arXiv subjects

N. Wang

Publications and source records attributed to N. Wang.

At least 37 records · Page 2Linked to original sources

arXiv2024

Characterizing the Gamma-ray Emission Properties of the Globular Cluster M5 with the Fermi-LAT

We analyzed the globular cluster M5 (NGC 5904) using 15 years of gamma-ray data from the Fermi Large Area Telescope (LAT). Using rotation ephemerides generated from Arecibo and FAST radio telescope observations, we searched for gamma-ray pulsations from the seven millisecond pulsars (MSPs) identified in M5. We detected no significant pulsations from any of the individual pulsars. Also, we searched for possible variations of the gamma-ray emission as a function of orbital phase for all the six MSPs in binary systems, but did not detect any significant modulations. The gamma-ray emission from the direction of M5 is well described by an exponentially cutoff power-law spectral model, although other models cannot be excluded. The phase-averaged emission is consistent with being steady on a time scale of a few months. We estimate the number of MSPs in M5 to be between 1 and 10, using the gamma-ray conversion efficiencies for well-characterized gamma-ray MSPs in the Third Fermi Large Area Telescope Catalog of Gamma-ray Pulsars, suggesting that the sample of known MSPs in M5 is (nearly) complete, even if it is not currently possible to rule out a diffuse component of the observed gamma rays from the cluster.

astro-ph.HE↗

arXiv2024

Investigation of profile shifting and subpulse movement in PSR J0344-0901 with FAST

We report two phenomena detected in PSR J0344$-$0901 from two observations conducted at frequency centered at 1.25 GHz using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The first phenomenon manifests as shifting in the pulse emission to later longitudinal phases and then gradually returns to its original location. The event lasts for about 216 pulse periods, with an average shift of about $0.7^\circ$ measured at the peak of the integrated profile. Changes in the polarization position angle (PPA) are detected around the trailing edge of the profile, together with an increase in the profile width. The second phenomenon is characterized by the apparent movement of subpulses, which results in different subpulse track patterns across the profile window. For the first time in this pulsar, we identify four emission modes, each with unique subpulse movement, and determine the pattern periods for three of the emission modes. Pulse nulling was not detected. Modeling of the changes in the PPA using the rotating vector model gives an inclination angle of $75.12^\circ \pm 3.80^\circ$ and an impact parameter of $-3.17^\circ \pm 5.32^\circ$ for this pulsar. We speculate that the subpulse movement may be related to the shifting of the pulse emission.

astro-ph.HE↗

arXiv2024

Modelling The Radial Distribution of Pulsars in the Galaxy

The Parkes 20 cm Multibeam pulsar surveys have discovered nearly half of the known pulsars and revealed many distant pulsars with high dispersion measures. Using a sample of 1,301 pulsars from these surveys, we have explored the spatial distribution and birth rate of normal pulsars. The pulsar distances used to calculate the pulsar surface density are estimated from the YMW16 electron-density model. When estimating the impact of the Galactic background radiation on our survey, we projected pulsars in the Galaxy onto the Galactic plane, assuming that the flux density distribution of pulsars is uniform in all directions, and utilized the most up-to-date background temperature map. We also used an up-to-date version of the ATNF Pulsar Catalogue to model the distribution of pulsar flux densities at 1400 MHz. We derive an improved radial distribution for the pulsar surface density projected on to the Galactic plane, which has a maximum value at $\sim$4 kpc from the Galactic Centre. We also derive the local surface density and birthrate of pulsars, obtaining 47 $\pm$ 5 $\mathrm{kpc^{-2}}$ and $\sim$ 4.7 $\pm$ 0.5 $\mathrm{kpc^{-2}\ Myr^{-1}}$, respectively. For the total number of potentially detectable pulsars in the Galaxy, we obtain (1.1 $\pm$ 0.2) $\times$ $10^{4}$ and (1.1 $\pm$ 0.2) $\times$ $10^{5}$ before and after applying the TM98 beaming correction model. The radial distribution function is used to estimate the proportion of pulsars in each spiral arm and the Galactic centre.

astro-ph.HE↗

arXiv2024

Pulse Jitter and Single-pulse Variability in Millisecond Pulsars

Understanding the jitter noise resulting from single-pulse phase and shape variations is important for the detection of gravitational waves using pulsar timing array. We presented measurements of jitter noise and single-pulse variability of 12 millisecond pulsars that are part of the International Pulsar Timing Array sample using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We found that the levels of jitter noise can vary dramatically among pulsars. A moderate correlation with a correlation coefficient of 0.57 between jitter noise and pulse width is detected. To mitigate jitter noise, we performed matrix template matching using all four Stokes parameters. Our results revealed a reduction in jitter noise ranging from 6.7\% to 39.6\%. By performing longitude-resolved fluctuation spectrum analysis, we identified periodic intensity modulations in 10 pulsars. In PSR J0030+0451, we detected single-pulses with energies more than 10 times the average pulse energy, suggesting the presence of giant pulses. We also observed a periodic mode-changing phenomenon in PSR J0030+0451. We examined the achievable timing precision by selecting a sub-set of pulses with a specific range of peak intensity, but no significant improvement in timing precision is achievable.

astro-ph.HE↗

arXiv2023

Discovery of four pulsars in a pilot survey at intermediate Galactic latitudes with FAST

We present the discovery and timing results of four pulsars discovered in a pilot survey at intermediate Galactic latitudes with the Five-hundred Aperture Spherical Telescope (FAST). Among these pulsars, two belong to the category of millisecond pulsars (MSPs) with spin periods of less than 20 ms. The other two fall under the classification of "mildly recycled" pulsars, with massive white dwarfs as companions. Remarkably, this small survey, covering an area of 4.7 $deg^2$ , led to the discovery of four recycled pulsars. Such success underscores the immense potential of future surveys at intermediate Galactic latitudes. In order to assess the potential yield of MSPs, we conducted population simulations and found that both FAST and Parkes new phased array feed surveys, focusing on intermediate Galactic latitudes, have the capacity to uncover several hundred new MSPs.

astro-ph.HE↗

arXiv2023

Wide Bandwidth Observations of PSR J0941$-$39 and PSR J1107$-$5907

We present a polarization analysis of PSR J0941$-$39 and PSR J1107$-$5907, which exhibit transitions between being pulsars and rotating radio transients (RRATs), using the ultra-wide bandwidth low-frequency (UWL) receiver on Murriyang, the Parkes 64\,m radio telescope. The spectral index of each pulsar was measured, revealing distinct variations among different states. By using the rotating vector model (RVM), we determined that the magnetosphere geometry remains consistent between the RRAT state and the pulsar state for PSR J0941$-$39, with emissions originating from the same height in the magnetosphere. The occurrence of the RRAT state could be attributed to variations in currents within the pulsar's magnetosphere. Our results suggest that the emission mechanism of RRAT may share similarities with that of a typical pulsar.

astro-ph.HE↗

arXiv2023

Change of rotation measure during eclipse of a black widow PSR J2051$-$0827

Black widows are millisecond pulsars ablating their companions. The material blown from the companion blocks the radio emission, resulting in radio eclipses. The properties of the eclipse medium are poorly understood. Here, we present direct evidence of the existence of magnetic fields in the eclipse medium of the black widow PSR J2051$-$0827 using observations made with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We detect a regular decrease in rotation measure (RM) in the egress of eclipse, changing from $60\,\rm rad\,m^{-2}$ to $-28.7\,\rm rad\,m^{-2}$. The RM gradually changes back to normal when the line-of-sight moves away from the eclipse. The estimated line-of-sight magnetic field strength in the eclipse medium is $\sim 0.1$ G. The RM reversal could be caused by a change of the magnetic field strength along the line of sight due to binary orbital motion. The RM reversal phenomenon has also been observed in some repeating fast radio bursts (FRBs), and the study of spider pulsars may provide additional information about the origin of FRBs.

astro-ph.HE↗

arXiv2023

A burst storm from the repeating FRB 20200120E in an M81 globular cluster

The repeating fast radio burst (FRB) source FRB 20200120E is exceptional because of its proximity and association with a globular cluster. Here we report $60$ bursts detected with the Effelsberg telescope at 1.4 GHz. We observe large variations in the burst rate, and report the first FRB 20200120E `burst storm', where the source suddenly became active and 53 bursts (fluence $\geq 0.04$ Jy ms) occurred within only 40 minutes. We find no strict periodicity in the burst arrival times, nor any evidence for periodicity in the source's activity between observations. The burst storm shows a steep energy distribution (power-law index $α= 2.39\pm0.12$) and a bi-modal wait-time distribution, with log-normal means of 0.94$^{+0.07}_{-0.06}$ s and 23.61$^{+3.06}_{-2.71}$ s. We attribute these wait-time distribution peaks to a characteristic event timescale and pseudo-Poisson burst rate, respectively. The secondary wait-time peak at $\sim1$ s is $\sim50\times$ longer than the $\sim24$ ms timescale seen for both FRB 20121102A and FRB 20201124A -- potentially indicating a larger emission region, or slower burst propagation. FRB 20200120E shows order-of-magnitude lower burst durations and luminosities compared with FRB 20121102A and FRB 20201124A. Lastly, in contrast to FRB 20121102A, which has observed dispersion measure (DM) variations of $Δ{\rm DM} >1$ pc cm$^{-3}$ on month-to-year timescales, we determine that FRB 20200120E's DM has remained stable ($Δ{\rm DM} <0.15$ pc cm$^{-3}$) over $>10$ months. Overall, the observational characteristics of FRB 20200120E deviate quantitatively from other active repeaters, but it is unclear whether it is qualitatively a different type of source.

astro-ph.HE↗

arXiv2022

Individual pulse emission from the diffuse drifter PSR J1401$-$6357 using the ultrawideband receiver on the Parkes radio telescope

In this study, we report on a detailed single pulse analysis of the radio emission from the pulsar J1401$-$6357 (B1358$-$63) based on data observed with the ultrawideband low-frequency receiver on the Parkes radio telescope. In addition to a weak leading component, the integrated pulse profile features a single-humped structure with a slight asymmetry. The frequency evolution of the pulse profile is studied. Well-defined nulls, with an estimated nulling fraction greater than 2\%, are present across the whole frequency band. No emission is detected with significance above 3$σ$ in the average pulse profile integrated over all null pulses. Using fluctuation spectral analysis, we reveal the existence of temporal-dependent subpulse drifting in this pulsar for the first time. A clear double-peaked feature is present at exactly the alias border across the whole frequency band, which suggests that the apparent drift sense changes during the observation. Our observations provide further confirmation that the phenomena of pulse nulling and subpulse drifting are independent of observing frequency, which suggest that they invoke changes on the global magnetospheric scale.

astro-ph.HE↗

arXiv2022

A fast radio burst source at a complex magnetised site in a barred galaxy

Fast radio bursts (FRBs) are highly dispersed millisecond-duration radio bursts. Recent observations of a Galactic FRB suggest that at least some FRBs originate from magnetars, but the origin of cosmological FRBs is still not settled. Here we report the detection of 1863 bursts in 82 hr over 54 days from the repeating source FRB~20201124A. These observations show irregular short-time variation of the Faraday rotation measure (RM), which probes the density-weighted line-of-sight magnetic field strength, of individual bursts during the first 36 days, followed by a constant RM. We detected circular polarisation in more than half of the burst sample, including one burst reaching a high fractional circular polarisation of 75%. Oscillations in fractional linear and circular polarisations as well as polarisation angle as a function of wavelength were detected. All of these features provide evidence for a complicated, dynamically evolving, magnetised immediate environment within about an astronomical unit (au; Earth-Sun distance) of the source. Our optical observations of its Milky-Way-sized, metal-rich host galaxy reveal a barred spiral, with the FRB source residing in a low stellar density, interarm region at an intermediate galactocentric distance. This environment is inconsistent with a young magnetar engine formed during an extreme explosion of a massive star that resulted in a long gamma-ray burst or superluminous supernova.

astro-ph.HE↗

arXiv2022

Ultra-wide Bandwidth Observations of 19 pulsars with Parkes telescope

Flux densities are basic observation parameters to describe pulsars. In the most updated pulsar catalog, 24% of the listed radio pulsars have no flux density measurement at any frequency. Here, we report the first flux density measurements, spectral indices, pulse profiles, and correlations of the spectral index with pulsar parameters for 19 pulsars employing the Ultra-Wideband Low (UWL) receiver system installed on the Parkes radio telescope. The results for spectral indices of 17 pulsars are in the range between -0.6 and -3.10. The polarization profiles of thirteen pulsars are shown. There is a moderate correlation between the spectral index and spin frequency. For most pulsars detected, the S/N ratio of pulse profile is not high, so DM, Faraday rotation measure (RM), and polarization can not be determined precisely. Twenty-nine pulsars were not detected in our observations. We discuss the possible explanations for why these pulsars were not detected.

astro-ph.HE↗

arXiv2022

The discovery of a rotating radio transient J1918$-$0449 with intriguing emission properties with the five hundred meter aperture spherical radio telescope

In this study, we report on a detailed single pulse analysis of the radio emission from a rotating radio transient (RRAT) J1918$-$0449 which is the first RRAT discovered with the five hundred meter aperture spherical radio telescope (FAST). The sensitive observations were carried out on 30 April 2021 using the FAST with a central frequency of 1250 MHz and a short time resolution of 49.152 $μ$s, which forms a reliable basis to probe single pulse emission properties in detail. The source was successively observed for around 2 hours. A total of 83 dispersed bursts with significance above 6$σ$ are detected over 1.8 hours. The source's DM and rotational period are determined to be 116.1$\pm$0.4 \pcm \ and 2479.21$\pm$0.03 ms, respectively. The share of registered pulses from the total number of observed period is 3.12\%. No underlying emission is detected in the averaged off pulse profile. For bursts with fluence larger than 10 Jy ms, the pulse energy follows a power-law distribution with an index of $-3.1\pm0.4$, suggesting the existence of bright pulse emission. We find that the distribution of time between subsequent pulses is consistent with a stationary Poisson process and find no evidence of clustering over the 1.8 h observations, giving a mean burst rate of one burst every 66 s. Close inspection of the detected bright pulses reveals that 21 pulses exhibit well-defined quasi-periodicities. The subpulse drifting is present in non-successive rotations with periodicity of $2.51\pm0.06$ periods. Finally, possible physical mechanisms are discussed.

astro-ph.HE↗

arXiv2022

Arecibo and FAST Timing Follow-up of twelve Millisecond Pulsars Discovered in Commensal Radio Astronomy FAST Survey

We report the phase-connected timing ephemeris, polarization pulse profiles, Faraday rotation measurements, and Rotating-Vector-Model (RVM) fitting results of twelve millisecond pulsars (MSPs) discovered with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in the Commensal radio Astronomy FAST survey (CRAFTS). The timing campaigns were carried out with FAST and Arecibo over three years. Eleven of the twelve pulsars are in neutron star - white dwarf binary systems, with orbital periods between 2.4 and 100 d. Ten of them have spin periods, companion masses, and orbital eccentricities that are consistent with the theoretical expectations for MSP - Helium white dwarf (He WD) systems. The last binary pulsar (PSR J1912$-$0952) has a significantly smaller spin frequency and a smaller companion mass, the latter could be caused by a low orbital inclination for the system. Its orbital period of 29 days is well within the range of orbital periods where some MSP - He WD systems have shown anomalous eccentricities, however, the eccentricity of PSR J1912$-$0952 is typical of what one finds for the remaining MSP - He WD systems.

astro-ph.HE↗

arXiv2022

Emission Variation of a Long-period Pulsar Discovered by the Five-hundred-meter Aperture Spherical Radio Telescope (FAST)

We report on the variation in the single-pulse emission from PSR J1900+4221 (CRAFTS 19C10) observed at frequency centered at 1.25 GHz using the Five-hundred-meter Aperture Spherical radio Telescope. The integrated pulse profile shows two distinct components, referred to here as the leading and trailing components, with the latter component also containing a third weak component. The single-pulse sequence reveals different emissions demonstrating as nulling, regular, and bright pulses, each with a particular abundance and duration distribution. There also exists pulses that follow a log-normal distribution suggesting the possibility of another emission, in which the pulsar is radiating weakly. Changes in the profile shape are seen across different emissions. We examine the emission variations in the leading and trailing components collectively and separately, and find moderate correlation between the two components. The inclination angle is estimated to be about 7° based on pulse-width, and we discuss that nulling in this pulsar does not seem to show correlation with age and rotation period.

hep-th↗

arXiv2022

The Multiple Images of the Plasma Lensing FRB

We investigate the formation of multiple images as the radio signals from fast radio bursts (FRBs) pass through the plane of a plasma clump. The exponential model for the plasma clump is adopted to analyze the properties of the multiple images. By comparing with the classical dispersion relations, we find that one image has exhibited specific inverse properties to others, such as their delay times at high frequency is higher than that at low frequency, owing to the lensing effects of the plasma clump. We demonstrate that these inverse effects should be observable in some repeating FRBs. Our results predict deviation in the estimated DM across multiple images, consistent with the observations of FRB 121102 and FRB 180916.J0158+65. If other plasma lenses have effects similar to an exponential lens, we find that they should also give rise to the similar dispersion relation in the multiple images. For some repeating FRBs, analysis of the differences in time delay and in DM between multiple images at different frequencies can serve as a method to reveal the plasma distribution.

astro-ph.HE↗

arXiv2022

Detection of strong scattering close to the eclipse region of PSR B1957+20

We present the first measurement of pulse scattering close to the eclipse region of PSR B1957+20, which is in a compact binary system with a low-mass star. We measured pulse scattering time-scales up to 0.2 ms close to the eclipse and showed that it scales with the dispersion measure (DM) excess roughly as $τ\proptoΔ{\rm DM}^{2}$. Our observations provide the first evidence of strong scattering due to multi-path propagation effects in the eclipsing material. We show that Kolmogorov turbulence in the eclipsing material with an inner scale of $\sim100$ m and an outer scale of the size of the eclipse region can naturally explain the observation. Our results show that the eclipsing material in such systems can be highly turbulent and suggest that scattering is one of the main eclipsing mechanisms at around 1.4 GHz.

astro-ph.HE↗

arXiv2021

Analysis of a Tau Neutrino Origin for the Near-Horizon Air Shower Events Observed by the Fourth Flight of the Antarctic Impulsive Transient Antenna (ANITA)

We study in detail the sensitivity of the Antarctic Impulsive Transient Antenna (ANITA) to possible $ν_τ$ point source fluxes detected via $τ$-lepton-induced air showers. This investigation is framed around the observation of four upward-going extensive air shower events very close to the horizon seen in ANITA-IV. We find that these four upgoing events are not observationally inconsistent with $τ$-induced EASs from Earth-skimming $ν_τ$, both in their spectral properties as well as in their observed locations on the sky. These four events, as well as the overall diffuse and point source exposure to Earth-skimming $ν_τ$, are also compared against published ultrahigh-energy neutrino limits from the Pierre Auger Observatory. While none of these four events occurred at sky locations simultaneously visible by Auger, the implied fluence necessary for ANITA to observe these events is in strong tension with limits set by Auger across a wide range of energies and is additionally in tension with ANITA's Askaryan in-ice neutrino channel above $10^{19}$ eV. We conclude by discussing some of the technical challenges with simulating and analyzing these near horizon events and the potential for future observatories to observe similar events.

astro-ph.HE↗

arXiv2021

Unusual Emission Variations Near the Eclipse of A Black Widow PSR J1720$-$0533

We report on an {unusually} bright observation of PSR J1720$-$0533 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The pulsar is in a black widow system that {was discovered by the Commensal Radio Astronomy FAST Survey (CRAFTS). By coincidence, a bright scintillation maximum was simultaneous with the eclipse in our observation which allowed for precise measurements of flux density variations, as well as dispersion measure (DM) and polarization.} We found that there are quasi-periodic pulse emission variations with a modulation period of $\sim$ {22\,s} during the ingress of the eclipse, which could be caused by plasma lensing. {No such periodic modulation was found during the egress of the eclipse. } {The linear polarization of the pulsar disappears before the eclipse, even before there is a visually obvious change in DM. We also found that the pulse scattering maybe play an important role in the eclipse of PSR J1720$-$0533.}

astro-ph.HE↗