Xinjiang Astronomical Observatory, Chinese Academy of Sciences

Li Z., Zhao X., Zhang W., Wang H.

ABSTRACTPulsars, characterized as highly magnetized and rapidly rotating neutron stars, offer a unique laboratory for probing physics under extreme conditions. Magnetars, a subclass of pulsars powered by magnetic field energy, exhibit quantized and highly degenerate Landau levels for relativistic electrons in their crustal ultrastrong magnetic fields. The energy difference between these Landau levels and the field‐free system determines the magnetic susceptibility. We first review spin degrees of freedom in relativistic electrons and magnetization mechanisms, then employ quantum statistical methods to calculate the magnetic susceptibility of relativistic electron gases in magnetar crusts. Finally, numerical simulations for the paramagnetic susceptibility oscillatory in superhigh magnetic fields in the magnetar crust was performed. Our results reveal that the magnetization under ultrastrong fields demonstrates oscillatory behavior analogous to the de Haas–van Alphen effect observed in certain low‐temperature metals. The total susceptibility, , comprises a non‐oscillatory component () and an oscillatory term (), where higher harmonic amplitudes of the oscillatory susceptibility grow with increasing electron density. Notably, the total paramagnetic susceptibility of electrons near the crust‐core boundary does not exceed the critical magnetization threshold. However, if an ultrastrong magnetic field exists in the neutron star core, the susceptibility of the electron gas could surpass this critical value, suggesting the potential occurrence of non‐equilibrium magnetization processes. This implies a first‐order phase transition, akin to gas–liquid transitions, leading to coexisting stable magnetization states or metastable supercooled magnetic phases. A sudden transition from metastable to stable states may release stored magnetic energy, offering a plausible explanation for the observed excess radiation during magnetar giant flares.

Xia Y., Wang J., Kuroyanagi S., Yan W., Wen Y., Kapur A., Zou J., Feng Y., Di Marco V., Mishra S., Russell C.J., Wang S., Zhao D., Zhu X.

Pulsar timing arrays (PTAs) are designed to detect nanohertz-frequency gravitational waves (GWs). Since GWs are anticipated from cosmic strings, PTAs offer a viable approach to testing their existence. We present the results of the first Bayesian search for gravitational-wave bursts from cosmic string cusps (GWCSs) using the third PPTA data release for 30 ms pulsars. In this data collection, we find no evidence for GWCS signals. We compare a model with a GWCS signal to one with only noise, including a common spatially uncorrelated red noise (CURN), and find that our data are more consistent with the noise-only model. We then establish upper limits on the strain amplitude of GWCSs at the pulsar term, based on the analysis of 30 ms pulsars, after finding no compelling evidence. We find the addition of a CURN with different spectral indices into the noise model has a negligible impact on the upper limits. And the upper limit range of the amplitude of the pulsar-term GWCSs is concentrated between 10−12 and 10−11. Finally, we set upper limits on the amplitude of GWCS events, parametrized by width and event epoch, for a single-pulsar PSR J1857 + 0943. Moreover, we derive the upper limit on the cosmic string tension as a function of burst width and compare it with previous results.

Wen Y., Wang J., Yan W., Yuan J., Wang N., Xia Y., Zou J.

The stable rotation of young pulsars is often interrupted by two non-deterministic phenomena: glitches and red timing noise, glitches, and red timing noise. Timing noise provides insights into plasma and nuclear physics under extreme conditions. The framework leverages rotational symmetry in pulsar spin-down models and temporal symmetry in noise processes to achieve computational efficiency, aligning with the journal’s focus on symmetry principles in physical systems. In this paper, we apply a novel frequentist framework developed within the PINT software package (v0.9.8) to analyze single-pulsar noise processes. Using 17.5 years of pulse time-of-arrival (TOA) data for the young pulsar PSR J1741−3016, observed with the Nanshan 26 m radio telescope, we investigate its timing properties. In this study, we employed the Downhill Weighted Least-Squares Fitter to estimate the pulsar’s spin parameters and position. The Akaike Information Criterion (AIC) was used for model parameter selection. The results obtained with PINT were compared to those from ENTERPRISE and TEMPONEST, two Bayesian-based frameworks. We demonstrate that PINT achieves comparable results with significantly reduced computational costs. Additionally, the adequacy of the noise model can be readily verified through visual inspection tools. Future research will utilize this framework to analyze timing noise across a large sample of young pulsars.

Deng C., Huang Y., Xu F., Kurban A.

Gamma-ray bursts (GRBs) are among the most luminous electromagnetic transients in the universe, providing unique insights into extreme astrophysical processes and serving as promising probes for cosmology. Unlike Type Ia supernovae, which have a unified explosion mechanism, GRBs cannot directly act as standard candles for tracing cosmic evolution at high redshifts due to significant uncertainties in their underlying physical origins. Empirical correlations derived from statistical analyses involving various GRB parameters provide valuable information regarding their intrinsic properties. In this brief review, we describe various correlations among GRB parameters involving the prompt and afterglow phases, discussing possible theoretical interpretations behind them. The scarcity of low-redshift GRBs poses a major obstacle to the application of GRB empirical correlations in cosmology, referred to as the circularity problem. We present various efforts aiming at calibrating GRBs to address this challenge and leveraging established empirical correlations to constrain cosmological parameters. The pivotal role of GRB sample quality in advancing cosmological research is underscored. Some correlations that could potentially be utilized as redshift indicators are also introduced.

Wang H., Zhu C., Lü G., Li L., Liu H., Guo S., Lu X.

Zhang Z., Ye Q., Wang N., Meng G.

As the observation frequency of large-aperture antennas increases, the requirements for measuring main reflector deformation have become more stringent. Recently, the rapid development of deep learning has led to its application in antenna deformation prediction. However, achieving high accuracy requires a large number of high-fidelity deformation samples, which is often challenging to obtain. To address these problems, this paper establishes a high-accuracy antenna surface deformation measurement model based on a multi-fidelity transfer learning neural network (MF-TLNN). Firstly, a low-fidelity surrogate model is constructed using a large number of simulation deformation samples to ensure its robustness. Secondly, the MF-TLNN structure is designed and trained using a small number of high-fidelity samples obtained from actual measurements of the main reflector deformation via out-of-focus (OOF) holography method. Thirdly, a Zernike correction module is utilized to provide additional constraints and ensure the stability of the results. Experimental results show that the proposed method can closely approximate radio holography measurements in terms of accuracy and is almost real-time in terms of speed.

Punanova A.F., Borshcheva K., Fedoseev G.S., Caselli P., Wiebe D.S., Vasyunin A.I.

ABSTRACT Formaldehyde is a key precursor in the formation routes of many complex organic molecules (COMs) in space. It is also an intermediate step in CO hydrogenation sequence that leads to methanol formation on the surface of interstellar grains in cold dense prestellar cores where pristine ices are formed. Various chemical models successfully reproduce the COMs abundances in cold cores, however, they consistently overpredict the abundance of formaldehyde by an order of magnitude. This results in an inverse H$_2$CO:CH$_3$OH abundance ratio obtained in the astrochemical simulations as compared to the observed values. In this work, we present a homogeneous data set of formaldehyde observational maps obtained towards seven dense cores in the L1495 filament with the IRAM 30-m telescope. Resolving the spatial distribution of the molecules is essential to test the chemical models. We carefully estimate the formaldehyde column densities and abundances to put reliable observational constraints on the chemical models of cold cores. Through numerous tests, we aim to constrain the updated chemical model monaco to better align with the observed formaldehyde abundance and its ratio to methanol. In particular, we elaborate on the branching ratio of the CH$_3$ + O reaction at low temperatures. The revised monaco model reproduces abundances of both methanol and formaldehyde within an order of magnitude. However, the model tends to overproduce formaldehyde and underproduce methanol. Consequently, the model systematically overestimates the H$_2$CO:CH$_3$OH ratio, although it remains within an order of magnitude of the values derived from observations.

Yuan W., Dai L., Feng H., Jin C., Jonker P., Kuulkers E., Liu Y., Nandra K., O’Brien P., Piro L., Rau A., Rea N., Sanders J., Tao L., Wang J., et. al.

Abstract The Einstein Probe (EP) is an interdisciplinary mission of time-domain and X-ray astronomy. Equipped with a wide-field lobster-eye X-ray focusing imager, EP will discover cosmic X-ray transients and monitor the X-ray variability of known sources in 0.5–4 keV, at a combination of detecting sensitivity and cadence that is not accessible to the previous and current wide-field monitoring missions. EP can perform quick characterisation of transients or outbursts with a Wolter-I X-ray telescope onboard. In this paper, the science objectives of the EP mission are presented. EP is expected to enlarge the sample of previously known or predicted but rare types of transients with a wide range of timescales. Among them, fast extragalactic transients will be surveyed systematically in soft X-rays, which include γ-ray bursts and their variants, supernova shock breakouts, and the predicted X-ray transients associated with binary neutron star mergers. EP will detect X-ray tidal disruption events and outbursts from active galactic nuclei, possibly at an early phase of the flares for some. EP will monitor the variability and outbursts of X-rays from white dwarfs, neutron stars and black holes in our and neighbouring galaxies at flux levels fainter than those detectable by the current instruments, and is expected to discover new objects. A large sample of stellar X-ray flares will also be detected and characterised. In the era of multi-messenger astronomy, EP has the potential of detecting the possible X-ray counterparts of gravitational wave events, neutrino sources, and ultra-high energy γ-ray and cosmic ray sources. EP is expected to help advance the studies of extreme objects and phenomena revealed in the dynamic X-ray universe, and their underlying physical processes. Besides EP’s strength in time-domain science, its follow-up telescope, with excellent performance, will also enable advances in many areas of X-ray astronomy.

Liu Y., Sun H., Xu D., Svinkin D.S., Delaunay J., Tanvir N.R., Gao H., Zhang C., Chen Y., Wu X.-., Zhang B., Yuan W., An J., Bruni G., Frederiks D.D., et. al.

Long gamma-ray bursts (GRBs) are believed to originate from core collapse of massive stars. High-redshift GRBs can probe the star formation and reionization history of the early Universe, but their detection remains rare. Here we report the detection of a GRB triggered in the 0.5–4 keV band by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated as EP240315a, whose bright peak was also detected by the Swift Burst Alert Telescope and Konus-Wind through off-line analyses. At a redshift of z = 4.859, EP240315a showed a much longer and more complicated light curve in the soft-X-ray band than in gamma rays. Benefiting from a large field of view (~3,600°2) and a high sensitivity, EP-WXT captured the earlier engine activation and extended late engine activity through a continuous detection. With a peak X-ray flux at the faint end of previously known high-z GRBs, the detection of EP240315a demonstrates the great potential for EP to study the early universe via GRBs. The death of massive stars has traditionally been discovered by explosive events in the gamma-ray band. Liu et al. show that the sensitive wide-field monitor on board Einstein Probe can reveal a weak soft-X-ray signal much earlier than gamma rays.

Liu P., Yuan J., Ge M., Ye W., Zhou S., Dang S., Zhou Z., Gügercinoğlu E., Tu Z.H., Wang P., Li A., Li D., Wang N.

ABSTRACT Pulsar glitch is a phenomenon characterized by abrupt changes in the spin period over less than a minute. We present a comprehensive analysis of glitches in four gamma-ray pulsars by combining the timing observation data from Fermi-Large Area Telescope (Fermi-LAT) and Parkes 64 m radio telescope. The timing data of five pulsars, namely PSRs J1028–5819, J1420–6048, J1509–5850, J1709–4429 (B1706–44), and J1718–3825, are examined over 14 yr of observations for each. A total of 12 glitches are identified in four pulsars, including a previously unreported glitch. That is, a new small glitch is identified for PSR J1718–3825 in MJD $\sim$ 59121(8), with a fractional glitch size of $\Delta \nu /\nu \sim 1.9(2) \times 10^{-9}$. For PSR J1420–6048, our investigation confirms the presence of two linear recovery terms during the evolution of $\dot{\nu }$ following glitches 4, 6, and 8. Moreover, an exponential recovery process was identified after glitch 8, with a recovery fraction (Q) of $Q = 0.0131(5)$ and a corresponding time-scale of $\tau _{\rm d} = 100(6)$ d. Regarding the fourth glitch of PSR J1709–4429, our analysis reveals the presence of two exponential recovery terms with degree of recovery and decay time-scales Q1 = 0.0104(5), $\tau _{\rm d1}=72(4)$ d, and Q2 = 0.006(1), $\tau _{\rm d2}=4.2(6)$ d, respectively. For the remaining previously reported glitches, we also refine the glitch epochs and recovery process through precise fitting of the timing data. We discuss how multiband data of glitches can help better characterize the glitch recoveries and constrain the underlying physics of glitch events. Our findings demonstrate that the accumulation of observational data reveals the rich complexity of the glitch phenomenon, aiding in the search for a well-established interpretation.

Li L., Li K., Gao X., Chen X., Feng S., Gao D., Guo D., Chen X., Gao X., Sun G., Bai S.Y., Esamdin A.

ABSTRACT This paper presents the photometric and spectroscopic analysis of a long-period totally eclipsing contact binary (HAT 307-0007476) for the first time. This system is a low mass ratio ($q\sim 0.114$) and medium contact binary ($f\sim 37.1~{{\ \rm per\ cent}}$). Two flare events were detected in multiple bands observations in December 2022. The interval between the two flare events is 4 d. The average duration of these two flares is about 2289 s. Both the two flares achieve the energy levels of superflares. The excess emission of the H$_\alpha$ line in the LAMOST spectra of this object was analysed, indicating its chromospheric activity. The O–C diagram showed a long-term orbital period increase, which is due to the mass transfer between the two component stars. We conclude that HAT 307-0007476 is currently in a stable region based on both Jspin/Jorb and the comparison between the instability parameters and its current values.

Zhang Y., Dong S., Wang J., Zhao S., Yuan H., Song H., Jiang M.

The study of time scale facilitates stable and reliable operation of time-keeping systems. Algos algorithm is a common method for calculating the time scale. Improving the stability of the time scale is an important issue in the research of time-keeping technology. In this paper, an optimization method of the clock difference data preprocessing in algorithm is proposed. We apply the theory of optimal weight to the calculation of time scale weight for improving the stability of the dynamic time scale. The proposed algorithm is called Improved Dynamic Algos-like (IDAlgos). We use the IDAlgos for joint experiments of cesium clocks ensemble, hydrogen masers ensemble, and hydrogen-cesium clocks ensemble, respectively. The results compared with Conventional Dynamic Algos-like (CDAlgos) show that i) for the case of cesium clocks ensemble, the short-term stability has been improved, the stability increased by 22.5% in 2 h and 20.8% in 4 h. ii) for the case of hydrogen masers ensemble, the stability increased by 18.3% in 1 h and 31.3% in 128 h, that is, both long-term and short-term stability has been improved. iii) for the clock ensemble combined of hydrogen masers and cesium clocks, the long-term and short-term stability has been greatly improved,among them, the stability increased by 64.6% in 1 h and 69.3% in 128 h. Consequently, the IDAlgos has obvious improving on the stability of the time scale

Di H., Shi H., Yi Z.

The anomalous orbits of trans-Neptunian objects can be accounted for by the planet 9 hypothesis. One intriguing possibility is that planet 9 could be a dilute axion star captured by the Solar System, with the ratio of the axion star to dark matter being approximately 1/10. Although dilute axion stars can emit monochromatic signals through two-photon decay, the spontaneous decay signal is too weak to be detected by radio telescopes. However, we find that stimulated decay of the dilute axion star, which explains planet 9, can occur by directing a radio beam with a power of 50 MW into the star. The resulting echo can be detected by terrestrial telescopes such as SKA, FAST, ngLOBO, and LOFAR. Therefore, the dilute axion star can be distinguished from other planet 9 candidates, such as a primordial black hole or a free-floating planet captured by the Solar System. Published by the American Physical Society 2025

Li J., Zhang X., Liu X.C.

Xu L., Lin X., Liu L., Wang J., Lin X., Bai C., Lin Z., Wang W., Yang Y., Cheng X., Li F.