Search

Observations of interplanetary scintillation (IPS) are an efficient remote-sensing method to study the solar wind and inner heliosphere. From 2016 to 2018, some distinctive observations of IPS sources like 3C 286 and 3C 279 were accomplished with the Five-hundred-meter Aperture Spherical radio Telescope (FAST), the largest single-dish telescope in the world. Due to the 270–1620 MHz wide frequency coverage of the ultra-wideband (UWB) receiver, one can use both single-frequency and dual-frequency analyses to determine the projected velocity of the solar wind. Moreover, based on the extraordinary sensitivity owing to the large collecting surface area of FAST, we can observe weak IPS signals. With the advantages of both the wider frequency coverage and high sensitivity, and also with our radio frequency interference (RFI) mitigation strategy and an optimized model-fitting method, in this paper we analyse the fitting confidence intervals of the solar wind velocity and present some preliminary results achieved using FAST, which point to the current FAST system being highly capable of carrying out observations of IPS.

Parallel tracks in the relation between the lower kilohertz quasi-periodic oscillation (kHz QPO) frequency ν1 and the X-ray intensity I have been observed in the neutron star low-mass X-ray binary (NS-LMXB) 4U 1728−34, and we try to ascribe these phenomena to the bimodal accretion modes, i.e. the disc accretion and radial accretion. For the source with one constant radial accretion rate $\dot{M}_{\rm r}$, as the increase of the disc accretion rate $\dot{M}_{\rm d}$, the NS magnetosphere-disc radius can shrink from ∼18 to ∼16 km, while ν1 increases from ∼670 to ∼870 Hz. Then, due to the increase of the kHz QPO frequency and total X-ray intensity Itot, the source will trace out an oblique track in ν1–I relation. While, if the source enters another constant radial accretion rate due to the variation of the accretion environment, the increase of the disc accretion rate can arise another parallel track in ν1–I relation. Finally, the reliability of the theoretical assumptions, the variability of the accretion radius and accretion rate, as well as the dependence of the two accretion modes, are also investigated and discussed.

The recently discovered very massive stellar black holes (BHs), i.e., the binary BH (BBH) merger for the gravitational-wave (GW) event GW190521 by LIGO-Virgo O3a with the component masses of ${85}_{\ensuremath{-}14}^{+21}\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ and ${66}_{\ensuremath{-}18}^{+17}\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$, have aroused much attention. Our statistical knowledge of the mass distributions of the BBHs observed in LIGO-Virgo GW detections is helpful to understanding the origin of GW190521. Hence, in order to determine whether GW190521 is consistent with the same population as the other LIGO-Virgo BBHs, we analyze the BBH total masses in the GWTC-2 catalog with the classical Gaussian mixture models (GMMs). Based on the model selection results in this analysis, we cannot confidently conclude that GW190521 is a new population of BBHs distinct from the other LIGO-Virgo BBHs due to the limitation of the current small sample size of GW-observed BBHs. Moreover, our results suggest that there is a clear preference for a two-component GMM for the sample of BBHs in GWTC-2 without GW190521, implying that two (or more) distinct underlying populations of these BBHs may exist because of the differing astrophysical origins. After a consideration for the detailed features of the above two-component GMM, we find statistical evidence that tends to support a mixture model for LIGO-Virgo BBH formation, which is in line with previous studies that also supported a multicomponent model (for example, one consisting of isolated binary evolution and dynamical channels).

A SET-state conductance change in a hafnium-oxide resistive switching memory cell due to repeated read events is investigated. We characterize a read-induced conductance change at different read voltages and SET-state conductance levels. Our result shows that the read-induced conductance degradation exhibits a two-stage evolution with the read pulse number. A SET-state conductance decreases slightly in the first stage and then follows inverse power-law dependence on the read number in the second stage. The power factor is an exponential function of a read voltage without regard to the SET-state conductance level, and the read pulse number at the transition of the two stages is related to a read voltage and conductance level. An analytical model to describe the two-stage conductance evolution is proposed. The parameters in the model are extracted from measurement data. Our model is verified by good agreement between the modeled and measured results in a wide range of read pulse number, read voltage, and SET-state conductance level.

With the discovery of the double neutron star (DNS) merger event GW170817 by LIGO, DNS systems have become one of the important candidates for gravitational wave (GW) observation. There are 19 DNS systems that have been discovered, and PSR J1906+0746 is the youngest DNS system with the age of about 0.1 Myrs. We simulate its orbital decay over its entire life by the GW radiation from the initial stage to the coalescence. For the DNS PSR J1906+0746, we obtain its initial orbital period of 3.99 hrs (3.98 hrs at present) with the nearly circular orbit, and the merger age of 3.18 × 108 yr. At the last minute of coalescence, corresponding to the orbital radius change from 335 to 30 km, we present the GW frequency to be 30 and 1122 Hz, respectively. As a comparison, with the GW frequency from 45 to 450 Hz, the orbital radii of the source GW170817 correspond to 163 and 57 km, respectively.

The merger event of double neutron star (DNS) system (GW170817) was detected by the gravitational-wave (GW) detectors (Advanced LIGO and Advanced Virgo) in 2017 for the first time, so their mass distribution has become a significant topic with the new round GW hunting (O3) in 2019. A few models (e.g. Gaussian, two-Gaussian, or mixture-Gaussian) were adopted to draw the mass distribution of observed Galactic DNS systems, however, there is no a confirmed model now due to the small size of DNS samples (N

This study compares the novel Asia Distal Lateral Tibial Locking Plate mechanical stability to that of the current anterolateral and medial tibial plates based on finite element analysis. Four-part fracture fragment model of the distal tibia was reconstructed using CAD software. A load was applied to simulate the swing phase of gait. The implant stress and the construct stiffness were compared. The results of the anterolateral plate and the medial plate were similar and the displacement values were determined lower than those in the medial plate. In the simulated distal tibia fracture, the Aplus Asia Distal Lateral Tibial Locking Plate and medial distal tibial plate tibia fixations will lead to a stiffer bone-implant construct compared to the anterolateral distal tibial plate. Moreover, the stress in the Aplus Asia Distal Lateral Tibial Locking Plate was lower than those for the medial distal tibial plate and anterolateral bone plates. The Aplus Asia Distal Lateral Tibial Locking Plate has better stabilization and is an anterolateral plate that avoids more soft tissue damage than other bone plates. The Aplus Asia Distal Lateral Tibial Locking Plate could be one of a suitable design in tibia distal fracture fixation.

Fast radio bursts (FRBs) are extremely strong radio flares lasting several milliseconds, most of which come from unidentified objects at a cosmological distance. They can be apparently repeating or not. In this paper, we analyzed 18 repeaters and 12 non-repeating FRBs observed in the frequency bands of 400-800 MHz from CHIME. We investigated the distributions of FRB isotropic-equivalent radio luminosity, considering the K correction. Statistically, the luminosity distribution can be better fitted by Gaussian form than by power-law. Based on the above results, together with the observed FRB event rate, pulse duration, and radio luminosity, FRB origin models are evaluated and constrained such that the gamma-ray bursts (GRBs) may be excluded for the non-repeaters while magnetars or neutron stars (NSs) emitting the supergiant pulses are preferred for the repeaters. We also found the necessity of a small FRB emission beaming solid angle (about 0.1 sr) from magnetars that should be considered, and/or the FRB association with soft gamma-ray repeaters (SGRs) may lie at a low probability of about 10%. Finally, we discussed the uncertainty of FRB luminosity caused by the estimation of the distance that is inferred by the simple relation between the redshift and dispersion measure (DM)., 12 pages, 2 figures, 2 tables. Accepted in Research in Astronomy and Astrophysics (RAA)

The properties of the young pulsars and their relations to the supernova remnants (SNRs) have been the interesting topics. At present, 383 SNRs in the Milky Way galaxy have been published, which are associated with 64 radio pulsars and 46 pulsars with high energy emissions. However, we noticed that 630 young radio pulsars with spin periods of less than half a second have been not yet observed the SNRs surrounding or nearby them, which arises a question of that could the two types of young radio pulsars with/without SNRs hold distinctive characteristics? Here, we employ the statistical tests on the two groups of young radio pulsars with (52) and without (630) SNRs to reveal if they share different origins. Kolmogorov-Smirnov (K-S) and Mann-Whitney-Wilcoxon (M-W-W) tests indicate that the two samples have the different distributions with parameters of spin period ($P$), derivative of spin period ($\dot P$), surface magnetic field strength ($B$), and energy loss rate ($\dot E$). Meanwhile, the cumulative number ratio between the pulsars with and without SNRs at the different spindown ages decreases significantly after $\rm10-20\,Kyr$. So we propose that the existence of the two types of supernovae (SNe), corresponding to their SNR lifetimes, which can be roughly ascribed to the low-energy and high-energy SNe. Furthermore, the low-energy SNe may be formed from the $\rm8-12\,M_{\odot}$ progenitor, e.g., possibly experiencing the electron capture, while the main sequence stars of $\rm12-25\,M_{\odot}$ may produce the high-energy SNe probably by the iron core collapse., Comment: 8 pages, 10 figures, 3 tables. Published in MNRAS

Binary systems with a neutron-star primary accreting from a companion star display variability in the X-ray band on time scales ranging from years to milliseconds. With frequencies of up to ~1300 Hz, the kilohertz quasi-periodic oscillations (kHz QPOs) represent the fastest variability observed from any astronomical object. The sub-millisecond time scale of this variability implies that the kHz QPOs are produced in the accretion flow very close to the surface of the neutron star, providing a unique view of the dynamics of matter under the influence of some of the strongest gravitational fields in the Universe. This offers the possibility to probe some of the most extreme predictions of General Relativity, such as dragging of inertial frames and periastron precession at rates that are sixteen orders of magnitude faster than those observed in the solar system and, ultimately, the existence of a minimum distance at which a stable orbit around a compact object is possible. Here we review the last twenty years of research on kHz QPOs, and we discuss the prospects for future developments in this field.

Based on the detected spin periods ( $P$ ) and inferred magnetic field strengths ( $B$ ) by the cyclotron resonance scattering features, we analyze the $B-P$ properties of Be/X-ray Pulsars (BeXPs). We find that the $P$ distribution of BeXPs exhibits a bimodal feature separated at $P\sim 40$ s, where the average spin period of the BeXPs with $P>40$ s ( $\langle P\rangle \sim 267$ s) is larger than that of the sources with $P

Correlated effects play a significant role in the study of quantum information processing. We investigate the two consecutive uses of the Pauli channels for quantum teleportation without resetting. We find that the existence of correlated action of noise channels is beneficial to improve the fidelity of noisy teleportation in Pauli channels, such as phase-damping, bit-flip and depolarizing channels. Namely, the fidelity increases with the increase of correlated parameter. Our study might provide a new perspective of enhancing the fidelity of quantum teleportation in noisy channels.

Based on the model of the accretion-induced magnetic field decay of a neutron star (NS), millisecond pulsars (MSPs) will obtain their minimum magnetic field when the NS magnetosphere radius shrinks to the stellar surface during the binary accretion phase. We find that this minimummagnetic field is related to the accretion rate Mdot as Bmin ~2.0*10^7 G( Mdot/Mdot_min)^1/2, where Mdot_min = 4.6*10^15 g/s is the average minimum accretion rate required for MSP formation and is constrained by the long-term accretion time, which corresponds to the companion lifetime, being less than the Hubble time. The value of Bmin is consistent with that of observed radio MSPs and accreting MSPs in low-mass X-ray binaries, which can be found the illustrated case of the minimum and present field strength of SAX J1808.4-3658. The prediction of the minimum magnetic field of MSPs would be the lowest field strength of NSs in the Universe, which could constrain the evolution mechanism of the magnetic field of accreting NSs., Comment: 5 pages, 2 figures

LIGO-Virgo has observed the gravitational waves (GWs) from the coalescence of binary black hole (BBH) and binary neutron star (BNS) during O1 and O2, and the ones from NS-BH are expected to be hunted in the operating O3 run. The population properties and mass distribution of NS-BH mergers are poorly understood now, thus researchers simulated their chirp mass ( ℳ ) distribution by a synthetic model, in which the BHs and NSs were inferred by LIGO-Virgo (O1/O2), and obtained the values in the range of 2.1 M ⊙ < ℳ < 7.3 M ⊙ . In this paper, we further simulate the GW frequency (f GW) distribution of NS-BH mergers by the above-stated synthetic model, with a basic binary system model through the Monte Carlo method. Our results predict that the median with 90% credible intervals is 165 − 64 + 475 Hz in the case of Schwarzschild BH when the system just before merger, and this GW frequency is expected to increase several times in the merger stage, which is lying in the frequency band of LIGO-Virgo, i.e., about 15 Hz to a few kHz. Our results provide an important reference for hunting the NS-BH mergers by the on-going O3 run of LIGO-Virgo.

To satisfy various requirements of different physics experiments, a new power modulation method of the lower hybrid wave (LHW) has been developed in Experimental Advanced Superconducting Tokamak (EAST), including the development of a control source combining software and hardware. Such modulation system is realized by the main positive-intrinsic-negative diode switch located at the oscillator. The LHW modulation system has been installed and tested, demonstrating that the modulation parameters can be controlled flexibly. The maximal modulation frequency is about 10 kHz, which is limited by the hardware circuit speed. The system has been successfully used to study the influence of LHW on the performances of plasma. Under the modulation of LHW, strong mitigation of edge-localized modes (ELMs) has been observed, and ELM pace-making technique has been demonstrated. Further experimental studies with the modulation system will be continued in EAST.

By the relativistic mean field theory and relevant weak-interactional cooling theory, the relativistic cooling properties in the conventional and hyperonic neutron star matter are studied. Also a comparison between the relativistic and non-relativistic results after taking consideration of the gravity correction is performed. The results show that the relativistic effect of neutrino emission reduces the neutrino emissivity, luminosity, and the cooling rate of stellar objects, in comparison with the non-relativistic case. In the neutron star matter without hyperon, the amplitude of the cooling rate reduction caused by the relativistic effect is maximal after taking the gravity correction into consideration, it attains 56% for a 2 M⊙ neutron star composed of conventional neutron star matter, and in the hyperonic matter the amplitude of reduction is minimal, about 38%.

By statistically analyzing the masses of twelve double neutron star (DNS) systems, it is concluded that the weighted mean value of DNS masses is (1.339±0.042) M⊙, where the weighted mean masses of the primary and companion stars are respectively (1.439±0.036) M⊙ and (1.239±0.020) M⊙. The mean value of the masses of primary stars is higher than that of companion stars, which indicates that the primary star may increase its mass by accretion, or the mass of its progenitor star is higher. Therefore, the physical process of supernova explosion through which the high-mass stars become NSs can be investigated hereby. Also it is found that the total masses of the DNSs span a narrow range of 2.5∼2.8 M⊙, implying that the companion stars might impact on the mass formation of DNSs. Moreover, the mass ratios of the DNSs (primaries to companions) approximate 1 (slightly larger than 1), indicating that the masses of the progenitors of primary stars are approximately equal to the masses of the progenitors of companion stars. By analyzing the distribution of the 12 DNSs in the surface magnetic field strength versus spin period (B-Ps) diagram, it is found that the surface magnetic field strength in the primary stars of the DNSs is ∼ 1010 Gs, and the spin period is ∼ 50 ms; while the two pulsars, i.e. PSR J1906+0746 and PSR J0737-3039B, are located in the region of normal pulsars in the B-Ps diagram, their surface magnetic field strength is ∼ 1012 Gs, suggesting that they might not be accelerated through accretion.

The gravitational waves (GWs) from the merger events of binary black hole (BH-BH) and binary neutron star (NS-NS) have been detected by LIGO-Virgo (O1 and O2). Besides, GWs from the NS-BH mergers have been recently reported and might be hopefully confirmed in the near future. The mass distributions of these merger events are poorly understood now; thus, LIGO-Virgo adopted a simple cut rule for chirp mass ($\mathcal{M}$) to distinguish the GW event candidates: $\mathcal{M}l2.1\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ for NS-NS, $2.1\text{ }\text{ }{M}_{\ensuremath{\bigodot}}l\mathcal{M}l4.35\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ for NS-BH, and $\mathcal{M}g4.35\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ for BH-BH. We tested its validity by simulating the chirp mass ($\mathcal{M}$) distributions in two synthetic models, i.e., Model Galaxy and Model LIGO, in which the masses of BHs and NSs are observed by the electromagnetic spectrum observations in our Galaxy and inferred by LIGO-Virgo detection (O1 and O2), respectively. The simulation shows that it is unsuitable for Model LIGO due to the BHs inferred by LIGO-Virgo are usually bigger than those in our Galaxy, and $\mathcal{M}$ of NS-BH events would distribute in the range of $2.1\text{ }\text{ }{M}_{\ensuremath{\bigodot}}l\mathcal{M}l7.3\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$, which partially overlaps with those of BH-BH events. Therefore, we suggest that the new searching round of LIGO-Virgo (e.g., O3) should carefully seek out the underlying NS-BH candidates in the range of $2.1\text{ }\text{ }{M}_{\ensuremath{\bigodot}}l\mathcal{M}l7.3\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$.

We report the discovery of a highly dispersed fast radio burst, FRB~181123, from an analysis of $\sim$1500~hr of drift-scan survey data taken using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The pulse has three distinct emission components, which vary with frequency across our 1.0--1.5~GHz observing band. We measure the peak flux density to be $>0.065$~Jy and the corresponding fluence $>0.2$~Jy~ms. Based on the observed dispersion measure of 1812~cm$^{-3}$~pc, we infer a redshift of $\sim 1.9$. From this, we estimate the peak luminosity and isotropic energy to be $\lesssim 2\times10^{43}$~erg~s$^{-1}$ and $\lesssim 2\times10^{40}$~erg, respectively. With only one FRB from the survey detected so far, our constraints on the event rate are limited. We derive a 95\% confidence lower limit for the event rate of 900 FRBs per day for FRBs with fluences $>0.025$~Jy~ms. We performed follow-up observations of the source with FAST for four hours and have not found a repeated burst. We discuss the implications of this discovery for our understanding of the physical mechanisms of FRBs., 7 pages, 3 figures, accepted for publication in ApJL

The spaceborne atomic clock is one of the core payloads of the Beidou III Global Navigation Satellite, which provides a highly stable time frequency reference for navigation satellites. At present, the Beidou III navigation satellites are equipped with the rubidium clock and the passive hydrogen clock. This paper presents the result of a long-term performance and life test of the spaceborne rubidium clock developed by Chinese Academy of Space Technology (Xi’an), for more than 430 days under vacuum condition on the ground. During the whole test, the rubidium clock is in the normal status, stable in performance and without any failure. The frequency stability of the clock reaches 5.31 × 10−15/100000 s (with drift removed), and the frequency drift rate tends to zero with the increase of working time and reaches −9.8 × 10−15/day before the end of the test. Data fitting of telemetry parameters of the rubidium clock has been performed, the result shows that there would be no significant performance degradation of the spaceborne rubidium clock during the 12-year mission period of the Beidou III navigation satellite.

Fast Radio Bursts (FRBs) are the short, strong radio pulses lasting several milliseconds. They are subsequently identified, for the most part, as emanating from unknown objects at cosmological distances. At present, over one hundred FRBs have been verified, classified into two groups: repeating bursts (20 samples) and apparently non-repeating bursts (91 samples). Their origins, however, are still hotly debated. Here,we investigate the statistical classifications for the two groups of samples to see if the non-repeating and repeating FRBs have different origins by employing Anderson-Darling (A-D) test and Mann-Whitney-Wilcoxon (M-W-W) test. Firstly, by taking the pulse width as a statistical variant, we found that the repeating samples do not follow the Gaussian statistics (may belong to a chi-square distribution), although the overall data and non-repeating group do follow the Gaussian. Meanwhile, to investigate the statistical differences between the two groups, we turn to M-W-W test and notice that the two distributions have different origins. Secondly, we consider the FRB radio luminosity as a statistical variant, and find that both groups of samples can be regarded as the Gaussian distributions under the A-D test, although they have different origins according to M-W-W tests. Therefore, statistically, we can conclude that our classifications of both repeaters and non-repeaters are plausible, that the two FRB classes have different origins, or each has experienced distinctive phases or been subject to its own physical processes., Comment: 7 pages, 5 figures, 3 tables. Accepted for publication in MNRAS

The evolution of neutron star (NS) magnetic field (B-field) has long been an important topic, which is still not yet settled down. Here, we analyze the NS B-fields inferred by the cyclotron resonance scattering features (CRSFs) for the high mass X-ray binaries (HMXBs) and by the magnetic dipole model for the spin-down pulsars. We find that the B-fields of both the 32 NSHMXBs and 28 young pulsars with the supernova remnants follow the log-normal distributions, with the average values of 3.4 * 10^12 G and 4.1 * 10^12 G respectively, which are further verified to come from the same continuous distribution by the statistical tests. These results declaim that the two methods of measuring NS B-fields are reliable for the above two groups of samples. In addition, since the NS-HMXBs have experienced the spin-down phase as the normal pulsars without accretion and then the spin-up phase by accretion, their ages should be about million years (Myrs). Our statistical facts imply that the B-fields of NS-HMXBs have little decayed in their non-accretion spin-down phases of ~ Myrs, as well as in their accretion phases of ~ 0.1Myrs., 8 pages, 2 figures, 4 tables, accepted by Astrophysics and Space Science

To track the formation and evolution links of the millisecond pulsars (MSPs) powered by accretion and rotation in the Galactic field, we investigate the spin period (P) and spin-down power (Edot) distributions of the MSPs observed at the wavebands of radio, X-ray, and {\gamma}-ray. We find that all but one (119/120) of the {\gamma}-ray MSPs have been detected with the radio signals (radio+{\gamma} MSPs); on the contrary, nearly half of the radio MSPs (118/237) have not been detected with {\gamma}-rays (radio-only MSPs). In addition, the radio+{\gamma} MSPs are shown to be the relative faster and more energetic objects ( ~ 3.28 ms and ~ 4.5 * 10^34 erg s^-1) compared with the radio-only MSPs ( ~ 4.70 ms and ~ 1.0 * 10^34 erg s^-1), while the spin periods of these two MSP populations are compatible with the log-normal distributions by the statistical tests. Most rotation-powered MSPs (RMSPs) with the radio eclipsing (31/34) exhibit the radio+{\gamma} signals, which share the faster spin ( ~ 2.78 ms) and larger spin-down power ( ~ 4.1 * 10^34 erg s^-1) distributions than the non-eclipsing ones ( ~ 4.19 ms, ~ 2.4 * 10^34 erg s^-1), implying the radio+{\gamma} MSPs to be younger than the radio-only MSPs. It is noticed that the spin distribution of the accretion-powered X-ray MSPs shows a clustering phenomenon around ~ 1.6-2.0 ms, which is not observed in RMSPs, hinting that the RMSPs may experience the multiple possible origins. Particularly, all the three super-fast spinning RMSPs with P ~ 1.4-1.6 ms exhibit the non-eclipsing, and we argue that they may be the distinctive sources formed by the accretion induced collapse (AIC) of white dwarfs., Comment: 9 pages, 2 figures, 6 tables

PSR B0919+06 is known for its abnormal emission phenomenon, where the pulse emission window occasionally shifts progressively in longitude and returns afterwards. The physical mechanism behind this phenomenon is still under investigation. In this paper, we present our ultra-wideband observation of this pulsar using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), with simultaneous measurements in the frequency ranges 280-780 MHz and 1250-1550 MHz. We have identified three abnormal events, each of which becomes less apparent as the frequency decreases. At 1400 MHz, the averaged profile slightly shifted after the first and third abnormal events, implying a relationship between abnormal event and profile variation. We also found a linear trend in the left-edge position of the averaged profiles between the first and third event as well as after the third event, suggesting the existence of a slow-drifting mode between the two major events. The second event has a comparatively small shift in phase and is thus categorized as a `small flare state'. During the third event, a sequence of approximately nine pulses was seen to significantly weaken in all frequency bands, likely associated with the pseudo-nulling observed at 150 MHz. A three-component de-composition analysis of the normal averaged profiles shows that the trailing component is dominant at our observing frequencies, while the centre component has a comparatively steeper spectrum. We found the overall flux density in an abnormal event to slightly differ from that in an ordinary state, and the difference shows a frequency dependence. A comparison of the normal, abnormal and dimmed averaged profile indicates that the leading component is likely to be stable in all states., Sci. China-Phys. Mech. Astron. 62,959504 (2019)

So far among the nineteen pairs of detected double neutron star (DNS) systems, it is a usual fact that the first-born recycled pulsar is detected, however the youngest DNS system PSR J1906+0746, with the characteristic age of 113 kyr, is one of the three detected DNS as a non-recycled and second-born NS, which is believed to be formed by an electron capture or a low energy ultra-stripped iron core-collapse supernova (SN) explosion. The SN remnant around PSR J1906+0746 is too dim to be observed by optical telescopes, then its x-ray flux limit has been given by Chandra. A reference pulsar PSR J1509-5850 with the young characteristic age of 154 kyr was chosen as an object of comparison, which has an SN remnant observed by Chandra and is believed to be formed by iron core SN explosion. We impose a restriction on the maximum kinetic energy of electron-capture (EC) SN explosion that induces the formation of PSR J1906+0746. The estimated result is (4–8)×1050 erg (1 erg = 10−7 J), which is consistent with that of the published simulations of the EC process, i.e., a lower value than that of the conventional iron core SN explosion of (1–2) × 1051 erg. As suggested, EC process for NS formation is pertained to the subluminous type Ic SN by the helium star with ONeMg core, thus for the first time we derived the kinetic energy of EC SN explosion of DNS, which may be reconciled with the recent observation of type Ic SN 2014ft with kinetic energy of 2 × 1050 erg.

We analyze the relation between the emission radii of twin kilohertz quasi-periodic oscillations (kHz QPOs) and the co-rotation radii of the 12 neutron star low mass X-ray binaries (NS-LMXBs) which are simultaneously detected with the twin kHz QPOs and NS spins. We find that the average co-rotation radius of these sources is r_co about 32 km, and all the emission positions of twin kHz QPOs lie inside the corotation radii, indicating that the twin kHz QPOs are formed in the spin-up process. It is noticed that the upper frequency of twin kHz QPOs is higher than NS spin frequency by > 10%, which may account for a critical velocity difference between the Keplerian motion of accretion matter and NS spin that is corresponding to the production of twin kHz QPOs. In addition, we also find that about 83% of twin kHz QPOs cluster around the radius range of 15-20 km, which may be affected by the hard surface or the local strong magnetic field of NS. As a special case, SAX J1808.4-3658 shows the larger emission radii of twin kHz QPOs of r about 21-24 km, which may be due to its low accretion rate or small measured NS mass (< 1.4 solar mass)., 7 pages, 5 figures, 1 table

In order to achieve steady state and high performance plasma in EAST, a new lower hybrid current drive system at a frequency of 4.6 GHz has been built. The system is composed of 24 continuous wave (CW) klystron amplifiers to generate 6MW/CW microwave, 24 standard rectangle waveguide transmission lines with water-cooling plate, a multi-junction grill composed of 576 active (in groups of 8) and 84 passive sub-waveguides arranged in 12 rows and 6 columns, and four sets of high voltage power supplies. The power value and the spectrum of the launched microwave from the antenna can be controlled by the low-power microwave circuits in front of the klystrons. The new LHCD system has been applied to the experiments on EAST tokmak since 2014, and the obtained results suggest that it is effective to couple the wave into plasma and drive plasma current.

This letter proposes an optical setup that is equivalent to an electrically controllable polarization element (ECPE). The principal axis of the ECPE can be changed by applying an electric signal on an electro-optic device of this setup. This ECPE can be applied for rotating a linear polarizer or a linear phase retarder with arbitrary phase retardation and can be operated at much higher rotation speed than the mechanical rotation. In contrast, the typical rotation speed of a mechanically rotating polarization element is $\sim 100$ Hz. The highest rotation speed of the ECPE is determined by the highest modulation frequency at which an electro-optic device can be correctly operated, which can range across several hertz to 300 kHz.

Pulsars posses extremely strong magnetic fields, and their magnetic axis does not coincide with their rotation axis, this causes the pulsars to emit electromagnetic radiations. Pulsars rely on their rotational energy to compensate for the energy loss caused by the electromagnetic radiation, which leads to the gradually decelerated spin of pulsars. According to the theoretical deduction, we have calculated the initial period of the Crab Nebula pulsar, and derived the period evolution of the pulsar at any time in the future under the effect of the electromagnetic radiation. Considered the possible existence of quadrupole moment in the mass distribution of a pulsar, the gravitational wave radiation will also make the pulsar spin down, hence the variation of spin period of the Crab pulsar under the effect of gravitational wave radiation is further analyzed. Finally, combining the two kinds of radiation mechanisms, the evolution of spin period of the Crab pulsar under the joint action of these two kinds of radiation mechanisms is analyzed.

We investigated the pulsar radio luminosity (L), emission efficiency (ratio of radio luminosity to its spin-down power E ˙ ), and death line in the magnetic field (B) versus spin period (P) diagram. We found that the dependence of pulsar radio luminosity on its spin-down power ( L − E ˙ ) is very weak, shown as L ∼ E ˙ 0.06 , which deduces an equivalent inverse correlation between emission efficiency and spin-down power as ξ ∼ E ˙ − 0.94 . Furthermore, we examined the distributions of radio luminosity of millisecond and normal pulsars and found that for the similar spin-down powers, the radio luminosity of millisecond pulsars is about one order of magnitude lower than that of the normal pulsars. The analysis of pulsar radio flux suggests that these correlations are not due to a selective effect but are intrinsic to the pulsar radio emission physics. Their radio radiations may be dominated by the different radiation mechanisms. The cut-off phenomenon of currently observed radio pulsars in B – P diagram is usually referred as the “pulsar death line”, which corresponds to E ˙ ≈ 10 30 erg s−1 and is obtained by the cut-off voltage of electron acceleration gap in the polar cap model of pulsar proposed by Ruderman and Sutherland. Observationally, this death line can be inferred by the actual observed pulsar flux S ≥ 1mJy and 1 kpc distance, together with the maximum radio emission efficiency of 1%. However, the observation data show that the 37 pulsars pass over the death line, including the recently observed two pulsars with long periods of 23.5 s and 12.1 s, which violate the prediction of the polar cap model. At present, the actual observed pulsar flux can reach 0.01mJy by FAST telescope. This will arise the observational limit of spin-down power of pulsars as low as E ˙ ≈ 10 28 erg s−1. This means that the new death line is downward shifted two orders of magnitude, which might be favorably referred as the “observational limit–line”. Accordingly, the pulsar theoretical model for the cut-off voltage of gap should be heavily modified.

Based on the detected kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries (NS-LMXBs), we investigate the evolution of the NS magnetosphere-disk structure along the Z track in the X-ray color-color diagram (CCD) for luminous Z sources, such as Cyg X-2, GX 5-1, GX 17+2, and Sco X-1. We find that the magnetosphere-disk radiusrinferred by kHz QPOs for all the sources shows a monotonically decreasing trend along the Z track from the horizontal branch (HB) to the normal branch (NB), implying that the dominated radiation components may dramatically change as the accretion disk moves toward the NS surface. In addition, the specific radius that corresponds to the HB/NB vertex is found to be aroundr ∼ 20 km, implying a potential characteristic position of transiting for the X-ray radiation mode. Furthermore, we find that the NBs that occur near the NS surface have a radius ofr ∼ 16−20 km, which is systematically smaller than those of HBs that have radii ofr ∼ 20−29 km. To interpret the relation between the CCD properties and the special magnetosphere-disk radii of Z sources, we suggest that the magnetic field lines corresponding to NB are “frozen-in” to the plasma, and move further inward with the shrinking of the NS magnetosphere-disk radius and pile up near the NS surface. They then form a strong magnetic field region aroundr ∼ 16−20 km, where the high magnetic energy density and high plasma mass density may dominate the radiation process in NB.

We analyze the properties of the binary millisecond pulsars (BMSPs), detected at radio and gamma-ray wavelengths, and further probe their correlations with the binary orbital parameters and companion masses to trace the possible evolutionary histories. We find that the BMSPs with the lowest-mass companions, (0.006-0.06)M-circle dot, have short orbital periods P-orb = 3.37 ms) than the radio-only BMSPs ( = 4.73ms). We propose that the latter systems are a later evolutionary phase of the former ones.

We describe PSR J1926-0652, a pulsar recently discovered with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Using sensitive single-pulse detections from FAST and long-term timing observations from the Parkes 64-m radio telescope, we probed phenomena on both long and short time scales. The FAST observations covered a wide frequency range from 270 to 800 MHz, enabling individual pulses to be studied in detail. The pulsar exhibits at least four profile components, short-term nulling lasting from 4 to 450 pulses, complex subpulse drifting behaviours and intermittency on scales of tens of minutes. While the average band spacing P3 is relatively constant across different bursts and components, significant variations in the separation of adjacent bands are seen, especially near the beginning and end of a burst. Band shapes and slopes are quite variable, especially for the trailing components and for the shorter bursts. We show that for each burst the last detectable pulse prior to emission ceasing has different properties compared to other pulses. These complexities pose challenges for the classic carousel-type models., Comment: 13pages with 12 figures

The gravitational wave event GW170817 is ascribed to the coalescence of a double neutron star (DNS) based on the multi-messenger observations. Based on the detected gravitational wave frequency by LIGO and the afterglow observations by the optical and Gamma-ray instruments, it is inferred that the outcome of coalescence kilonova of GW170817 is most probably the birth of a fast rotating sub-millisecond pulsar (SMSP), with the spin frequency of ∼ 1490 Hz (period of P ∼ 0.67 ms), and magnetic field of B ∼ 10 11 − 15 G depending on the magnetic reconstruction process of the new NS. The mass and radius of this new born SMSP is estimated to be about ∼ 2.6M⊙ and 12 − 25 km, respectively, then the EOS and nuclear composition of such a super-spinning and massive compact object is still open, after comparing with the predictions of the known EOS models. The observations of this new type of SMSP after GW170817 is proposed, and its extreme properties are investigated, for instance, its magnetic dipole spin-down induced energy dissipation rate is E ˙ ∼ 10 44 ( B / 10 12 G ) 2 erg/s, which is four orders of magnitudes more luminous than that of Crab pulsar, and accordingly its spin-down characteristic age is as short as 30 years. While considering the distance of the source at 130 million light years, the corresponding energy dissipation rate is E ˙ ∼ 10 35 ( B / 10 12 G ) 2 erg/s at the location of Crab pulsar, which could be observed by sensitive X, gamma and radio telescopes if this pulsar sweeps its radiation beam across the Earth.

In this paper we studied the neutron star's spin acceleration in the accretion process of the neutron star binary system, and the relation how the spin period changes with the accreted mass. We analyzed further the evolutions of both magnetic field and spin period of a neutron star, and compared the modeled results with the observational data of pulsars, to show that they are consistent with each other. Based on above studies, we investigated the effect of gravitational radiation on the spin-up process of a neutron star, and derived the change rate of the neutron star's spin period in the accretion process. We also estimated the critical angular velocity Ωcr, at which the accretion torque is balanced by that of gravitational radiation, and discussed the influence of gravitational radiation on the neutron star's spin evolution.

By means of the Monte Carlo method, we simulate the evolutionary distribution of accreting neutron stars (NSs) in the magnetic field versus spin period (B-P) diagram where the accretion induced magnetic-field decay model is exploited. The simulated results show that by mass accretion the B-P distribution of the accreting NS would evolve along the equilibrium period line to a region with low field and short period. The B-P distributions of the simulated accreting NSs are consistent with those of the observed millisecond pulsars (MSPs) after accretion of approximate to 0.1-0.2 M. We also test the effects of the initial magnetic field and the spin period on the evolved B-P distribution of the accreting NSs. It is shown that the evolved distributions of the simulated samples are independent of the selection of the initial condition when the NS magnetic field decays to a value less than approximate to 10(10) G. ((c) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

By reviewing the methods of mass measurements of neutron stars in four different kinds of systems, i.e., the high-mass X-ray binaries (HMXBs), low-mass X-ray binaries (LMXBs), double neutron star systems (DNSs) and neutron star-white dwarf (NS-WD) binary systems, we have collected the orbital parameters of 40 systems. By using the boot-strap method and the Monte-Carlo method, we have rebuilt the likelihood probability curves of the measured masses of 46 neutron stars. The statistical analysis of the simulation results shows that the masses of neutron stars in the X-ray neutron star systems and those in the radio pulsar systems exhibit different distributions. Besides, the Bayes statistics of these four different kind systems yields the most-probable probability density distributions of these four kind systems to be (1.340 ± 0.230)M8, (1, 505 ± 0.125)M8,(1.335 ± 0.055)M8 and (1.495 ± 0.225)M8, respectively. It is noteworthy that the masses of neutron stars in the HMXB and DNS systems are smaller than those in the other two kind systems by approximately 0.16M8. This result is consistent with the theoretical model of the pulsar to be accelerated to the millisecond order of magnitude via accretion of approximately 0.2M8. If the HMXBs and LMXBs are respectively taken to be the precursors of the BNS and NS-WD systems, then the influence of the accretion effect on the masses of neutron stars in the HMXB systems should be exceedingly small. Their mass distributions should be very close to the initial one during the formation of neutron stars. As for the LMXB and NS-WD systems, they should have already under- gone the process of suffcient accretion, hence there arises rather large deviation from the initial mass distribution.

Based on Rossi X-ray Timing Explorer (RXTE) observational data, we study the timing and spectral properties of some peculiar low-frequency (LF) quasi-periodic oscillations (QPOs), which have been found at the peak luminosity of the outburst of some transient black hole (BH) binaries: the 2005 outburst of GRO J1655-40, the 2003 outburst of H1743-322 and the 1998 outburst of XTE J1550-564. Appearing in the ultraluminous state, these QPOs from different sources show some common properties. The amplitude is very weak (less than 1 per cent) and the quality factor is larger than 6. Moreover, these QPOs (about several Hz) sometimes show up simultaneously with another QPO (about 10 Hz), but their frequencies are not harmonically related. We also find that the frequencies of these QPOs are inversely correlated with the mass of the BH, which implies that these QPOs might be correlated with the innermost stable circular orbit. The QPO frequency is also negative correlated with the inner disc radius among BHs. However, its frequency is too low to ascribe it to the Keperlian orbit frequency. Moreover, we discuss the physical origin of these QPOs and we suggest that they are not produced by the viscous variability of the inner disc either.

We analyzed 186 binary pulsars (BPSRs) in the magnetic field versus spin period (B-P) diagram, where their relations to the millisecond pulsars (MSPs) can be clearly shown. Generally, both BPSRs and MSPs are believed to be recycled and spun-up in binary accreting phases, and evolved below the spin-up line setting by the Eddington accretion rate ($\dot{M}{\bf \simeq}10^{18} g/s$). It is noticed that most BPSRs are distributed around the spin-up line with mass accretion rate $\dot{M}=10^{16} g/s$ and almost all MSP samples lie above the spin-up line with $\dot{M}\sim10^{15} g/s$. Thus, we calculate that a minimum accretion rate ($\dot{M}\sim 10^{15} g/s$) is required for the MSP formation, and physical reasons for this are proposed. In the B-P diagram, the positions of BPSRs and their relations to the binary parameters, such as the companion mass, orbital period and eccentricity, are illustrated and discussed. In addition, for the seven BPSRs located above the limit spin-up line, possible causes are suggested., Comment: 8 pages,6figures, 1 table; accepted for publication in Astrophysics and Space Science

We investigate the correlation between the frequencies of the twin kilohertz quasi-periodic oscillations (kHz QPOs) and the neutron star (NS) spins in low mass X-ray binaries (LMXBs), based on the data sets of 12 sources with simultaneously detected twin kHz QPOs and NS spins, and find that the histogram of the ratio between the frequency difference of twin kHz QPOs ({\Delta}{\nu} = {\nu}2 - {\nu}1) and NS spin {\nu}s shows a non-uniform distribution with a gap at {\Delta}{\nu}/{\nu}s ~ 0.65. We try to classify the 12 sources into two categories according to this gap: (I) The slow rotators with ~ 311 Hz, XTE J1807.4-294, 4U 1915-05, IGR J17191-2821, 4U 1702-43, 4U 1728-34 and 4U 0614+09 follow a relation {\Delta}{\nu}/{\nu}s > 0.65; (II) The fast rotators with ~ 546 Hz, SAX J1808.4-3658, KS 1731-260, Aql X-1, 4U 1636-53, SAX J1750.8-2900 and 4U 1608-52 satisfy the relation {\Delta}{\nu}/{\nu}s < 0.65. However, the linear fittings of {\Delta}{\nu} versus {\nu}s relations of group (I) and (II) are unsatisfactory to ensure any certain correlations. We suggest that this phenomenon may arise from the fact that most measured kHz QPOs and spins satisfy the conditions of 1.1 {\nu}s < {\nu}2 < 1300Hz and {\Delta}{\nu} decreasing with {\nu}2. Apparently, the diversified distribution of {\Delta}{\nu}/{\nu}s refutes the simple beat-frequency model, and the statistical correlations between the twin kHz QPOs and NS spins may arise from the magnetosphere-disk boundary environments, e.g., co-rotation radius and NS radius, that modulate the occurrences of X-ray signals. Furthermore, we also find that the distribution of the ratio of {\nu}2 to {\nu}1 clusters around the value of ~ 3 : 2, which shows no obvious correlation with NS spins., Comment: 7 pages, 4 figures and 2 tables, accepted by Monthly Notices of the Royal Astronomical Society

The various types of pulsars are classified in the magnetic and spin period (B-P) diagram, by which one can recognize their properties there. We also investigate the relation of radio pulsars and X-ray neutron stars, and their distribution characteristics, implying their evolution links. B-P diagram is divided by the special lines, e.g. spin-up line and "death line", which indicate the evolution information of pulsars. Like Hertzsprung-Russell (H-R) diagram of showing the stellar evolution or "lives of stars", we try to develop B-P diagram as a function of representing the evolution track of neutron star.

We perform a Monte Carlo simulation to investigate the distribution and evolution of 66 mass measured pulsars. We get the best fits to the distribution at 1.35 ± 0.27M⨀ (1σ confidence level). In addition, we notice bimodal distributions in 1.34 ± 0.15M⨀ and 1.48 ± 0.53M⨀, this can be led to the idea that radio pulsars in binary systems have recycled. Thus we divide the data according to the characteristic spin period into two groups, millisecond pulsars (MSPs), P Spin ≤ 20 ms and less recycled pulsars P Spin ≥ 20 ms , respectively. We show that the distributions of MSPs at 1.42 ± 0.36M⨀, and 1.32 ± 0.18M⨀ for less recycled pulsars. As such, the mass of MSPs are heavier than those in less recycled pulsars by ~ 0.1M⨀, since they accreting material from their companions. On the other hand, the formation of heavier pulsars from the accretion induced collapse of accreting white dwarfs, must be invoked.

With accretion of mass from an evolving companion star, a neutron star can be spun up to an equilibrium period, which is set by the Kepler orbital period at the magnetosphere radius, expressed as a proportional relation between the spin period and magnetic field strength. The spin-up line relationship can be also expressed as a relation between period (P) and period derivative (Ṗ) for the pulsars with dipole radiation. All binary pulsars should lie below the spin-up line, if they accrete the sufficient masses from companions. So, we investigate the distribution of isolated and binary pulsars in the period (P) and magnetic field (B) diagram to see their positions relative to the spin-up line. It is found that the eight binary pulsars (of total 172) are above the spin-up line, thus we analyze their properties and present the possible process of their formations.

Age of a pulsar is a useful parameter, but it is difficult to get the age from observation. We can only derive the characteristic age from the observed parameters: spin period (P) and period derivative (Ṗ). In this paper, we discussed the relationship between characteristic age and magnetic field of a pulsar. Monte Carlo simulation is also used to support the idea: it is useless to study the magnetic field evolution using characteristic age. From some observation evidences we get that: the characteristic age cannot be used as true age, especially for millisecond pulsar (MSP). The difference between them is also discussed. From the studying of breaking index and MSP's initial spin period (P0), we get the conclusion that: the problem cannot be resolved using different radiation models.

We take the recently published data of twin kHz quasi-period oscillations (QPOs) in neutron star (NS) lowmass X-ray binaries (LMXBs) as the samples, and investigate the morphology of the samples, which focuses on the quality factor, peak frequency of kHz QPOs, and try to infer their physical mechanism. We notice that: (1) The quality factors of upper kHz QPOs are low (2 ~ 20 in general) and increase with the kHz QPO peak frequencies for both Z and Atoll sources. (2) The distribution of quality factor versus frequency for the lower kHz QPOs are quite different between Z and Atoll sources. For most Z source samples, the quality factors of lower kHz QPOs are low (usually lower than 15) and rise steadily with the peak frequencies except for Sco X-1, which drop abruptly at the frequency of about 750 Hz. While for most Atoll sources, the quality factors of lower kHz QPOs are very high (from 2 to 200) and usually have a rising part, a maximum and an abrupt drop. (3) There are three Atoll sources (4U 1728-34, 4U 1636-53 and 4U 1608-52) of displaying very high quality factors for lower kHz QPOs. These three sources have been detected with the spin frequencies and sidebands, in which the source with higher spin frequency presents higher quality factor of lower kHz QPOs and lower difference between sideband frequency and lower kHz QPO frequency., 8 pages, 8 figures, published

Using the recently published data of twin kHz quasi-period oscillations (QPOs) in neutron stars of low-mass X-ray binaries (LMXBs), we study the different profiles between bright Z sources and less luminous Atoll sources. The quality factors of upper kHz QPOs show a narrow distribution both for Z sources and Atoll sources, which concentrate at 7.98 and 9.75, respectively. The quality factors of lower kHz QPOs show a narrow distribution for Z sources and a broader distribution for Atoll sources, which concentrate at 5.25 and 86.22, respectively. In order to investigate the relation between the quality factor and the peak frequency of kHz QPOs, we fit the data with power-law, linear, and exponential functions, respectively. There is an obvious trend that the quality factors increase with the peak frequencies both for upper and lower QPOs. The implications of our results are discussed (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)