Shuang-Qiang Wang

Single-pulse studies of millisecond pulsars provide an important way to probe the plasma processes responsible for their radio emission, but such studies remain rare because of the weak emission and short rotation periods of these objects. Using the high sensitivity of the Five-hundred-meter Aperture Spherical Radio Telescope (FAST), we investigate the pulse-to-pulse variability of PSR J1857+0943 and report the first detection of distinct fluctuation behavior across its main pulse and interpulse. The integrated main pulse and interpulse each show multiple emission components with markedly different variability properties. Pulse longitude–resolved fluctuation analysis reveals quasiperiodic intensity modulation in both pulse regions, with the interpulse showing a characteristic modulation timescale approximately twice that observed in the trailing part of the main pulse. A longitude-resolved cross-correlation analysis further reveals a weak anticorrelation between the trailing main pulse emission and the interpulse at a lag of one rotation period, suggesting that these widely separated pulse longitude ranges may be influenced by a common magnetospheric process. The polarization properties of the single pulses in the same longitude range also differ from those of the adjacent main pulse components, supporting the presence of component-dependent emission behavior. In addition, we measure a 1 hr jitter noise of σ _J,1h = 73.2 ± 1.5 ns at 1.25 GHz, consistent with previous measurements. These results demonstrate that PSR J1857+0943 exhibits complex single-pulse variability and provide new observational constraints on the magnetospheric structure of interpulse millisecond pulsars.

We present phase-connected timing solutions, total-intensity and polarized profiles for two newly discovered pulsars, PSRs J1929+4105 and J2359+4239, identified by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in the Commensal Radio Astronomy FAST Survey (or CRAFTS). PSR J1929+4105 has a spin period of 41.59 ms and is in a 63 days orbit with an eccentricity of 0.00042. PSR J2359+4239, with a spin period of 60.53 ms, is in a 4 days orbit with an eccentricity of 0.0003. Since no post-Keplerian parameters have been measured for either system, we can only constrain the companion masses based on the mass function. The minimum companion masses for PSRs J1929+4105 and J2359+4239 are 0.72 M _⊙ and 0.467 M _⊙ , respectively. Given the small eccentricities of these systems, which rule out the possibility of double neutron star systems, we propose that both systems consist of a pulsar and a massive white dwarf companion. Simulations of the formation processes for these two systems were conducted using the rapid binary population synthesis code COMPAS. We estimated their distances using the NE2001 and YMW16 electron-density models, thereby contributing new data to the Galactic electron-density distribution. Motivated by the numerous discoveries of millisecond pulsar binaries by FAST, we further studied their height distribution in the Galaxy.

Rotating radio transients (RRATs) represent a critical yet enigmatic population of neutron stars whose sporadic emission is driven by highly intermittent magnetospheric states. We present a high-sensitivity, multi-epoch polarimetric study of RRAT J2237+2828 using the Five-hundred-meter Aperture Spherical radio Telescope, uncovering a complex, nonstationary magnetospheric environment. Individual bursts exhibit high linear polarization (20%–60%) and frequent orthogonal polarization modes, suggesting a fundamental coherent emission mechanism similar to canonical pulsars. However, the emission clearly shows bimodal behavior: pulses cluster into a High-energy burst state (Mode B) and a low-energy recovery state (Mode A). We identify a profound temporal asymmetry in the state-switching dynamics. While the transition from Mode B to Mode A occurs abruptly within 1–2 pulsar periods, the transition back to Mode B requires an extensive waiting time spanning hundreds to thousands of seconds. A compelling positive correlation between the inter-burst waiting time and the subsequent burst fluence ( r _s ≈ 0.45), coupled with a significant deviation from Poissonian statistics, strongly suggests that the system is regulated by an energy accumulation and release process. This long-term “system memory” and the observed timescales suggest that the intermittency is regulated by processes beyond pure magnetospheric dynamics, such as crustal stress accumulation or the evolution of multipolar magnetic fields. The stability of the rotation measure over 2 yr disfavors environmental origins and supports an intrinsic origin for the observed intermittency.

Pulsar timing is used for a variety of applications including tests of fundamental physics, probing the structure of neutron stars, and detecting nanohertz gravitational waves. Development of robust methods and generation of high-quality timing data is therefore of utmost importance. In this paper, we present a new technique for creating high-fidelity templates that can be used to measure the pulse times of arrival with significantly increased precision compared to existing methods. Our framework makes use of all available polarimetric information to generate frequency-dependent models of pulse-shape evolution of all four Stokes parameters. We apply this method to millisecond pulsars observed by the Parkes Pulsar Timing Array and show that it results in timing measurement uncertainties reduced up to $\sim$20–30 per cent. We also present, for the first time, phase- and frequency-resolved polarimetric measurements of millisecond pulsars observed with the Parkes Murriyang ultra-wide-bandwdith low receiver. The data, plots, and codes underlying this analysis are made publicly available.

We perform searches for gravitational-wave memory in the data of two major Pulsar Timing Array (PTA) experiments located in Europe and Australia. Supermassive black hole binaries (SMBHBs) are the primary sources of gravitational waves in PTA experiments. We develop and carry out the first search for late inspirals and mergers of these sources based on full numerical relativity waveforms with null (nonlinear) gravitational-wave memory. Additionally, we search for generic bursts of null gravitational-wave memory, exploring the possibilities of reducing the computational costs of these searches through kernel density estimation and normalizing flow approximations of the posteriors. We rule out mergers of SMBHBs with a chirp mass of 10 ¹⁰ M _⊙ up to 700 Mpc over 18 yr of observation at 95% credibility. We rule out the observation of generic displacement memory bursts with strain amplitudes >10 ⁻¹⁴ in brief periods of observation time but across the sky, or over the whole observation time but for certain preferred sky positions, at 95% credibility.

We perform searches for gravitational wave memory in the data of two major Pulsar Timing Array (PTA) experiments located in Europe and Australia. Supermassive black hole binaries (SMBHBs) are the primary sources of gravitational waves in PTA experiments. We develop and carry out the first search for late inspirals and mergers of these sources based on full numerical relativity waveforms with null (nonlinear) gravitational wave memory. Additionally, we search for generic bursts of null gravitational wave memory, exploring possibilities of reducing the computational cost of these searches through kernel density and normalizing flow approximation of the posteriors. We rule out the mergers of SMBHBs with a chirp mass of 10^10 Solar Mass up to 700 Mpc over 18 years of observation at 95% credibility. We rule out the observation of generic displacement memory bursts with strain amplitudes > 10^-14 in brief periods of the observation time but across the sky, or over the whole observation time but for certain preferred sky positions, at 95%$credibility.

蜘蛛脉冲星是一类特殊的毫秒脉冲星，其射电辐射通常因伴星物质遮挡而出现掩食现象。这类源的观测研究对于理解毫秒脉冲星的演化及高精度测时具有重要意义。本文使用中国五百米口径球面射电望远镜（FAST）对蜘蛛脉冲星 PSR J2055+3829 开展观测研究，发现其在掩食过程中存在显著的脉冲散射现象，最大散射时标达0.4毫秒。此外，通过噪声分析发现，在短时标下，该源的测时噪声由抖动噪声主导。