arXiv subjects

Lunhua Shang

Publications and source records attributed to Lunhua Shang.

7 recordsLinked to original sources

arXiv2025

Radio frequency interference identification using eigenvalue decomposition for multi-beam observations

With the installation of next-generation phased array feed (PAF) receivers on radio telescopes, there is an urgent need to develop effective and computationally efficient radio frequency interference (RFI) mitigation methods for large-scale surveys. Here we present a new RFI mitigation package, called mRAID (multi-beam RAdio frequency Interference Detector), which uses the eigenvalue decomposition algorithm to identify RFI in cross-correlation matrix (CCM) of data recorded by multiple beams. When applied to high time-resolution pulsar search data from the Five-hundred-meter Aperture Spherical Radio Telescope (FAST), mRAID demonstrates excellent performance in identifying RFI over short timescales, thereby enhancing the efficiency of pulsar and fast radio burst (FRB) searches. Since the computation of the CCM and the eigenvalue decomposition for each time sub-integration and frequency channel are independent, the process is fully parallelisable. As a result, mRAID offers a significant computational advantage over commonly used RFI detection methods.

astro-ph.IM↗

arXiv2025

FAST Observations of the Microstructure in Interpulse Pulsars

In this study, we investigate the microstructure properties of four pulsars (PSRs J0953+0755 (B0950+08), J0627+0706, J0826+2637 (B0823+26) and J1946+1805 (B1944+17)) using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), with particular emphasis on identifying microstructure within interpulse (IP). Through the application of autocorrelation function (ACF) analysis and fast Fourier transform (FFT) techniques, we have systematically examined the periodicity of microstructure in these pulsars. Our findings represent the first successful detection of microstructure within IP. Furthermore, we conducted a comprehensive statistical analysis comparing the characteristic timescales ($τ_μ$) and the characteristic periods $P_μ$ of quasi-periodic microstructure between the main pulse (MP) and IP, and our results indicate that the $τ_μ$ and $P_μ$ of microstructure across components appear consistent within measurement errors for PSR J0627+0706, but microstructure in IP are relatively smaller than those in MP for PSR J0953+0755. Furthermore, the relationship between $P_μ$ of microstructure and the rotation period in neutron star populations was reconfirmed: $P_μ(\text{ms})=(1.337\pm0.114)\times P(\text{s})^{(1.063\pm0.038)}$.

astro-ph.HE↗

arXiv2024

Deep Searches for Radio Pulsations and Bursts from Four Magnetar and a Magnetar-like pulsar with FAST

We report on radio observations of four magnetars SGR 0501+4516, Swift 1834.9-0846, 1E 1841-045, SGR 1900+14 and a magnetar-like pulsar PSR J1846-0258 with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) at 1250 MHz. Notably, PSR J1846-0258 was observed one month after its 2020 X-ray outburst. The data from these observations were searched for periodic emissions and single pulses. No radio emission was detected for any of our targets. After accounting for the effect of red noise, the non-detections yield stringent upper limits on the radio flux density, with $S_{1250} \leq 16.9\, μ$Jy for the four magnetars and the magnetar-like pulsar, along with constraints on single-pulse flux densities. Our deep radio observations suggest that these magnetars and the magnetar-like pulsar are indeed radio-quiet sources or unfavorably beamed. The resulting flux upper limits, along with previous findings, are discussed, highlighting the significance of further radio observations of radio-quiet magnetars and the high-B magnetar-like pulsar.

astro-ph.HE↗

arXiv2024

Radio Pulsar B0950$+$08: Radiation in Magnetosphere and Sparks above Surface

We observed the nearby 100$\%$-duty-cycle radio pulsar B0950+08 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We obtained the polarization profile for its entire rotation, which enabled us to investigate its magnetospheric radiation geometry and the polar cap sparking pattern. After we excluded part of the profile in which the linear polarization factor is low ($\lesssim 30 \%$) and potentially contaminated by position angle jumps, the rest of the polarization position angle swing fits a classical rotating vector model (RVM) well. The bestfit RVM indicates that the inclination angle, $α$, and the impact angle, $β$, of this pulsar, are 100.5$^{\circ}$ and $-$33.2$^{\circ}$, respectively, suggesting that the radio emission comes from two poles.We find that, in such RVM geometry, either the annular vacuum gap or the core vacuum gap model would require that the radio emissions come from a high-altitude magnetosphere with heights from $\sim 0.25~R_{\rm LC}$ to $\sim 0.56~R_{\rm LC}$, with $R_{\rm LC}$ being the light cylinder radius. Both the main and inter-pulses' sparking points are located away from the magnetic pole, which could be relevant to the physical conditions on the pulsar surface.

astro-ph.HE↗

arXiv2024

AXPs/SGRs: strange stars with crusts?

The emission of Anomalous X-ray Pulsars (AXPs) and Soft Gamma-Ray Repeaters (SGRs) is believed to be powered by the dissipation of their strong magnetic fields, which coined the name `magnetar'. By combining timing and energy observational results, the magnetar model can be easily appreciated. From a timing perspective, the magnetic field strengths of AXPs and SGRs, calculated assuming dipole radiation, are extremely strong. From an energy perspective, the X-ray/soft gamma-ray luminosities of AXPs and SGRs are larger than their rotational energy loss rates (i.e., $ L_{\rm X}>\dot E_{\rm rot}$). It is thus reasonable to assume that the high-energy radiation comes from magnetic energy decay, and the magnetar model has been extensively discussed (or accepted). However, we argue that: (1) calculating magnetic fields by assuming that rotational energy loss is dominated by dipole radiation (i.e., $\dot{E}_{\rm rot}\simeq\dot{E}_μ$)) may be controversial, and we suggest that the energies carried by outflowing particles should also be considered; and (2) the fact that X-ray luminosity is greater than the rotational energy loss rate does not necessarily mean that the emission energy comes from the magnetic field decaying, which requires further observational testing. Furthermore, some observational facts conflict with the `magnetar' model, such as observations of anti-magnetars, high magnetic field pulsars, and radio and X-ray observations of AXPs/SGRs. Therefore, we propose a crusted strange star model as an alternative, which can explain many more observational facts of AXPs/SGRs.

astro-ph.HE↗

arXiv2024

The Study of Mode Switching behavior of PSR J0614+2229 Using the Parkes Ultra-wideband Receiver Observations

In this paper, we presented a detailed single pulse and polarization study of PSR J0614+2229 based on the archived data observed on 2019 August 15 (MJD 58710) and September 12 (MJD 58738) using the Ultra-wideband Low-frequency Receiver on the Parkes radio telescope. The single-pulse sequences show that this pulsar switches between two emission states, in which the emission of state A occurs earlier than that of state B in pulse longitude. We found that the variation in relative brightness between the two states is related to time and both states follow a simple power law very well. Based on the phase-aligned multi-frequency profiles, we found that there is a significant difference in the distributions of spectral index across the emission regions of the two states. Furthermore, we obtained the emission height evolution for the two emission states and found that, at a fixed frequency, the emission height of state A is higher than that of state B. What is even more interesting is that the emission heights of both states A and B have not changed with frequency. Our results suggest that the mode switching of this pulsar is possibly caused by changes in the emission heights that alter the distributions of spectral index across the emission regions of states A and B resulting in the frequency-dependent behaviors, i.e., intensity and pulse width.

astro-ph.HE↗

arXiv2023

Investigating the multi-drifting behavior of subpulses in PSR J2007$+$0910 with the FAST

The multi-drifting subpulse behaviors in PSR J2007+0910 have been studied carefully with the high sensitivity observations of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) at 1250 MHz. We found that there are at least six different single emission modes in PSR J2007+0910 are observed, four of which show significant subpulse drifting behaviors (modes A, B, C, and D), and the remaining two (modes $E_1$ and $E_2$) show stationary subpulse structures. The subpulse drifting periods of modes A, B, C, and D are $P_{3, A} = 8.7 \pm 1.6 P$, $P_{3, B} = 15.8 \pm 1.2 P$, $P_{3, C} = 21.6 \pm 1.3 P$ and $P_{3, D} = 32.3 \pm 0.9 P$, respectively, where $P$ represents the pulse period of this pulsar. The subpulse separation is almost the same for all modes $P_2 = 6.01 \pm 0.18 ^\circ$. Deep analysis suggests that the appearance and significant changes in the drifting period of multi-drifting subpulse emission modes for a pulsar may originate from the aliasing effect. The observed non-drifting modes may be caused by the spark point move with a period ~P_2. Our statistical analysis shows that the drift mode of this pulsar almost always switches from slower to faster drifts in the mode change. The interesting subpulse emission phenomenon of PSR J2007+0910 provides a unique opportunity to understand the switching mechanism of multi-drift mode.

astro-ph.HE↗