arXiv subjects

Shi-jun Dang

Publications and source records attributed to Shi-jun Dang.

4 recordsLinked to original sources

arXiv2026

Interstellar Scintillation of Three Nearby Pulsars with FAST

Interstellar scintillation probes the properties of the ionized interstellar medium as well as the dynamical behavior of pulsars themselves. Using the Five-hundred-meter Aperture Spherical Radio Telescope, we obtained hour-long observations of PSRs~J0837+0610, J1136+1551, and J1239+2453. We detected a single scintillation arc in PSRs~J0837+0610 and J1239+2453, and identified three distinct arcs in PSR~J1136+1551. Our analysis reveals that the arc curvature scales with observing frequency as $\eta \propto \nu^{-2.0\pm0.6}$ for PSR J0837+0610, and as $\eta \propto \nu^{-1.9\pm0.6}$ for PSR J1239+2453. For PSR J1136+1551, the two clearest arcs exhibit scaling relations of $\eta \propto \nu^{-1.6\pm0.6}$ and $\eta \propto \nu^{-2.0\pm0.4}$, respectively. However, the frequency dependence of the third arc could not be constrained due to its low signal-to-noise ratio at higher frequencies. Moreover, the corresponding scattering screens are measured at distances ranging from 30 to 420 pc from Earth. However, long-term scintillation monitoring or VLBI observations are needed to reliably measure the scattering screen.

astro-ph.HE↗

arXiv2025

A Rare Millisecond Pulsar with Cross-Pole Emission: Single-Pulse Insights from PSR J1857+0943

Studies of subpulse variability in millisecond pulsars (MSPs) offer important constraints on their emission physics. Using the high sensitivity of FAST, we present the first identification of distinct single pulse fluctuation behaviour in PSR J1857+0943. We find that the third component(MP\_C3) of the main pulse may originate from a different region than the other two main-pulse components and may instead share a common origin with the interpulse. This conclusion is supported by four observational evidence as follows: First, the LRCCF shows a clear anticorrelation between MP\_C3 and the interpulse. Second, the single-pulse polarization at the main-pulse longitude reveals obvious component mixing. Third, the modulation period of the interpulse components is roughly twice that of MP\_C3. Fourth, the reduced modulation index in MP\_C3 suggests possible mixing of emission from different regions. The interpretation in this letter contrasts with the usual assumption that the main pulse and interpulse originate from opposite magnetic poles. Hence, PSR J1857+0943 provides a rare laboratory for probing component-dependent plasma behaviour in an MSP magnetosphere. Our results offer direct evidence that the main pulse can include emission associated with more than one magnetic pole and highlight the importance of single-pulse diagnostics for understanding the geometry and dynamics of pulsars with interpulse emission. In addition, we analyse the jitter properties of this pulsar and measure a one-hour jitter of $\sigma_{J,1\rm h} = 78 \pm 3~\mathrm{ns}$ at 1.25 GHz, consistent with previous studies.

astro-ph.HE↗

arXiv2025

Results of 15-Year Pulsar Timing of PSR J0007+7303 with Fermi-LAT

The study of pulsar glitches provides a unique window into the internal structure and dynamic processes of neutron stars. PSR J0007+7303, a very bright gamma-ray pulsar, is the first pulsar discovered by the Fermi-LAT telescope. In this paper, we present the 15 years of timing results of this pulsar using the Fermi-LAT data. We identified nine glitches, five of which are newly discovered. Among these, two are small glitches, occurring between the three previously reported ones, while the other four are large glitches. The glitches exhibit fractional frequency changes ranging from 15 x 10^-9 to 1238 x 10^-9, with intervals of approximately 1-2 years between events. Uniquely, this pulsar shows no exponential recovery behavior following any glitch, setting it apart from most glitching pulsars. Furthermore, no significant changes were observed in the gamma-ray pulse profile, flux, or phase-averaged spectra before and after glitches, indicating the stability of the pulsar's emission properties despite internal changes. A parametric analysis of the glitches yielded a fractional moment of inertia of the crustal superfluid involved in glitches as 1.06 percent, which matches extremely well with previous statistical work if the non-dissipative entrainment effect is not considered and strongly supports the internal origin of these glitches. These results highlight the distinct glitch behavior of PSR J0007+7303 and offer valuable insights into the crust-superfluid interaction in neutron stars. The physical origin of no exponential recovery is also discussed.

astro-ph.HE↗

arXiv2025

Single-pulse-based interstellar scintillation studies of RRATs

The nature of irregularly spaced pulses of rotating radio transients (RRATs) complicates interstellar scintillation studies. In this letter, we report the primary scintillation parameters of a sample of RRATs using pairwise correlations of pulse spectra. Moreover, from the measured scintillation velocities, we constrain their transverse velocities. We also find a reduced modulation index, $\rm{m=0.13\pm0.01}$, for RRAT~J1538+2345. Several possible explanations are discussed. Furthermore, the single-pulse-based interstellar scintillation technique is applicable to other pulsar populations, including nulling pulsars and those with short scintillation timescales, and fast radio bursts.

astro-ph.HE↗