Search

PSR B0820 + 02 is known to exhibit the subpulse drifting phenomenon, which carries vital information about the pulsar radiation process. In this work, we studied the subpulse drifting of PSR B0820 + 02 at a central frequency of 1250 MHz using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Thanks to the superior sensitivity of FAST, we found that PSR B0820 + 02 shows four distinct subpulse drifting modes (A, B, C, and D), the last three of which have not been reported before. The drifting periodicities of these four modes are found to be 4.3P1, 6.4P1, 8.2P1, and 10.3P1 (P1 is the pulse period), respectively. No null pulse is found in our FAST observation. By comparing the energy distribution of single pulses of all four modes, we found that mode A has the highest energy and mode D has the lowest energy. Finally, we interpreted the drift modes in terms of the carousel model, and showed that if B0820 + 02’s different drift modes are due to aliasing effects, the carousel rotation period of P4 lies in the range 29P1–33P1. The new subpulse drifting phenomena of PSR B0820 + 02 reported here provide a unique opportunity for understanding the mechanism and radiation geometry of pulsar radio radiation.

The multi-band observation, from radio to gamma-ray, plays a crucial role in constraining the emission physics and geometrical magnetospheric models of the pulsars. In this paper, We use three-dimensional magnetospheric model, with the joint of the annular gap (AG) and core gap (CG) model, to simulate the radio and gamma-ray light curves for two representative pulsars, a millisecond pulsar J2302+4442 and a young pulsar J0659+1414. It is found that for PSR J2302 + 4442, the simulated magnetic inclination angle α and viewing angle ζ are 34 ∘ and 46 ∘ , and for PSR J0659 + 1414 are 45 ∘ and 33 ∘ . This implies that the radio and gamma-ray pulse emission originates from different magnetospheric regions and the radiation geometry for millisecond and young pulsar is different. The studies show that the joint of the AG and CG model can describe the light curves not only for millisecond pulsars but also for young pulsars, and hence it can be used to explain the multi-wavelength observations of pulsars.

The emission geometries, e.g. the emission region height, the beam shape, and radius-to-frequency mapping, are important predictions of pulsar radiation model. The multi-band radio observations carry such valuable information. In this paper, we study two bright pulsars, (PSRs B0329+54 and B1642-03) and observe them in high frequency (2.5 GHz, 5 GHz, and 8 GHz). The newly acquired data together with historical archive provide an atlas of multi-frequency profiles spanning from 100 MHz to 10 GHz. We study the frequency evolution of pulse profiles and the radiation regions with the these data. We firstly fit the pulse profiles with Gaussian functions to determine the phase of each component, and then calculate the radiation altitudes of different emission components and the radiation regions. We find that the inverse Compton scattering (ICS) model can reproduce the radiation geometry of these two pulsars. But for PSR B0329+54 the radiation can be generated in either annular gap (AG) or core gap (CG), while the radiation of PSR B1642-03 can only be generated in the CG. This difference is caused by the inclination angle and the impact angle of these two pulsars. The relation of beaming angle (the angle between the radiation direction and the magnetic axis) and the radiation altitudes versus frequency is also presented by modelling the beam-frequency evolution in the ICS model. The multi-band pulse profiles of these two pulsars can be described well by the ICS model combined with the CG and AG.

We present integrated pulse profiles at 5~GHz for 71 pulsars, including eight millisecond pulsars (MSPs), obtained using the Shanghai Tian Ma Radio Telescope (TMRT). Mean flux densities and pulse widths are measured. For 19 normal pulsars and one MSP, these are the first detections at 5~GHz and for a further 19, including five MPSs, the profiles have a better signal-to-noise ratio than previous observations. Mean flux density spectra between 400~MHz and 9~GHz are presented for 27 pulsars and correlations of power-law spectral index are found with characteristic age, radio pseudo-luminosity and spin-down luminosity. Mode changing was detected in five pulsars. The separation between the main pulse and interpulse is shown to be frequency independent for six pulsars but a frequency dependence of the relative intensity of the main pulse and interpulse is found. The frequency dependence of component separations is investigated for 20 pulsars and three groups are found: in seven cases the separation between the outmost leading and trailing components decreases with frequency, roughly in agreement with radius-to-frequency mapping; in eleven cases the separation is nearly constant; in the remain two cases the separation between the outmost components increases with frequency. We obtain the correlations of pulse widths with pulsar period and estimate the core widths of 23 multi-component profiles and conal widths of 17 multi-component profiles at 5.0~GHz using Gaussian fitting and discuss the width-period relationship at 5~GHz compared with the results at at 1.0~GHz and 8.6~GHz.

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has the potential to discover many new pulsars and new phenomena. In this paper we mainly concentrate on how FAST can impact study of the pulsar emission mechanism and magnetospheric dynamics. Several observational programs heading to this direction are reviewed. To make full use of the superior performance of FAST and maximize the scientific outcome, these programs can be arranged in different phases of FAST according to their demands for observational conditions. We suggest that programs can be performed following the test phase, which are observations of multifrequency mean pulse profiles, anomalous X-ray pulsars (AXPs)/soft gamma-ray repeaters (SGRs), mode changing, drifting subpulse and nulling. The long-term monitoring can be carried out for mode changing, AXPs/SGRs and precessional pulsars. Others programs, including polarization observations of radio and γ-ray pulsars, searching for weak pulse components, and multifrequency observations of subpulse drifting, microstructure and giant pulses, can be conducted in all the normal operating phases (the first and second phases). These programs will push forward the frontier in this field in different respects. The search for sub-millisecond pulsars and follow-up observations of their emission properties are very important projects for FAST, but they may be covered by other papers in this mini-volume; therefore, they are not discussed here.

Pulsars have been found more than 40 years. Observations from radio to gamma-rays present abundant information. However, the radiation mechanism is still an open question. It is found that the annular gap could be formed in the magnetosphere of pulsars (neutron stars or quark stars), which combines the advantages of the polar cap, slot gap and outer gap models. It is emphasized that observations of some radio pulsars, normal and millisecond gamma-ray pulsars (MSGPs) show that the annular gap would play a very important role. Here we show some observational and theoretical evidences about the annular gap. For example, bi-drifting sub-pulses; radio and gamma-ray millisecond pulsars and so on.

In traditional classes, having many questions from learners is important because these questions indicate difficult points for learners and for teachers. This paper proposes a FAQ-based e-Learning environment to support Japanese language learning that focuses on learner questions. This knowledge sharing system enables learners to interact and share information and knowledge through FAQ and e-mail. Teachers contribute answers to discussion among learners. The system also allows learners to discuss and collaborate, stimulating their motivation to study Japanese as a foreign language. All questions are stored in a FAQ database, allowing other learners to reuse resources, helping learners learn by themselves and reduce teacher workloads.

Pulsars have been recognized as normal neutron stars, but sometimes argued as quark stars. {\it Sub-millisecond pulsars, if detected, would play an essential and important role in distinguishing quark stars from neutron stars.} We focus on the formation of such sub-millisecond pulsars in this paper. A new approach to form a sub-millisecond pulsar (quark star) via accretion induced collapse (AIC) of a white dwarf is investigated here. Under this AIC process, we found that: (1) almost all the newborn quark stars could have an initial spin period of $\sim 0.1$ ms; (2) the nascent quark stars (even with a low mass) have sufficiently high spin-down luminosity and satisfy the conditions for pair production and sparking process to be as sub-millisecond radio pulsars; (3) in most cases, the timescales of newborn quark stars in the phase of spin period $< 1$ (or $

It is found that pulsar radiation altitude ratios between different radio frequencies are weak-dependent on the inclination angle α. This is proved via series expansion techniques and illustrated by using pulsar examples of PSR B0329+54, B1508+55, B2016+28, B1133+16, and B2319+60. It is emphasized that this α-weak-dependent radiation altitude ratio offers a good tool to test pulsar radiation models. We use the measured altitude ratios to constrain the parameter space for the Ruderman-Sutherland model and the inverse Compton scattering model. It is found that the Ruderman-Sutherland model is not compatible with the measured altitude ratios, while the results are compatible with the inverse Compton scattering model. The potential possible applications of this method in studying pulsar timing and in studying pulsar high energy radiation are also discussed.

The region in which pulsars radiate is very important to constrain pulsar emission mechanisms. A three-dimensional (3D) method to calculate emission heights is developed in this paper. As an example, radiation regions for different components at different frequencies have been calculated for PSR B2111+46. Emission components at seven frequencies are fitted with Gaussian components, then the radiation heights for emission components are calculated. We found that different emission components, even if at the same radio frequency, are radiated from different heights. This is probably a common phenomena and challenges any emission mechanisms. The inverse Compton scattering emission model for pulsar radio emission can explain these results well.

Observational constraints on the radio and γ-ray emission regions of PSR B1055-52 seen through our line of sight are presented by analysing the position angle curves of radio linear polarization and fitting the observed pulse widths of radio and γ-ray pulses and the phase offsets between them. Aberration, retardation and magnetic field sweep back effects that can cause additional phase offset between the emissions from different locations are taken into account. The following conclusions are obtained. (i) The radio main pulse and γ-ray pulses are emitted from the same pole, while the radio interpulse is emitted from the opposite pole. (ii) The interpulse emission region locates on the open field lines much closer to the magnetic axis than those of the main pulse, and the emission altitudes are higher than those of the main pulse. (iii) At each pole, there are probably two groups of field lines where radio emission is generated, of which the outer one consists of open field lines near (or including) the last open field lines and the inner one consists of open field lines from very near the magnetic pole to approximately the midway between the magnetic axis and the last open field lines. (iv) The γ-ray pulse comes from inner open field lines rather than from the last open field lines, and the emission altitudes are beyond the null charge surface.

In the inner annular gap (IAG) model the γ-ray radiation sources are suggested to be located close to the null charge surface (NCS). A method to explore two geometric parameters ( κ , λ ) of the IAG model is given in this paper. Pulsar population statistics are proposed to test the radiation locations of γ-ray pulsars. Within the IAG model, predictions for the GLAST observation of γ-ray pulsars are also made.

PSR B1821$-$24 is a solitary millisecond pulsar (MSP) which radiates multi-wavelength pulsed photons. It has complex radio, X-ray and $\gamma$-ray pulse profiles with distinct peak phase-separations that challenge the traditional caustic emission models. Using the single-pole annular gap model with suitable magnetic inclination angle ($\alpha=40^\circ$) and viewing angle ($\zeta=75^\circ$), we managed to reproduce its pulse profiles of three wavebands. It is found that the middle radio peak is originated from the core gap region at high altitudes, and the other two radio peaks are originated from the annular gap region at relatively low altitudes. Two peaks of both X-ray and $\gamma$-ray wavebands are fundamentally originated from annular gap region, while the $\gamma$-ray emission generated from the core gap region contributes somewhat to the first $\gamma$-ray peak. Precisely reproducing the multi-wavelength pulse profiles of PSR B1821$-$24 enables us to understand emission regions of distinct wavebands and justify pulsar emission models., Comment: Accepted for publication in ApJ

The origin of the 6.67 hr period X-ray source, 1E161348-5055, in the young supernova remnant RCW 103 is puzzling. We propose that it may be the descendant of a Thorne-Zytkow Object (TZO). A TZO may at its formation have a rapidly spinning neutron star as a core, and a slowly rotating envelope. We found that the core could be braked quickly to an extremely long spin period by the coupling between its magnetic field and the envelope, and that the envelope could be disrupted by some powerful bursts or exhausted via stellar wind. If the envelope is disrupted after the core has spun down, the core will become an extremely long-period compact object, with a slow proper motion speed, surrounded by a supernova-remnant-like shell. These features all agree with the observations of 1E161348-5055. TZOs are expected to have produced extraordinary high abundances of lithium and rapid proton process elements that would remain in the remnants and could be used to test this scenario., Comment: 6 pages

The electric properties of pulsar’s inner annular gap are explored in this paper. Under two main assumptions, (1) the pulsar is alive, (2) the total charge of pulsar should not vary with time, the condition for the acceleration of negative particle in the annular region is derived. The acceleration condition is j − ⩾ 0.5 j + , i.e., the current carried by negative particles is greater than or equal to 0.5 times of the current carried by positive particles. This condition holds even when the backward flow of positive particles exists in the annular region. It is noted that the outflow of negative particles offers good opportunities to understand the current closure problem of pulsar as well as wide radiation beam of pulsar observed at high energy band.

Aims. We use the supernova-GRB (γ-ray burst) association and assume that the GRB asymmetric explosions produce pulsars in order to test the consistency of distributions of modeled and observed pulsar-kick velocities. Methods. The deduced distribution of kick velocity from the model of GRB and the observed kick distribution of radio pulsars are checked by a K-S test. Results. These two distributions are found to come from the same parent population. Conclusions. This result may indicate that GRBs could really be related to supernova and that the asymmetry of GRB associated with supernova would cause the pulsar kick.

Mean pulse profiles and polarization parameters at 435, 660 or 1500 MHz obtained using the ATNF Parkes radio telescope are presented for 66 southern pulsars. About half of these pulsars were discovered in the Parkes southern pulsar survey and most have no previously published polarization parameters. Where possible, beam impact parameters and inclination angles are computed assuming a circular beam geometry and the rotating-vector model. Implications of the results for models of the pulse emission mechanism are briefly discussed.

The process of inverse Compton scattering (ICS) of high-energy particles off the thermal photons above the pulsar polar cap is the dominant mechanism causing polar gap breakdown. In this paper, an approximate analytic description of the parameters of the two modes of the ICS gap, namely, the "resonant ICS gap" and the "thermal ICS gap," are derived under the assumption of a multipolar magnetic field configuration in the neutron star's vicinity. For typical values of P, B, and T, the thermal ICS gap usually has a lower height and smaller potential drop but results in larger Lorentz factors for the secondary particles ejected from the gap. Above the polar gap, the secondary particles do not keep the energy gained from the primary γ-rays, as expected. They will lose much of their energy via different mechanisms, among which the ICS process is dominant, as pointed out previously by different authors. We calculate the height-dependent Lorentz factor decrease of the secondary particles via ICS above the gap. It is found that, for a certain polar cap temperature and a temperature of the whole neutron star surface, the particles will lose most of their energy as a result of the "resonant" scattering within a not very high altitude (usually ~0.1-0.01 neutron star radii) after they escape from the gap, then keep nearly unchanged energies for a long distance of several to a dozen stellar radii (the so-called Lorentz platform), and then endure severe energy loss again, due to the "nonresonant" scattering dominant at higher altitudes. This effect has a direct implication for pulsar radiation theories, if pulsar radio emission comes from tens or hundreds of kilometers above the neutron star surface, which is just the height range of the "Lorentz platform" that we discuss. We caution that, if the polar cap temperature of a pulsar is relatively high, but not high enough to switch its gap to the "thermal mode," the secondary particles will receive lower energies from the resonant ICS gap but endure severe energy loss above the gap, so that their Lorentz factors may be below the possible threshold for pulsar radio emission. In this case, the pulsar will "null," or be radio-quiet. Some pulsars' "nulling" feature and Geminga's radio-quiet behavior may be a consequence of this effect.

It is found that two radiation processes can cause pulsar inner gap breakdown, namely, the curvature radiation (CR) and the inverse Compton scattering (ICS) of high-energy particles off the thermal photons in the neutron star vicinity. The ICS photons are usually more energetic than the CR photons, so that the ICS process is the dominant mechanism to cause pulsar inner gap breakdown. For the ICS process, there are two preferred frequencies for the scattered γ-rays: (1) ωs = 2γωB, which is attributed to the resonant scattering, and (2) ωs ~ γ2(2.82kT), which is mainly the contribution of the thermal-peak photons, which are usually more energetic. Thus we obtain three modes for pulsar inner gap sparking, namely, the "resonant ICS mode," the "thermal-peak ICS mode," and the "CR mode." A more energetic mode is more likely to dominate the gap-sparking process if the mean free path of the electrons (or positrons) is smaller than the gap height, which is equal to the mean free path of the γ-rays before being absorbed by the magnetic fields. The mean free paths of the electrons (or positrons) for the two ICS modes are functions of the surface temperature of a neutron star, so that we can obtain two "critical temperatures" to distinguish the three modes of pulsar inner gap. If the surface temperatures of the neutron stars fluctuate around the "critical temperatures," the gap properties will change suddenly, which will result in a switching effect in pulsar radiation. The observed "mode changing" phenomenon of some pulsars can be explained by switching between the resonant ICS mode and the thermal-peak ICS mode. The young pulsars near the "birth line" are dominated by the resonant ICS mode, while the pulsars near the "death line" and the millisecond pulsars near the "appearance line" are more likely dominated by the thermal-peak ICS mode.

Timing observations from the Parkes 64-m radio telescope for 165 pulsars between 1990 and 2011 have been searched for period glitches. A total of 107 glitches were identified in 36 pulsars, where 61 have previously been reported and 46 are new discoveries. Glitch parameters were measured by fitting the timing residual data. Observed relative glitch sizes \Delta\nu_g/\nu range between 10^-10 and 10^-5, where \nu = 1/P is the pulse frequency. We confirm that the distribution of \Delta\nu_g/\nu is bimodal with peaks at approximately 10^-9 and 10^-6. Glitches are mostly observed in pulsars with characteristic ages between 10^3 and 10^5 years, with large glitches mostly occurring in the younger pulsars. Exponential post-glitch recoveries were observed for 27 large glitches in 18 pulsars. The fraction Q of the glitch that recovers exponentially also has a bimodal distribution. Large glitches generally have low Q, typically a few per cent, but large Q values are observed in both large and small glitches. Observed time constants for exponential recoveries ranged between 10 and 300 days with some tendency for longer timescales in older pulsars. Shorter timescale recoveries may exist but were not revealed by our data which typically have observation intervals of 2 - 4 weeks. For most of the 36 pulsars with observed glitches, there is a persistent linear increase in \dot\nu in the inter-glitch interval. Where an exponential recovery is also observed, the effects of this are superimposed on the linear increase in \dot\nu. In some cases, the slope of the linear recovery changes at the time of a glitch. The \ddot\nu values characterising the linear changes in \dot\nu are almost always positive and, after subtracting the magnetospheric component of the braking, are approximately proportional to the ratio of |\dot\nu| and the inter-glitch interval, as predicted by vortex-creep models., Comment: Accepted for publication in MNRAS

In the framework of the three-dimensional (3D) annular gap model with reasonable parameters (the magnetic inclination angle \alpha = 45 deg and the view angle \zeta = 63 deg), we first use the latest hight energy data to self-consistently calculate radio, X-ray, gamma-ray and TeV (MAGIC and VERITAS) light curves, phase-averaged spectrum and phase-resolved spectra for the Crab pulsar. It is found that the acceleration electric field and potential in the annular gap and core gap are huge enough in the several tens of neutron star radii. The pulsed emission of radio, X-ray, gamma-ray and TeV are mainly generated from the emission of primary particles or secondary particles with different emission mechanisms in the nearly similar region of the annular gap located in the only one magnetic pole, which leads to the nearly "phase-aligned" multi-wavelength light curves. The emission of peak 1 (P1) and peak 2 (P2) is originated from the annular gap region near the null charge surface, while the emission of bridge is mainly originated from the core gap region. The phase-averaged spectrum and phase-resolved spectra of the Crab pulsar from soft X-ray to TeV band are produced by four components: synchrotron radiation from CR-induced and ICS-induced pairs dominates the X-ray band to soft gamma-ray band (100 eV to 10 MeV); curvature radiation and synchrotron radiation from the primary particles mainly contribute to gamma-ray band (10 MeV to \sim 20 GeV); ICS from the pairs significantly contributes to the TeV gamma-ray band (\sim 20 GeV to 400 GeV). The multi-wavelength pulsed emission from the Crab pulsar has been well modeled with the annular gap and core gap model. To distinguish our single magnetic pole model from two-pole models, the convincing values of the magnetic inclination angle and the viewing angle will play a key role., Comment: 12 pages, 7 figures, 3 tables; published in ApJ on March 12. Due to the character limitation, the abstract here has been adopted a shortened version

The inverse Compton scattering (ICS) model can explain various pulse profile shapes and diversity of pulse profile evolution based on the mechanism that the radio emission is generated through inverse Compton scattering between secondary relativistic particles and radio waves from polar gap avalanches. In this paper, we study the parameter space of ICS model for 15 pulsars, which share the common pulse profile evolution phenomena that the pulse profiles are narrower at higher observing frequencies. Two key parameters, the initial Lorentz factor and the energy loss factor of secondary particles are constrained using the least square fitting method, where we fit the theoretical curve of the "beam-frequency mapping" of the ICS model to the observed pulse widths at multiple frequencies. The uncertainty of the inclination and viewing angles are taken into account in the fitting process. It is found that the initial Lorentz factor is larger than 4000, and the energy loss factor is between 20 and 560. The Lorentz factor is consistent with the prediction of the inner vacuum gap model. Such high energy loss factors suggest significant energy loss for secondary particles at altitudes of a few tens to hundreds of kilometers., 32 pages,18 figures, Accepted by the ApJ

The Vela pulsar represents a distinct group of {\gamma}-ray pulsars. Fermi {\gamma}-ray observations reveal that it has two sharp peaks (P1 and P2) in the light curve with a phase separation of 0.42 and a third peak (P3) in the bridge. The location and intensity of P3 are energy-dependent. We use the 3D magnetospheric model for the annular gap and core gap to simulate the {\gamma}-ray light curves, phase-averaged and phase-resolved spectra. We found that the acceleration electric field along a field line in the annular gap region decreases with heights. The emission at high energy GeV band is originated from the curvature radiation of accelerated primary particles, while the synchrotron radiation from secondary particles have some contributions to low energy {\gamma}-ray band (0.1 - 0.3 GeV). The {\gamma}-ray light curve peaks P1 and P2 are generated in the annular gap region near the altitude of null charge surface, whereas P3 and the bridge emission is generated in the core gap region. The intensity and location of P3 at different energy bands depend on the emission altitudes. The radio emission from the Vela pulsar should be generated in a high-altitude narrow regions of the annular gap, which leads to a radio phase lag of ~ 0.13 prior to the first {\gamma}-ray peak., Comment: 9 pages, 8 figures, 2 tables, accepted by ApJ

Mean pulse total intensity and polarization data at 1560 MHz are presented for 45 southern pulsars. The observations were made during 1988 at Parkes using a filter-bank polarimeter system. The results are discussed in terms of the rotating vector model for pulse polarization. Notable results include a highly polarized interpulse pulsar and several pulsars with very wide mean pulse profiles

The relationship between pulsar-like compact stars and gravitational waves is briefly reviewed. Due to regular spins, pulsars could be useful tools for us to detect ~nano-Hz low-frequency gravitational waves by pulsar-timing array technique; besides, they would also be ~kilo-Hz high-frequency gravitational wave radiators because of their compactness. The wave strain of an isolate pulsar depends on the equation state of cold matter at supra-nuclear densities. Therefore, a real detection of gravitational wave should be very meaningful in gravity physics, micro-theory of elementary strong interaction, and astronomy.

The pulse profile of PSR B1133+16 is usually regarded as a conal-double structure. However, its multifrequency profiles cannot simply be fitted with two Gaussian functions, and a third component is always needed to fit the bridge region (between two peaks). This would introduce additional, redundant parameters. In this paper, through a comparison of five fitting functions (Gaussian, von Mises, hyperbolic secant, square hyperbolic secant, and Lorentz), it is found that the square hyperbolic secant function can best reproduce the profile, yielding an improved fit. Moreover, a symmetric 2D radiation beam function, instead of a simple 1D Gaussian function, is used to fit the profile. Each profile with either well-resolved or not-so-well-resolved peaks could be fitted adequately using this beam function, and the bridge emission between the two peaks does not need to be a new component. Adopting inclination and impact angles based on polarization measurements, the opening angle ({\theta}_{\mu}0) of the radiation beam in a certain frequency band is derived from beam-function fitting. The corresponding radiation altitudes are then calculated. Based on multi-frequency profiles, we also computed the Lorentz factors of the particles and their dispersion at those locations in both the curvature-radiation (CR) and inverse-Compton-scattering (ICS) models. We found that the Lorentz factors of the particles decrease rapidly as the radiation altitude increases. Besides, the radiation prefers to be generated in annular region rather than core region, and this needs further validation., Comment: 13 pages, 18 figures, ApJ, 816, 76

The inner annular gap (IAG), a new type of inner gap whose magnetic field lines intersect the null charge surface (NCS), is proposed to explain $\gamma$-ray and radio emission from pulsars. The IAG can be an important source for high-energy particles. The particles can radiate between the NCS and the IAG. Some observational characteristics in both $\gamma$-ray and radio bands, such as the $\gamma$-ray emission beams of Crab-like, Vela-like and Geminga-like, can be reproduced by numerical method. It is predicted that the view angle $\zeta$ should be larger than the inclination angle ($\zeta>\alpha$), otherwise the $\gamma$-ray radiation will have little possibility to be observed. Whether the inner annular gap (or cap) is sparking (or free flow) depends on the surface binding energy of the pulsar. In stead of neutron star models, the scenario of the IAG is favorable for bare strange star models, because bare strange stars can easily satisfy the requisite condition to form an IAG for both pulsars ($\vec{\Omega}\cdot \vec{B}0$)., Comment: ApJL, accepted

In a paper by Sanwal et al. (2002), it is supposed to be very difficult to interpret the absorption features in term of cyclotron lines. However, we would like to address here that the possibility of the absorption being cyclotron resonance can not be ruled out.We propose that the isolate neutron star, 1E 1207.4-5209 in the center of supernova remnant PKS 1209-51/52, has a debris disk and is in a propeller phase, with an accretion rate 6x10^{-11} M_solar/year., 4 page and 1 figure, revised substantially, or at http://vega.bac.pku.edu.cn/~rxxu/publications/index_P.htm

Pulsars provide unique probes of the large-scale interstellar magnetic field in the Galactic disk. Up to now, the limited Galactic distribution of the known pulsar population has restricted these investigations to within a few kiloparsec of the Sun. The Parkes multibeam pulsar survey has discovered many more-distant pulsars which enables us for the first time to explore the magnetic field in most of the nearby half of the Galactic disk. Here we report the detection of counterclockwise magnetic fields in the Norma spiral arm using pulsar rotation measures. The fields are coherent in direction over a linear scale of $\sim 5$ kpc along the arm and have a strength of $-4.4\pm0.9$ $\mu$G. The magnetic field between the Carina-Sagittarius and Crux-Scutum arms is confirmed to be coherent from $l\sim45\degr$ to $l\sim305\degr$ over a length of $\sim 10$ kpc. These results strengthen arguments for a bisymmetric spiral model for the field configuration in the Galactic disk., Comment: minor changes

Pulsar braking torques due to magnetodipole radiation and to unipolar generator are considered, which results in braking index being less than 3 and could be employed to test the emission models. Improved equations to obtain pulsar braking index and magnetic field are presented if we deem that the rotation energy loss rate equals to the sum of the dipole radiation energy loss rate and that of relativistic particles powered by unipolar generator. The magnetic field calculated by conventional way could be good enough but only modified by a factor of ~0.6 at most. Both inner and outer gaps may coexist in the magnetosphere of the Vela pulsar., A version with abbreviation, accepted by Astrophysical Journal Letters, http://vega.bac.pku.edu.cn/~rxxu/

During supernova explosions, strange stars with almost bare quark surfaces may be formed. Under certain conditions, these stars could be rapidly spun down by the torque exerted by the fossil disks formed from the fall-back materials. They may also receive large kicks and hence, have large proper motion velocities. When these strange stars pass through the spherical ``Oort'' comet cloud formed during the pre-supernova era, they will capture some small-scale comet clouds and collide with some comet-like objects occasionally. These impacts can account for the repeating bursts as observed from the soft gamma repeaters (SGRs). According to this picture, it is expected that SGR 1900+14 will become active again during 2004-2005., Comment: emulateapj, 5 pages, accepted by ApJ Letters

Some characteristics of the inverse Compton scattering (ICS) model are reviewed. At least the following properties of radio pulsars can be reproduced in the model: core or central emission beam, one or two hollow emission cones, different emission heights of these components, diverse pulse profiles at various frequencies, linear and circular polarization features of core and cones.

Qiao and his collaborators recently proposed an inverse Compton Scattering (ICS) model to explain radio emission of pulsars. In this paper, we investigate the polarization properties of pulsar emission in the model. First of all, using the lower frequency approximation, we derived the analytical amplitude of inverse Compton scattered wave of a single electron in strong magnetic field. We found that the out-going radio emission of a single relativistic electron scattering off the ``low frequency waves'' produced by gap-sparking should be linearly polarized and have no circular polarization at all. However, considering the coherency of the emission from a bunch of electrons, we found that the out-going radiation from the inner part of emission beam, i.e., that from the lower emission altitudes, prefers to have circular polarization. Computer simulations show that the polarization properties, such as the sense reversal of circular polarization near the pulse center, S-shape of position angle swing of the linear polarization, strong linear polarization in conal components, can be reproduced in the ICS model., Comment: 22 pages, 8 figures, LaTeX. ApJ (pt.1), accepted

Pulsars are among the most highly polarized sources in the universe. The NVSS has cataloged 2 million radio sources with linear polarization measurements, from which we have selected 253 sources, with polarization percentage greater than 25%, as targets for pulsar searches. We believe that such a sample is not biased by selection effects against ultra-short spin or orbit periods. Using the Parkes 64-m telescope, we conducted searches with sample intervals of 50 μs and 80 μs, sensitive to submillisecond pulsars. Unfortunately we did not find any new pulsars.

Pulsed gamma-ray emission from millisecond pulsars (MSPs) has been detected by the sensitive Fermi, which sheds light on studies of the emission region and mechanism. In particular, the specific patterns of radio and gamma-ray emission from PSR J0101-6422 challenge the popular pulsar models, e.g. outer gap and two-pole caustic (TPC) models. Using the three dimension (3D) annular gap model, we have jointly simulated radio and gamma-ray light curves for three representative MSPs (PSR J0034-0534, PSR J0101-6422 and PSR J0437-4715) with distinct radio phase lags and present the best simulated results for these MSPs, particularly for PSR J0101-6422 with complex radio and gamma-ray pulse profiles and for PSR J0437-4715 with a radio interpulse. It is found that both the gamma-ray and radio emission originate from the annular gap region located in only one magnetic pole, and the radio emission region is not primarily lower than the gamma-ray region in most cases. In addition, the annular gap model with a small magnetic inclination angle instead of "orthogonal rotator" can account for MSPs' radio interpulse with a large phase separation from the main pulse. The annular gap model is a self-consistent model not only for young pulsars but also MSPs, and multi-wavelength light curves can be fundamentally explained by this model., Comment: Accepted for publication in The Astrophysical Journal; 6 pages, 4 figures

We propose that the violent breakdown of the Ruderman-Sutherland type vacuum gap above the pulsar polar cap region may produce copious primary particles and make the charge density above the gap in excess of the Goldreich-Julian density. Such an excess residue of charge density may arise some re-acceleration regions above the gap due to the space-charge-limited flow mechanism. Such re-acceleration regions, if exist, may accelerate particles to carry away more spin-down energy, and may have some implications for pulsar $\gamma$-ray emission., Comment: 2 pages, no figures, LaTeX

There are three mechanisms to cause pulsar inner gap breakdown: the inverse Compton scattering (ICS) of the high energy particles off the thermal-peak photons, off the resonant-frequency photons and the curvature radiation (CR). The pulsar mode-changing phenomenon can be interpreted as a switching effect between theresonant ICS sparking modeand thethermal ICS sparking mode.

The discovery of the first known radio pulsar with a massive, nondegenerate companion is reported. PSR 1259-63, found during a large-scale high-frequency survey of the southern Galactic plane, has a period of 47 ms and a pulse profile similar to that of the Crab pulsar. Observations using the Parkes radio telescope at frequencies around 660 and 1520 MHz over the period 1989 November to 1991 September show that the pulsar is in a highly eccentric orbit around a massive companion. Near periastron, the pulsar is eclipsed, presumably by a wind from the companion star