arXiv subjects

H. G. Wang

Publications and source records attributed to H. G. Wang.

At least 19 recordsLinked to original sources

arXiv2026

Relativistic effects of PSR~J1856--0039 double neutron star system in a 2.36-hour compact orbit

Compact double neutron star (DNS) systems are unique laboratories for testing gravitational theories and studying DNS mergers. Here we report the properties of a new DNS system, PSR J1856--0039, discovered in the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The pulsar is mildly recycled with a period of 23.4~ms in a compact eccentric orbit ($e=0.106$) with an orbital period of 2.36 hours. By following up FAST observations, we measured the relativistic effects, including the orbital period derivative $\dot{P}_{\rm orb}=-1.284\pm0.019\times10^{-12}$ s s$^{-1}$, periastron advance $\dotω=17.5859\pm0.0007$ deg yr$^{-1}$, and Einstein delay $γ=0.445\pm0.011$ ms. This DNS system has a low orbital inclination of $i=133^\circ.2\pm1^\circ.1$ and the lowest total mass of any known DNS, $M_{\rm tot}=2.48841\pm0.00015 M\odot$, with a determined pulsar mass of $1.304\pm0.022 M_\odot$ and a companion mass of $1.185\pm0.022 M_\odot$, one of the lowest neutron-star masses. The observed orbital decay due to gravitational-wave emission $\dot{P}^{\rm GW}_{\rm orb,obs}$ and the orbital decay predicted by general relativity $\dot{P}^{\rm GW}_{\rm orb,pred}$ are consistent at a level of $\dot{P}^{\rm GW}_{\rm orb,obs}/\dot{P}^{\rm GW}_{\rm orb,pred}=$1.009(14) (68% confidence). This DNS will merge after 82 Myr and may form a stable neutron star or collapse into a black hole after spin-down. Long-term monitoring could potentially probe the Lense-Thirring precession.

astro-ph.HE↗

arXiv2025

Pulsar radio emission height as a function of phase

We present an analytical treatment of the pulsar radio emission height as a function of phase based on a set of simplifying assumptions. Assuming a dipole field geometry, the emission height can be expressed as a function of phase and the impact angle. We found that: (1) The emission height is a quadratic function of the phase, given the magnetospheric geometry. The emission height is higher at the edge of the pulse profile than at the center. (2) The emission height is also a quadratic function of the impact angle. This point can be compared directly with the observations of the geodetic precessing pulsar PSR J1906+0746. (3) Larger inclination angle may imply a higher emission height, when other parameters are similar. (4) By assuming curvature radiation, or inverse Compton scattering, the Lorentz factor of the radio emitting particles can be obtained as a function of phase.

astro-ph.HE↗

arXiv2025

A pulsar-helium star compact binary system formed by common envelope evolution

A stellar common envelope occurs in a binary system when the atmosphere of an evolving star expands to encompass an orbiting companion object. Such systems are predicted to evolve rapidly, ejecting the stellar envelope and leaving the companion in a tighter orbit around a stripped star. We used radio timing to identify a pulsar, PSR J1928+1815, with a spin period of 10.55 ms in a compact binary system with an orbital period of 3.60 hours. The companion star has 1.0 to 1.6 solar masses, eclipses the pulsar for about 17% of the orbit, and is undetected at other wavelengths, so it is most likely a stripped helium star. We interpret this system as having recently undergone a common envelope phase, producing a compact binary.

astro-ph.HE↗

arXiv2025

The FAST Galactic Plane Pulsar Snapshot survey: VIII. 116 binary pulsars

Finding pulsars in binaries are important for measurements of the masses of neutron stars, for tests of gravity theories, and for studies of star evolution. We are carrying out the Galactic Plane Pulsar Snapshot survey (GPPS) by using the the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Here we present the Keplerian parameters for 116 newly discovered pulsars in the FAST GPPS survey, and obtain timing solutions for 29 pulsars. Companions of these pulsars are He white dwarfs, CO/ONe white dwarfs, neutron stars, main sequence stars and ultra light objects or even planets. Our observations uncover eclipses of 8 binary systems. The optical counterpart for the companion of PSR J1908+1036 is identified. The Post-Keplerian parameter $\dotω$ for the double neutron star systems PSR J0528+3529 and J1844-0128 have been measured, with which the total masses of the binary systems are determined.

astro-ph.HE↗

arXiv2025

The FAST Galactic Plane Pulsar Snapshot Survey: VII. Six millisecond pulsars in compact orbits with massive white dwarf companions

Binary millisecond pulsars with a massive white dwarf (WD) companion are intermediate-mass binary pulsars (IMBPs). They are formed via the Case BB Roche-lobe overflow evolution channel if they are in compact orbits with an orbital period of less than 1 day. They are fairly rare in the known pulsar population; only five such IMBPs have been discovered before, and one of them is in a globular cluster. Here we report six IMBPs in compact orbits: PSRs J0416+5201, J0520+3722, J1919+1341, J1943+2210, J1947+2304 and J2023+2853, discovered during the Galactic Plane Pulsar Snapshot survey by using the Five-hundred-meter Aperture Spherical radio Telescope, doubling the number of such IMBPs due to the high survey sensitivity in the short survey time of 5 minutes. Follow-up timing observations show that they all have either a CO WD or an ONeMg WD companion with a mass greater than about 0.8~$M_\odot$ in a very circular orbit with an eccentricity in the order of $\lesssim10^{-5}$. PSR J0416+5201 should be an ONeMg WD companion with a remarkable minimum mass of 1.28 $M_\odot$. These massive WD companions lead to a detectable Shapiro delay for PSRs J0416+5201, J0520+3722, J1943+2210, and J2023 +2853, indicating that their orbits are highly inclined. From the measurement of the Shapiro delay, the pulsar mass of J1943+2210 was constrained to be 1.84$^{\,+0.11}_{-0.09}$~$M_\odot$, and that of PSR J2023+2853 to be 1.28$^{\,+0.06}_{-0.05}$~$M_\odot$.

astro-ph.HE↗

arXiv2025

The FAST Galactic Plane Pulsar Snapshot survey: VI. The discovery of 473 new pulsars

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the most sensitive telescope at the $L$-band (1.0-1.5 GHz) and has been used to carry out the FAST Galactic Plane Pulsar Snapshot (GPPS) survey in the last 5 yr. Up to now, the survey has covered one-fourth of the planned areas within $\pm10^{\circ}$ from the Galactic plane visible by FAST, and discovered 751 pulsars. After the first publication of the discovery of 201 pulsars and one rotating radio transient (RRAT) in 2021 and 76 RRATs in 2023, here we report the discovery of 473 new pulsars from the FAST GPPS survey, including 137 new millisecond pulsars and 30 new RRATs. We find 34 millisecond pulsars discovered by the GPPS survey which can be timed with a precision better than 3 $μ$s by using FAST 15 minute observations and can be used for pulsar timing arrays. The GPPS survey has discovered eight pulsars with periods greater than 10 s including one with 29.77 s. The integrated profiles of pulsars and individual pulses of RRATs are presented. During the FAST GPPS survey, we also detected previously known pulsars and updated parameters for 52 pulsars. In addition, we discovered two fast radio bursts plus one probable case with high dispersion measures indicating their extragalactic origin.

astro-ph.HE↗

arXiv2024

The FAST Galactic Plane Pulsar Snapshot Survey -- V. PSR J1901+0658 in a double neutron star system

Double neutron star (DNS) systems offer excellent opportunities to test gravity theories. We report the timing results of PSR J1901+0658, the first pulsar discovered in the FAST Galactic Plane Pulsar Snapshot (GPPS) Survey. Based on timing observations by FAST over 5 yr, we obtain the phase-coherent timing solutions and derive the precise measurements of its position, spin parameters, orbital parameters, and dispersion measure. It has a period of 75.7 ms, a period derivative of 2.169(6)$\times 10^{-19}$ s s$^{-1}$, and a characteristic age of 5.5 Gyr. This pulsar is in an orbit with a period of 14.45 d and an eccentricity of 0.366. One post-Keplerian parameter, periastron advance, has been well-measured as being 0.00531(9) deg yr$^{-1}$, from which the total mass of this system is derived to be 2.79(7) M$_{\odot}$. The pulsar has the mass upper limit of 1.68 M$_{\odot}$, so the lower limit for the companion mass is 1.11 M$_{\odot}$. Because PSR J1901+0658 is a partially recycled pulsar in an eccentric binary orbit with such a large companion mass, it should be in a DNS system according to the evolution history of the binary system.

astro-ph.HE↗

arXiv2023

Rotating vector model and radius-to-frequency mapping in the presence of multipole magnetic field

The rotating vector model and radius-to-frequency mapping in the presence of multipole magnetic field in pulsars and magnetars are considered. An axisymmetric potential field is assumed. It is found that: (1) The radiation beam in the case of multipole field is wider than the dipole case. This may account the increasing pulse width at higher frequency of pulsars (anti-radius-to-frequency mapping). (2) The expression for the polarization position angle is unchanged. Only the inclination angle α and phase constant ϕ_0 will change. The angle between the rotational axis and line of sight, and the position angle constant ψ_0 will not change. When fitting the varying position angle of magnetars, these constraints should be considered. The appearance and disappearance of multipole field may account for the changing slope of position angle in the radio emitting magnetar Swift J1818.0-1607. Similar but more active process in magnetar magnetospheres may account for the diverse position angle in fast radius bursts.

astro-ph.HE↗

arXiv2023

The FAST Galactic Plane Pulsar Snapshot Survey: III. Timing results of 30 FAST-GPPS discovered pulsars

Timing observations are crucial for determining the basic parameters of newly discovered pulsars. Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) with the L-band 19-beam receiver covering the frequency range of 1.0--1.5 GHz, the FAST Galactic Plane Pulsar Snapshot (GPPS) Survey has discovered more than 600 faint pulsars with flux densities of only a few or a few tens of $μ$Jy at 1.25 GHz. To obtain accurate position, spin parameters and dispersion measure of a pulsar, and to calculate derived parameters such as the characteristic age and surface magnetic field, we collect available FAST pulsar data obtained either through targeted follow-up observations or through coincidental survey observations with one of the 19 beams of the receiver. From these data we obtain time of arrival (TOA) measurements for 30 newly discovered pulsars as well as for 13 known pulsars. We demonstrate that the TOA measurements acquired by the FAST from any beams of the receiver in any observation mode (e.g. the tracking mode or the snapshot mode) can be combined to get timing solutions. We update the ephemerides of 13 previously known pulsars and obtain the first phase-coherent timing results for 30 isolated pulsars discovered in the FAST GPPS Survey. Notably, PSR J1904+0853 is an isolated millisecond pulsar, PSR J1906+0757 is a disrupted recycled pulsar, and PSR J1856+0211 has a long period of 9.89 s that can constrain pulsar death lines. Based on these timing solutions, all available FAST data have been added together to obtain the best pulse profiles for these pulsars.

astro-ph.HE↗

arXiv2023

The FAST Galactic Plane Pulsar Snapshot survey: IV. Discovery of five fast radio bursts

We report five new fast radio bursts (FRBs) discovered from the Galactic Plane Pulsar Snapshot (GPPS) survey by the Five-hundred-meter Aperture Spherical radio Telescope (FAST): FRB\,20210126, FRB\,20210208, FRB\,20210705, FRB\,20211005 and FRB\,20220306. To date, no repeating bursts from these FRB sources have been detected in the follow-up monitoring observations, leading to their classification as potential one-off events. We obtain the basic parameters for these bursts, including position, dispersion measure (DM), pulse width, spectral index, scattering time-scale, etc. The fluences and flux densities are generally lower in comparison to the values observed in one-off bursts discovered by other telescopes. Among the observed bursts, polarization data for 4 bursts were recorded during observations. Consequently, we obtain polarization profiles and Faraday rotation measures (RMs) for these bursts.

astro-ph.HE↗

arXiv2023

Investigation into the reflection properties of the neutron star low-mass X-ray binary 4U 1636-53

We present the spectroscopy of the neutron star low-mass X-ray binary 4U 1636-53 using six simultaneous XMM-Newton and Rossi X-ray Timing Explorer observations. We applied different self-consistent reflection models to explore the features when the disk is illuminated by either the corona or the neutron star surface. We found that the spectra could be well fitted by these two types of models, with the derived emissivity index below a typical value of 3. The relative low emissivity can be explained if the neutron star and the corona, working together as an extended illuminator, simultaneously illuminate and ionize the disk. Additionally, the derived ionization parameter in the lamppost geometry is larger than the theoretical prediction. This inconsistency likely suggests that the corona does not emit isotropically in a realistic context. Furthermore, we also found that there is a possible trend between the height of the corona and the normalization of the disk emission. This could be understood either as a variation in the reflected radiation pressure or in the context of a jet base. Finally, we found that the disk is less ionized if it is illuminated by the neutron star, indicating that the illuminating source has significant influence on the physical properties of the disk.

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

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

Circular polarization of fast radio bursts in the curvature radiation scenario

The curvature radiation is applied to the explain the circular polarization of FRBs. Significant circular polarization is reported in both apparently non-repeating and repeating FRBs. Curvature radiation can produce significant circular polarization at the wing of the radiation beam. In the curvature radiation scenario, in order to see significant circular polarization in FRBs (1) more energetic bursts, (2) burst with electrons having higher Lorentz factor, (3) a slowly rotating neutron star at the centre are required. Different rotational period of the central neutron star may explain why some FRBs have high circular polarization, while others don't. Considering possible difference in refractive index for the parallel and perpendicular component of electric field, the position angle may change rapidly over the narrow pulse window of the radiation beam. The position angle swing in FRBs may also be explained by this non-geometric origin, besides that of the rotating vector model.

astro-ph.HE↗

arXiv2021

Three aspects of the radius-to-frequency mapping in fast radio bursts

We further explored the radius-to-frequency mapping in cases of FRBs. An analytical treatment of Lyutikov (2020) is presented. The frequency dependence of the drifting rate and the drifting timescale are obtained. The aberration effect and the twist of the magnetic field lines may result in drifting in both directions. For one FRB, the burst width is larger at lower frequency according to the radius-to-frequency mapping. For the FRB population, the magnetic fields of the repeaters may be larger than that of the non-repeaters. Then, according to the radius-to-frequency mapping, the burst widths of the repeaters will be wider than that of the apparent non-repeaters. If similar window function (or emission cones) like that of pulsars and magnetars is also at work in the case of FRBs, then the window function may explain the single or multiple components of FRB profiles. The radius-to-frequency mapping modeling is to some degree independent of the underlying radio emission mechanism.

astro-ph.HE↗

arXiv2021

A broadband radio study of PSR J0250+5854: the slowest-spinning radio pulsar known

We present radio observations of the most slowly rotating known radio pulsar PSR J0250+5854. With a 23.5 s period, it is close, or even beyond, the $P$-$\dot{P}$ diagram region thought to be occupied by active pulsars. The simultaneous observations with FAST, the Chilbolton and Effelsberg LOFAR international stations, and NenuFAR represent a five-fold increase in the spectral coverage of this object, with the detections at 1250 MHz (FAST) and 57 MHz (NenuFAR) being the highest- and lowest-frequency published respectively to date. We measure a flux density of $4\pm2$ $μ$Jy at 1250 MHz and an exceptionally steep spectral index of $-3.5^{+0.2}_{-1.5}$, with a turnover below $\sim$95 MHz. In conjunction with observations of this pulsar with the GBT and the LOFAR Core, we show that the intrinsic profile width increases drastically towards higher frequencies, contrary to the predictions of conventional radius-to-frequency mapping. We examine polarimetric data from FAST and the LOFAR Core and conclude that its polar cap radio emission is produced at an absolute height of several hundreds of kilometres around 1.5 GHz, similar to other rotation-powered pulsars across the population. Its beam is significantly underfilled at lower frequencies, or it narrows because of the disappearance of conal outriders. Finally, the results for PSR J0250+5854 and other slowly spinning rotation-powered pulsars are contrasted with the radio-detected magnetars. We conclude that magnetars have intrinsically wider radio beams than the slow rotation-powered pulsars, and that consequently the latter's lower beaming fraction is what makes objects such as PSR J0250+5854 so scarce.

astro-ph.HE↗

arXiv2021

The FAST Galactic Plane Pulsar Snapshot survey: I. Project design and pulsar discoveries

Discovery of pulsars is one of the main goals for large radio telescopes. The Five-hundred-meter Aperture Spherical radio Telescope (FAST), that incorporates an L-band 19-beam receiver with a system temperature of about 20~K, is the most sensitive radio telescope utilized for discovering pulsars. We designed the {\it snapshot} observation mode for a FAST key science project, the Galactic Plane Pulsar Snapshot (GPPS) survey, in which every four nearby pointings can observe {\it a cover} of a sky patch of 0.1575 square degrees through beam-switching of the L-band 19-beam receiver. The integration time for each pointing is 300 seconds so that the GPPS observations for a cover can be made in 21 minutes. The goal of the GPPS survey is to discover pulsars within the Galactic latitude of $\pm10^{\circ}$ from the Galactic plane, and the highest priority is given to the inner Galaxy within $\pm5^{\circ}$. Up to now, the GPPS survey has discovered 201 pulsars, including currently the faintest pulsars which cannot be detected by other telescopes, pulsars with extremely high dispersion measures (DMs) which challenge the currently widely used models for the Galactic electron density distribution, pulsars coincident with supernova remnants, 40 millisecond pulsars, 16 binary pulsars, some nulling and mode-changing pulsars and rotating radio transients (RRATs). The follow-up observations for confirmation of new pulsars have polarization-signals recorded for polarization profiles of the pulsars. Re-detection of previously known pulsars in the survey data also leads to significant improvements in parameters for 64 pulsars. The GPPS survey discoveries are published and will be updated at http://zmtt.bao.ac.cn/GPPS/ .

astro-ph.HE↗

arXiv2021

Rotating vector model for magnetars

The modification of the rotating vector model in the case of magnetars are calculated. Magnetars may have twisted magnetic field compared with normal pulsars. The polarization position angle of magnetars will change in the case of a twisted magnetic field. For a twisted dipole field, we found that the position angle will change both vertically and horizontally. During the untwisting process of the magnetar magnetosphere, the modifications of the position angle will evolve with time monotonously. This may explain the evolution of the position angle in magnetar PSR J1622-4950 and XTE J1810-197. The relation between the emission point and the line of sight will also change. We suggest every magnetospheric models of magnetars also calculate the corresponding changes of position angle in their models. Order of magnitude estimation formula for doing this is given. This opens the possibility to extract the magnetic field geometry of magnetars from their radio polarization observations.

astro-ph.HE↗