-called Floquet engineering is an exciting prospect. However, it has not been realized, despite its theoretical prediction more than 10 years ago. Here we show that an ultrashort-lived topological state that is absent at equilibrium in the ground state of SnTe can be created with femtosecond light pulses. This occurs when the photoexcitation is similar in energy with the band gap of this polar semiconductor. We observe a concomitant renormalization of the band dispersions that reveals the generation of Floquet states connecting to the topological state. We therefore provide the first direct experimental observation of a Floquet topological state and propose that it is driven by a light-induced band inversion in SnTe. Our discovery opens the way for controlling optically on-demand the topological properties of semiconductors.

cond-mat.str-el↗

arXiv2025

The FAST Galactic Plane Pulsar Snapshot survey: VIII. 116 binary pulsars

Finding pulsars in binaries are important for measurements of the masses of neutron stars, for tests of gravity theories, and for studies of star evolution. We are carrying out the Galactic Plane Pulsar Snapshot survey (GPPS) by using the the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Here we present the Keplerian parameters for 116 newly discovered pulsars in the FAST GPPS survey, and obtain timing solutions for 29 pulsars. Companions of these pulsars are He white dwarfs, CO/ONe white dwarfs, neutron stars, main sequence stars and ultra light objects or even planets. Our observations uncover eclipses of 8 binary systems. The optical counterpart for the companion of PSR J1908+1036 is identified. The Post-Keplerian parameter $\dotω$ for the double neutron star systems PSR J0528+3529 and J1844-0128 have been measured, with which the total masses of the binary systems are determined.

astro-ph.HE↗

arXiv2025

Binarity at Low Metallicity (BLOeM) -- Multiplicity properties of Oe and Be stars

Rapidly rotating classical OBe stars have been proposed as the products of binary interactions, and the fraction of Be stars with compact companions implies that at least some are. However, to constrain the interaction physics spinning up the OBe stars, a large sample of homogeneously analysed OBe stars with well-determined binary characteristics and orbital parameters are required. We investigate the multiplicity properties of a sample of 18 Oe, 62 Be, and two Of?p stars observed within the BLOeM survey in the Small Magellanic Cloud. We analyse the first nine epochs of spectroscopic observations obtained over approximately three months in 2023. Radial velocities (RVs) of all stars are measured. Applying commonly-used binarity criteria we classify objects as binaries, binary candidates, and apparently single (RV stable) objects. We further inspect the spectra for double-lined spectroscopic binaries and cross-match with catalogues of X-ray sources and photometric binaries. We classify 14 OBe stars as binaries, and an additional 11 as binary candidates. The two Of?p stars are apparently single. Two more objects are most likely currently interacting binaries. Without those, the observed binary fraction for the OBe sample (78 stars) is f_OBe_obs=0.18+/-0.04 (f_obs_cand=0.32+/-0.05 including candidates). This fraction is less than half of that measured for OB stars in BLOeM. Combined with the lower fraction of SB2s, this suggests that OBe stars have indeed fundamentally different binary properties than OB stars. We find no evidence for OBe binaries with massive compact companions, in contrast to expectations from binary population synthesis. Our results support the binary scenario as an important formation channel for OBe stars, as post-interaction binaries may have been disrupted or the stripped companions of OBe stars are harder to detect.

astro-ph.SR↗

arXiv2025

Binarity at LOw Metallicity (BLOeM): The multiplicity properties and evolution of BAF-type supergiants

Given the uncertain evolutionary status of blue supergiant stars, their multiplicity properties hold vital clues to better understand their origin and evolution. As part of The Binarity at LOw Metallicity (BLOeM) campaign in the Small Magellanic Cloud we present a multi-epoch spectroscopic survey of 128 supergiant stars of spectral type B5--F5, which roughly correspond to initial masses in the range 6 to 30 solar masses. The observed binary fraction for the B5-9 supergiants is 25+/-6 % (10+/-4 %) and 5+/-2 % (0 %) for the A-F stars, using a radial velocity (RV) variability threshold of 5 kms (10 kms) as a criterion for binarity. Accounting for observational biases we find an intrinsic multiplicity fraction of less than 18% for the B5-9 stars and 8$^{+9}_{-7}$% for the AF stars, for the orbital periods up to 10$^{3.5}$day and mass-ratios (q) in the range 0.1 < q < 1. The large stellar radii of these supergiant stars prevent short orbital periods but we demonstrate that this effect alone cannot explain our results. We assess the spectra and RV time series of the detected binary systems and find that only a small fraction display convincing solutions. We conclude that the multiplicity fractions are compromised by intrinsic stellar variability such that the true multiplicity fraction may be significantly smaller. Our main conclusions from comparing the multiplicity properties of the B5-9 and AF supergiants to that of their less evolved counterparts is that such stars cannot be explained by a direct evolution from the main sequence. Furthermore, by comparing their multiplicity properties to red supergiant stars we conclude that the AF supergiant stars are neither progenitors nor descendants of red supergiants.

astro-ph.SR↗

arXiv2025

The FAST Galactic Plane Pulsar Snapshot Survey: VII. Six millisecond pulsars in compact orbits with massive white dwarf companions

Binary millisecond pulsars with a massive white dwarf (WD) companion are intermediate-mass binary pulsars (IMBPs). They are formed via the Case BB Roche-lobe overflow evolution channel if they are in compact orbits with an orbital period of less than 1 day. They are fairly rare in the known pulsar population; only five such IMBPs have been discovered before, and one of them is in a globular cluster. Here we report six IMBPs in compact orbits: PSRs J0416+5201, J0520+3722, J1919+1341, J1943+2210, J1947+2304 and J2023+2853, discovered during the Galactic Plane Pulsar Snapshot survey by using the Five-hundred-meter Aperture Spherical radio Telescope, doubling the number of such IMBPs due to the high survey sensitivity in the short survey time of 5 minutes. Follow-up timing observations show that they all have either a CO WD or an ONeMg WD companion with a mass greater than about 0.8~$M_\odot$ in a very circular orbit with an eccentricity in the order of $\lesssim10^{-5}$. PSR J0416+5201 should be an ONeMg WD companion with a remarkable minimum mass of 1.28 $M_\odot$. These massive WD companions lead to a detectable Shapiro delay for PSRs J0416+5201, J0520+3722, J1943+2210, and J2023 +2853, indicating that their orbits are highly inclined. From the measurement of the Shapiro delay, the pulsar mass of J1943+2210 was constrained to be 1.84$^{\,+0.11}_{-0.09}$~$M_\odot$, and that of PSR J2023+2853 to be 1.28$^{\,+0.06}_{-0.05}$~$M_\odot$.

astro-ph.HE↗

arXiv2025

The FAST Galactic Plane Pulsar Snapshot survey: VI. The discovery of 473 new pulsars

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the most sensitive telescope at the $L$-band (1.0-1.5 GHz) and has been used to carry out the FAST Galactic Plane Pulsar Snapshot (GPPS) survey in the last 5 yr. Up to now, the survey has covered one-fourth of the planned areas within $\pm10^{\circ}$ from the Galactic plane visible by FAST, and discovered 751 pulsars. After the first publication of the discovery of 201 pulsars and one rotating radio transient (RRAT) in 2021 and 76 RRATs in 2023, here we report the discovery of 473 new pulsars from the FAST GPPS survey, including 137 new millisecond pulsars and 30 new RRATs. We find 34 millisecond pulsars discovered by the GPPS survey which can be timed with a precision better than 3 $μ$s by using FAST 15 minute observations and can be used for pulsar timing arrays. The GPPS survey has discovered eight pulsars with periods greater than 10 s including one with 29.77 s. The integrated profiles of pulsars and individual pulses of RRATs are presented. During the FAST GPPS survey, we also detected previously known pulsars and updated parameters for 52 pulsars. In addition, we discovered two fast radio bursts plus one probable case with high dispersion measures indicating their extragalactic origin.

astro-ph.HE↗

arXiv2025

Field-orientation-dependent magnetic phases in GdRu$_2$Si$_2$ probed with muon-spin spectroscopy

Centrosymmetric GdRu$_2$Si$_2$ exhibits a variety of multi-Q magnetic states as a function of temperature and applied magnetic field, including a square skyrmion-lattice phase. The material's behavior is strongly dependent on the direction of the applied field, with different phase diagrams resulting for fields applied parallel or perpendicular to the crystallographic $c$ axis. Here, we present the results of muon-spin relaxation ($μ^+$SR) measurements on single crystals of GdRu$_2$Si$_2$. Our analysis is based on the computation of muon stopping sites and consideration of zero-point motion effects, allowing direct comparison with the underlying spin textures in the material. The muon site is confirmed experimentally, using angle-dependent measurements of the muon Knight shift. Using transverse-field $μ^+$SR with fields applied along either the [001] or [100] crystallographic directions, we distinguish between the magnetic phases in this system via their distinct muon response, providing additional evidence for the skyrmion and meron-lattice phases, while also suggesting the existence of RKKY-driven muon hyperfine coupling. Zero-field $μ^+$SR provides clear evidence for a transition between two distinct magnetically-ordered phases at 39 K.

cond-mat.str-el↗