Table of contents

This paper briefly introduces the past, present and future of pulsar studies in China.

This paper reports on the discovery of a new population of transient neutron stars. This new class of pulsars is characterized by quasi-periodic bursting with a non-radiating or `switched off' state, the duration of which exceeds the radiating `on' state. There are currently four such objects known, the prototype being the isolated pulsar B1931+24 (J1933+2421). This pulsar emits radio radiation for approximately 4–10 days before switching off completely for between 30–40 days, hence it is only visible for ∼ 10%−20% of the time. It is therefore concluded from simple calculations, that many more of these objects must exist and this will have large consequences for the population estimates of neutron stars in our Galaxy. Further studies will provide information about the conditions necessary for radio emission.

We carried out an analysis of the behaviour of individual pulses of PSR B0950+08 based on our observations at a frequency 111.2 MHz. The intensity and phase distribution of pulses at different longitudes of the pulsar average profile was investigated. The intensity of individual pulses can exceed ten times the average profile amplitude. It was shown that the intensity distribution of weak pulses with longitude of their appearance differs strongly from the distribution of strong pulses. The flux density of the average pulse changes by a factor of up to 13 from day to day, due to interstellar scintillation. It was shown that the cumulative distribution function is described by a polynomial fit of the second order in log-log scale.

We present the statistical results of a systematic, unbiased search for subpulse modulation of 187 pulsars performed with the Westerbork Synthesis Radio Telescope (WSRT) in the Netherlands at an observing wavelength of 21 cm (Weltevrede et al. 2006). We have increased the list of pulsars that show the drifting subpulse phenomenon by 42, indicating that more than 55% of the pulsars that show this phenomenon. The large number of new drifters we have found allows us, for the first time, to do meaningful statistics on the drifting phenomenon. We find that the drifting phenomenon is correlated with the pulsar age such that drifting is more likely to occur in older pulsars. Pulsars that drift more coherently seem to be older and have a lower modulation index. Contrary claims from older studies, both P₃ (the repetition period of the drifting subpulse pattern) and the drift direction are found to be uncorrelated with other pulsar parameters.

I review recent results concerning the shape of drifting subpulse patterns, and the relationship to model predictions. While a variety of theoretical models exist for drifting subpulses, observers typically think in terms of a spatio-temporal model of circulating beamlets. Assuming the model is correct, geometric parameters have been inferred and animated ``maps'' of the beam have been made. However, the model makes very specific predictions about the curvature of the drift bands that have remained largely untested. Work so far in this area indicates that drift bands tend not to follow the prediction, and in some cases discontinuities are seen that are suggestive of the superposition of out of phase drift patterns. Recent polarimetric observations also show that the drift patterns in the two orthogonal polarisation modes are offset in phase. In one case the pattern in one of the modes shows a discontinuity suggesting no less than three superposed, out-of-phase drift patterns! I advise caution in the interpretation of observational data in the context of overly simplistic models.

The well known drifter PSR B0031-07 is known to exhibit drifting sub-pulses where the spacing between the drift bands (P₃) shows three distinct modes A, B and C corresponding to 13, 7 and 4 times the pulsar period, respectively. We have investigated periodicities and polarisation properties of PSR B0031-07 for a sequence of 2700 single pulses taken simultaneously at 328 MHz and 4.85 GHz. We found that mode A occurs simultaneously at these frequencies, while modes B and C only occur at 328 MHz. However, when the pulsar is emitting in mode B at the lower frequency there is still emission at the higher frequency, hinting towards the presence of mode B emission at a weaker level. Further, we have established that modes A and B are associated with two orthogonal modes of polarisation, respectively. Based on these observations, we suggest a geometrical model where modes A and B at a given frequency are emitted in two concentric rings around the magnetic axis with mode B being nested inside mode A.

We report the detection of Giant Pulses (GPs) in the pulsar PSR J1752+2359. The energy of the strongest GP exceeds the energy of the average pulse by a factor of 200, in which it stands out from all known pulsars with GPs. PSR J1752+2359 as well as the previously detected PSR B0031–07 and PSR B1112+50, belongs to the first group of pulsars found to have GPs without a high magnetic field at the light cylinder.

A brief review of observational manifestation of pulsars with giant pulses radio emission, based on reference data and our detections of three new pulsars with giant pulses.

Evidence now exists that at least 14 pulsars emit distinctive pulses that are stronger and narrower than the average pulse. I review observations of these pulses in an effort to determine which sources share a common emission-mechanism. All of the giant pulses emitted by millisecond pulsars have power-law energy-statistics and occur in narrow phase-windows that coincide with those of X-ray emission. The giant pulses of millisecond pulsars therefore probably originate from a single process. They are always unresolved at microsecond timescales, and therefore the emission is likely to arise from the superposition of a small number of nano-shots. Most are actually very weak when compared to the average pulse. They are only ``giant'' when examined in terms of their ultra-high brightness temperatures. Giant pulses from other sources have a variety of widths, shapes, and energy distributions. The giant pulses from the Crab pulsar have intrinsic sub-microsecond timescales like the giant pulses of the millisecond pulsars, and therefore probably originate from the same mechanism. Other phenomena, such as giant micro-pulses from young pulsars and giant pulses from slow pulsars have not been shown to have such short timescales. These phenomena likely arise from other mechanisms.

We present the first direct evidence for turnover in pulsar radio spectra at high frequencies. New data for some pulsars, taken with the GMRT, show the maximum flux in the spectrum to be ∼ 1 GHz. We also find some evidence that this peak frequency of turnover in pulsar spectra appears to depend on dispersion measure and pulsar age.

A Pulsar coherent de-dispersion experiment has been carried out using the 25-m Nanshan radio telescope at Urumqi Observatory. It uses a dual polarization receiver operating at 18 cm and a VLBI back-end: Mark5A, the minimum sampling time is 5 ns. The data processing system is based on a C program on Linux and a 4-node Beowulf cluster. A high quality data acquisition system and a cluster with more processors are needed to build an on-line pulsar coherent de-dispersion system in future. The main directions for the instrument are studies of pulsar timing, scintillation monitoring, etc.

We update the systematic studies of circular polarization in integrated pulse profiles of Han et al. Sense reversal can occur in either core or cone components, or near the intersection between the components. The correlation between the sense of circular polarization and the sense of position angle variation for conal double pulsars is confirmed with a much larger database. Some pulsars show clear changes of circular polarization with frequency. Circular polarization is marginally different between millisecond and normal pulsars.

The Parkes Multibeam Survey led to the identification of a number of long-period radio pulsars with magnetic field well above the `quantum critical field' of ∼4.4×10¹³ G (HBRPs). Traditional pulsar emission theories postulate that radio emission is suppressed above this critical field. The aim of this project is to understand emission properties of HBRPs.

We monitored PSR B0329+54 for four months using the Nanshan 25-m radio telescope at 1540 MHz. The observations reveal three mode changing events, that lasted for 37, 12 and 17 min respectively. The integrated flux densities for the different observations differ greatly from their average value. The modulation indices of individual observations vary in a wide range as well, indicating that the intrinsic flux density is largely modulated by the scintillation effect.

Observations of AXP 1E 2259+586 and XDINS 1RXS J1308.6+212708 at 111, 87, 61 and 42 MHz are reported. Mean pulse profiles, as well as, the estimation of the dispersion measures, distances, spectral indices, and integrated radio luminosities of both objects are presented. Comparison with X-ray data shows large differences in the mean pulse widths and luminosities. The detection of radio emission from these two X-ray pulsars, together with other data, suggests the need to revise the radio-emission mechanisms in the magnetar model or the magnetar model itself.

A generic interpretation of pulsar radio emission that does not rely on the identification of a specific emission mechanism is explored. Coherence is quantified in terms of a coherence factor, which implies a maximum brightness temperature; the possible significance of Poincaré invariants is pointed out, and the potential use of higher order moments of the intensity to measure the coherence is discussed. The effect of the Lorentz boost between the plasma rest frame and the pulsar frame, the suppression of emission at low frequencies due to curvature of the field lines, and a natural frequency of the pulsar plasma are incorporated into a generic model for pulsar emission, and three illustrative examples of its possible use are given.

We discuss a possible scenario that allows explanation of the anti-correlation between MP sand IP of PSR B1822–09. We assume that the working regime of the inner gap is influenced by the outer gap. Depending on the surface temperature of the polar cap, one can expect alteration of the mean Lorentz factors of the secondary particles, which drastically affects the radio emission process. We also propose the model of generation of the coherent radio emission in reversible direction, toward the neutron star. The model is based on the resonant interaction of plasma clouds, created by gamma rays radiated in inner and outer gaps.

We discuss observational facts that can be interpreted in terms of inward emission in pulsar magnetosphere. These include the main-pulse/interpulse anticorrelation in B1822-09 and the locations of emission and absorption features in the pulse profile of B0950+08. Weaknesses of geometrical models employing the inward emission are carefully discussed.

The origin of pulsar radio emission has been a mystery for more than 35 years. The observed extremely high brightness temperatures strongly suggest that the radio emission must be highly coherent, but the real mechanism in operation has been evading identification. Instead of trying to solve this decades long problem, here I discuss several recent new observations and the ideas to interpret them, which shed new light on understanding pulsar radio emission. The topics include (1) a recent XMM-Newton observation of the famous, old-drifting PSR B0943+10 and its physical implications; (2) models to interpret the radio flaring activity of the pulsar B in the double pulsar system PSR J0737–3099; (3) possible identification of the inward radio emission from some pulsars; and (4) the suggestion that GCRT J1745–3009 is a white dwarf pulsar. Two possible interpretations to the recently identified Rotating RAdio Transients (RRATs) are also proposed.

Our recent studies of pulsar population statistics suggest that improvements of radio and gamma-ray beam geometry and luminosity models require further refinement. The goal of this project is to constrain the viewing geometry for some radio pulsars, especially three-peaked pulse profiles, in order to limit the uncertainty of the magnetic inclination and impact angles. We perform fits of the pulse profile and position angle sweep of radio pulsars for the available frequencies. We assume a single core and conal beams described by Gaussians. We incorporate three different size cones with frequency dependence from the work of Mitra & Deshpande (1999). We obtain separate spectral indices for the core and cone beams and explore the trends of the ratio of core to cone peak fluxes. This ratio is observed to have some dependence with period. However, we cannot establish the suggested functional form of this ratio as indicated by the work of Arzoumanian, Chernoff & Cordes (2002).

The problem of formation of a partially screened inner acceleration region for 102 pulsars with drifting subpulses is considered. It is argued by means of the condition T_c/T_s>1 (where T_c is the critical temperature above which the surface delivers thermal flow at the corotation limited level and T_s is the actual surface temperature) that an efficient acceleration region can be formed in a very strong and curved, non-dipolar surface magnetic field, even exceeding 10¹⁴ G in general. Both positively and negatively charged polar caps are considered. Also, both curvature radiation as well as resonant inverse Compton radiation seed photons are taken into account. It is argued that the former mechanism is much more likely to account for the sparking discharge of the partially screened inner acceleration region in pulsars.

Formation of giant radio pulses is attributed to propagation effects in the plasma of pulsar magnetosphere. Induced scattering of radio waves by the plasma particles is found to lead to an efficient redistribution of the radio emission in frequency. With the steep spectrum of pulsar radiation, intensity transfer between the widely spaced frequencies may imply significant narrow-band amplification of the radiation. This may give rise to giant pulses. It is demonstrated that the statistics of giant pulse intensities observed can be reproduced if one take into account pulse-to-pulse fluctuations of the plasma number density and the original intensity. Polarization properties of the strongly amplified pulses, their location in the average pulse window and the origin of the nanostructure of giant pulses are discussed as well.

Geometrical properties of the annular gap model, efforts of observational tests on it and applications of the model to explain the bi-drifting phenomenon are introduced in this paper. It was shown that in the frame of the annular gap model the observed γ-ray and radio radiation properties of pulsars can be well reproduced. The annular gap model can naturally explain the bi-drifting phenomenon, which is difficult to be understood in classical inner vacuum models. Recently, Wang et al. proposed an independent geometrical method to determine the location for the multi-band radiation regions of PSR B1055–52. They found that the γ-ray emission and radio main pulse emission come from the annular gap, while the radio inter-pulse originates from the core cap region. The results show that the constrained radio and γ-ray emission regions are generally consistent with the predictions of the annular gap model.

Polarization evolution of radio waves in the plasma of pulsar magnetosphere is considered. The polarization state of the natural waves linearly polarized in orthogonal directions is found to change considerably because of the wave mode coupling and the cyclotron aborption. It is shown that the original natural waves acquire elliptical polarization and become slightly non-orthogonal. A model of the individual pulse polarization is suggested based on an idea of fluctuations in the plasma flow. The implications of the individual pulse polarization data for diagnostics of pulsar plasma are outlined as well.

The rapidly spinning pulsars could be regarded as the consequence of a competition between gravitational wave emission and viscous dissipation. All cases, neutron stars, strange stars and hybrid stars, are discussed here. Viscosity due to strangeness-changing weak interactions in dense nuclear matter fixes the fastest spinning frequency. This only implies the existence of strangeness in the interior of the stars, and does not distinguish among hyperon matter, strange quark matter or a mixture of the two. We conclude that the cluster of rapidly spinning pulsars, containing two fastest millisecond pulsars and low-mass X-ray binaries, is possibly signalling strangeness.

A geometric method that attempts to synthesize all available geometric information on a pulsar is developed to constrain the 3-D structure of emission regions of pulsars. In terms of retarded magnetic dipolar field and with inclusion of aberration and retardation effects, the method is endeavored to constrain the geometrical parameters of emission regions via reproducing observational multi-wavelength features, e.g. pulse widths, phase offsets between different pulses and polarization properties. It is applied to gamma-ray pulsar B1055–52 which shows main pulse and inter-pulse at radio frequencies and double-peaked light curve at gamma-ray energy band. The results imply that the radio emission region probably consists of an inner and an outer ring, while the gamma-ray emission region is severely asymmetrical to magnetic axis.

Given sufficient sensitivity, pulsar timing observations can make a direct detection of gravitational waves passing over the Earth. Pulsar timing is most sensitive to gravitational waves with frequencies in the nanoHertz region, with the most likely astronomical sources being binary super-massive black holes in galaxy cores. The Parkes Pulsar Timing Array project uses the Parkes 64-m radio telescope to make precision timing observations of a sample of about 20 millisecond pulsars with a principal goal of making a direct detection of gravitational waves. Observations commenced about one year ago and so far sub-microsecond timing residuals have been achieved for more than half of these pulsars. New receiver and software systems are being developed with the aim of reducing these residuals to the level believed necessary for a positive detection of gravitational waves.

Pulsar timing of millisecond pulsars are carried on at Kalyazin radio astronomical observatory (Russia) since 1995. Seven pulsars are observed at 0.6 GHz by full steerable 64-m dish radio telescope RT-64 and filter-bank receiver. The millisecond pulsar B1937+21 is being monitored at Kalyazin observatory (0.6 GHz) and Kashima space research centre of NICT (Japan) (2.3 GHz), simultaneously since 1996.

An algorithm of the ensemble pulsar time based on the Wiener filtration method has been constructed. This algorithm has allowed the separation of the contributions of an atomic clock and a pulsar itself to the post-fit pulsar timing residuals. The method has been applied to the timing data of the millisecond pulsars PSR B1855+09 and PSR B1937+21 and allowed to filter out the atomic scale component from the pulsar phase variations. Direct comparison of the terrestrial time TT(BIPM96) and the ensemble pulsar time PT_ens has displayed that the difference TT(BIPM96) – PT_ens is within ±0.4 μs range. A new limit of gravitational wave background based on the difference TT(BIPM96) – PT_ens was established to be Ω_gh²∼10⁻¹⁰.

J0737-3039 is the recently-discovered, first-known double-pulsar binary, a very compact double neutron star system in which both stars are observable as radio pulsars. In this review, we briefly describe the discovery and the studies which have been enabled by the unique properties of the system. These range from the most precise confirmation yet of the theory of general relativity, with the possibility of even more new tests and the measurement of second-order post-Newtonian effects, to studies of the magnetospheres and emission properties of the two pulsars. The discovery also resulted in a significant increase in the expected rate of occurrence of the mergers of double neutron star systems, and hence the likely rate of detection of such events by the new ground-based gravitational wave detectors.

Pulsar timing techniques allow a pulsar's rotational, astrometric and binary parameters to be measured to high precision. Any features that remain in the timing residuals after fitting for the expected pulsar parameters are suggestive of unmodelled physics such as binary companions, free precession or glitch events. In this paper we provide an overview of the features observed in the timing residuals that collectively are referred to as ``pulsar timing noise''. We use results obtained from the literature and from the Jodrell Bank observatory archive of timing residuals.

The Parkes Globular Cluster survey at 1.4 GHz has found so far twelve recycled pulsars in six globular clusters. Timing of these sources as well as follow-up observations at other electro-magnetic bands are providing a wealth of interesting results, which are summarized here.

We report on recent pulsar timing observations undertaken by the Urumqi Observatory. Observations for 74 radio pulsars have been made regularly at an observing frequency of 1540 MHz as part of the Urumqi Observatory timing program, which commenced in 1999 November at the 25-m Urumqi Nanshan telescope. Currently 284 pulsars are monitored with an average interval between observations of ∼9 days. The dedispersion is provided by a 2×128×2.5 MHz filterbank/digitiser system. Accurate and updated periods, period derivatives and positions have been obtained for the majority of the 74 pulsars with timing observations spanning more than one year. For datasets spanning more than one year we have obtained improved positions, proper motions and velocities. Comparing our measurements of period and period derivative with earlier observations, we conclude that, long-term period and period-derivative fluctuations may be dominated by unseen glitches. We also present the observed results for ten glitches of four young pulsars detected in the last five years.

Many systematic effects need to be removed in order to obtain the highest quality pulsar timing data. Interstellar propagation effects may be reduced by employing coherent dedispersion and observing at 1 GHz or above to avoid strong scattering. However, these techniques may not adequately bring propagation effects below the level of other systematic or random errors in the observation. We show that low-level scattering in a Kolmogorov halo produces time delays that are much larger than normally recognized and are time variable. These may be a significant source of noise in some high precision timing efforts.

TEMPO2 is a new pulsar timing package that provides the precision necessary for modern millisecond timing projects and should supersede all existing pulsar timing packages such as TEMPO and PSRTIME. As TEMPO2 is the only program available that can analyse multiple pulsar datasets simultaneously it will become an integral part of pulsar timing array projects which aim to detect the signatures of gravitational radiation in pulsar timing residuals. In this paper we describe the basic functionality of TEMPO2.

Several radio pulsars have now been shown to emit giant pulses that align in phase with high energy emission rather than with their integrated pulse components. We investigate whether timing of giant and γ-ray pulses can be used to improve limits on the energy scale of quantum gravity by placing bounds on the energy dependence of the speed of light. We find good sources for this experiment are putative Crab-like pulsars in M31, which should in principle be detectable by the current generation of radio telescopes. However, the detection of pulsed emission from theirγ-ray counterparts seems unlikely in the near future.

Pulsar observers have to contend with several effects of propagation through the ionized interstellar medium. I review those effects and how they can be used to study the interstellar plasma. Pulsars are normally observed under conditions of strong scintillation and show both diffractive and refractive effects. I emphasize the diffractive scintillation as exhibited in the dynamic spectrum and in its converse – pulse broadening. From Parkes observations of the pulse broadening of PSR J1644-45, I estimate the inner scale in an interstellar region of strong plasma turbulence to be about 100 km. I discuss the representation of dynamic spectra in terms of their ``secondary spectra'' and show how the arcs, that are often revealed, are related to both angular broadening and pulse broadening. Anisotropy in the scattering both changes the scattered pulse shape but also enhances the visibility of the arcs.

Multi-path scattering through inhomogeneities in the interstellar medium causes many related effects. In this review, I concentrate on the phenomenon of scintillation arcs, which are parabolic patterns in the secondary spectrum caused by interference between different angular components of the scatter-broadened image of a pulsar. Scintillation arcs are now fairly well understood. The measured curvature of the arc, together with proper motion and distance information about the pulsar, can be used to determine the location of thin scattering screens along the line of sight to the object. Some recent work of this type is presented. The puzzle of substructure in the power distribution of scintillation arcs is poorly understood, however, and is commented on as an open puzzle. In particular, some inferred physical structures in the ISM are small scale (∼ 1 AU) and over-dense with respect to the background medium. Finally, an application of scintillation arc studies to the correction of high-precision pulsar timing is presented.

A decade ago, there was very limited knowledge of magnetic fields of our Galaxy. The local fields in the Solar vicinity were known to be directed towards a Galactic longitude l∼ 90° with reversed directions at smaller Galacto-radii. The regular field strength was found to be about 2 μG. The filaments near the Galactic Center show the possible poloidal fields there. There was no information about the magnetic fields in the Galactic halo. In last decade, there has been significant progress on measurements of the Galactic magnetic fields. In the Galactic disk, from the RMs of a large number of newly observed pulsars, large-scale magnetic fields along the spiral arms have been delineated in a much larger region then ever before, with alternating directions in the arm and interarm regions. The toroidal fields in the Galactic halo have been revealed to have opposite directions below and above the Galactic plane, which is an indication of an A0 mode dynamo operating in the halo. The strength of large-scale fields also has been found from pulsar RM data to exponentially increase at smaller Galacto-radii. Compared to the steep Kolmogorov spectrum of magnetic energy at small scales, the large-scale magnetic fields show a shallow broken spatial magnetic energy spectrum.

We present the results from a novel experiment for accurate estimation of pulsar dispersion measure (1 part in 10⁴) using the GMRT, without requiring any absolute timing information. The observations were carried out over a period of more than one year for a sample of twelve pulsars. We have used the simultaneous multi-frequency capability of the GMRT. Most of the sample pulsars studied show dispersion measure (DM) variations on time scales of weeks to months. The mean DM value for some of the pulsars show a significant discrepancy with respect to the catalog value. Pulsar B2217+47 shows a large-scale DM gradient over a one year period. For some pulsars we find small differences in the DM values obtained from different frequency combinations.

The stationary phase point (SPP) method is introduced to treat the diffractive scintillation. From weak scattering, where the SPP number N = 1, to strong scattering (N>>1), via transitional scattering regime (N∼2, 3), we find that the modulation index of intensity experiences the monotonically increasing from 0 to 1 with the scattering strength, characterized by the ratio of Fresnel scale r_F to diffractive scale r_diff.

Low-frequency waves and energy dissipation in the relativistic pulsar wind are discussed. The Poynting flux, which is initially dominant in the pulsar wind, may be transported by large amplitude low-frequency waves: in the region near the pulsar such waves can be relativistic MHD waves, and in the region far from the pulsar they can be electromagnetic (EM) waves. Both types of wave are considered and in the latter case, coherent nonlinear Compton scattering may lead to highly beamed coherent radio emission with synchrotron-like spectra, which may be potentially observable.

Low-intensity scattering in discrete screens gives rise to parabolic scintillation arcs in pulsar secondary spectra. The curvature of the arc boundary is uniquely determined by the location of the screen along the line of sight, the distance to the pulsar, and the relative velocity of pulsar and Earth (assuming the transverse screen velocity to be small). This information is usually available for the strong pulsars needed to exhibit clear scintillation arcs. Early studies reported single arcs along most lines of sight. This seemed puzzling given the variety of distances and sight lines being probed. We report new, higher sensitivity observations that show up to four scintillation arcs for a particular sight line.

We review our case for strong observational evidence for a relationship between the direction of a pulsar's motion and its rotation axis. The information comes from calibrated polarization data for 20 pulsars which display linearly polarized emission from the pulse longitude at closest approach to the magnetic pole. Of these 20 pulsars, 10 show an offset in the angle between the velocity vector and the polarisation position angle which is either less than 10° or more than 80°, a fraction which is very unlikely by random chance. We believe that the bimodal nature of the distribution arises from the presence of orthogonal polarisation modes in the pulsar radio emission. In some cases this orthogonal ambiguity is resolved by observations at other wavelengths so that we conclude that the velocity vector and the rotation axis are aligned at birth. Strengthening the case is the fact that 4 of the 5 pulsars with ages less than 3 Myr show this relationship, including the Vela pulsar.

Observations over the last decade have shown that neutron stars (NSs) receive a kick velocity (of order a hundred to a thousand km s⁻¹) at birth. The physical origin of the kicks and the related supernova asymmetry is an unsolved problem. We study observational constraints on kicks for isolated pulsars and for neutron stars in binary systems. For several young pulsars, X-ray observations of compact nebulae showed that pulsar proper motion is aligned with the spin direction as defined by the symmetry axis of the nebula. Such alignment is also seen from a new analysis of radio polarization data for a large number of pulsars. On the other hand, for various NS binaries (including double NS systems, binaries with massive main-sequence star companion and binaries with massive white-dwarf companion), we find that the kick velocity is misaligned with the the NS spin axis in a number of systems, and the NS spin period (when available) in these systems is generally longer than several hundreds milliseconds. These observational constraints suggest that the kick timescale is hundreds of milliseconds to 1s, so that spin-kick alignment or misalignment can be obtained depending on the initial spin period of the NS. We discuss the implication of our result for various NS kick mechanisms.

We estimate the strength of the induced magnetic field due to the Pauli paramagnetic moment of the ³P₂ Cooper pairs for the anisotropic (³P₂) neutron superfluid under the applied magnetic field (B₀) in neutron stars. The induced magnetic field of the anisotropic (³P₂) neutron superfluid is as follows. B⁽ⁱⁿ⁾≈(1.9/T₇)ηB₀ (T₇ denotes the interior temperature of the neutron star in unit of 10⁷ K), η = (m(³P₂)/0.1 M_⊙)R_NS,6⁻³. The induced magnetic field will gradually increase with the temperature of the neutron star decreasing in their late evolutionary stage. A magnetar may appear in a condition when T₇<<η. The upper limit of the magnetic field for the magnetars is B_max⁽ⁱⁿ⁾(³P₂)≈2.02×10¹⁴η.

Escape of the trapped neutrinos from a protoneutron star might cause a phase transition from a core nucleonic neutron star to a core hyperonic neutron star, which leads to the softening of the equation of state. We study the effects of the phase transition on the rotational evolution of a protoneutron star. It is found that the star keeps shrinking and spinning up until all the trapped neutrinos escape. If the hyperonic star is metastable, its rotational frequency accelerates distinguishedly before it collapses to a black hole.

We study the γ-ray emission from the pulsar magnetosphere based on outer gap models, and the TeV radiation from pulsar wind nebulae (PWNe) through inverse Compton scattering using a one-zone model. We carry out Monte Carlo simulations of γ-ray pulsars in the Galaxy and the Gould Belt, assuming values for the pulsar birth rate, initial position, proper motion velocity, period, and magnetic field distribution and evolution based on observational statistics. We select from the simulation a sample of 44 mature pulsars in the Galactic plane (|b|⩽5°) and a sample of 32 mature pulsars at high latitudes (|b|>5°) which could be detected by EGRET. About 12 mature pulsar could be observed in the radio band. The results showed that GeV radiation from the magnetosphere of mature pulsars can contribute to the high latitude unidentified EGRET sources. The TeV fluxes from the pulsar wind nebulae of our simulated sample produced through inverse Compton scattering by relativistic electrons on the cosmic microwave background and synchrotron seed photons are calculated. We suggest that strong EGRET sources may be potential TeV source candidates, and up to 15 sources could be detected by present and future three-generation TeV telescopes if they are mature pulsars.

A brief review of known models for the description of Anomalous X-ray Pulsars (AXPs) and Soft Gamma-Repeaters (SGRs) is given. A new model is proposed to explain the main properties of these objects and radio pulsars with long periods on the base of the conception of drift waves in the vicinity of the light cylinder of the neutron star with the surface magnetic field ∼10¹² G.

We propose that there possibly exists a population of millisecond pulsars in the Galactic center region. Millisecond pulsars (MSPs) could emit GeV gamma-rays through synchrotron-curvature radiation as predicted by outer gap models. In the same time, the compact wind nebulae around millisecond pulsars can emit X-rays though synchrotron radiation and TeV photons through inverse Compton processes. Besides, millisecond pulsar winds provide good candidates for the electron-positrons sources in the Galactic center. Therefore, we suggest that the millisecond pulsar population could contribute to the weak unidentified Chandra X-ray sources, the diffuse gamma-rays detected by EGRET, electron-positron annihilation lines and possible TeV photons detected by HESS toward the Galactic center.

Unexpected sign, significant magnitude and variable frequency second derivative exists not only in singular radio pulsars but also in Soft Gamma repeaters (SGRs) and Anomalous X-ray pulsars (AXPs). This paper shows that these phenomena are related, and can be interpreted by a simple unified model, long-term orbital effect. Thus many of previous ``isolated'' pulsars may be binary pulsars, i.e., orbital periodP_b≈(47,72)min for AXP 1E 2259+586, and P_b≈(20,34)min for PSR J1614–5047, P_b≈(3.6,6.4)min for SGR 1900+14, and P_b≈(1.5,5.8)min for SGR 1806–20. In this model, the frequency first derivative of these pulsars is still dominated by magnetic dipole radiation. Therefore, it is not contradictory to the magnetar interpretation of SGRs and AXPs. In other words, the model of this paper provides new interpretation to higher order of derivatives of pulse frequency (second and third...) instead of the first.

Members of the family of pulsar-like stars are distinguished by their different manifestations observed, i.e., radio pulsars, accretion-driven X-ray pulsars, X-ray bursts, anomalous X-ray pulsars/soft gamma-ray repeaters, certral compact objects, and dim thermal neutron stars. Though one may conventionally think that these stars are normal neutron stars, it is still an open issue whether they are actually neutron stars or quark stars, as no convincing work, either theoretical from first principles or observational, has confirmed Baade-Zwicky's original idea that supernovae produce neutron stars. After introducing briefly the history of pulsars and quark stars, the author summarizes the recent achievements in his pulsar group, including quark matter phenomenology at low temperature, starquakes of solid pulsars, low-mass quark stars, and the pulsar magnetospheric activities.

An aligned pulsar whose rotation axis and magnetic dipole axis are parallel should be positively charged. We consider the electromagnetic field both inside and outside the star under a specific condition and derive the total charge of a pulsar. The statistical relation between the pulsar's rotation energy loss rate (or the period derivative) and the period may imply that the millisecond radio pulsars with small periods could be low-mass bare strange stars.

Based on the undisturbed finitely thick disk gravitational potential, 3-D trajectories of pulsars are followed with initial locations and velocities randomly selected from a model distribution. Three typical instances are followed for some 10¹¹ yr, and their Poincaré sections are used as diagnostics of their motion. We find that the vertical-to-parallel range ratio (relative to the Galactic plane) to be an important parameter: as this ratio increases, the pulsar's motion changes from being regular to being irregular/chaotic.

Since mid-2005, a pulsar searching system has been operating at 18 cm on the 25-m radio telescope of Urumqi Observatory. Test observations on known pulsars show that the system can perform the intended task. The prospect of using this system to observe 3EG sources and other target searching tasks is discussed.

The timing of radio pulsars provides a tool for studying a wide range of fundamental physical and astrophysical problems. The best results are obtained by regular, frequent timing observations of a large number of sources at various frequencies. We describe a project which aims to improve on all of the above parameters by combining timing data from the pulsar timing programs of 4 European groups to form the so-called EPTA. These data will be used to study, amongst other things, relativistic binaries and gravitational waves.

FAST, Five hundred meter Aperture Spherical Telescope, is the Chinese effort for the international project SKA, Square Kilometer Array. An innovative engineering concept and design pave a new road to realizing huge single dish in the most effective way. Three outstanding features of the telescope are the unique karst depressions as the sites, the active main reflector which corrects spherical aberration on the ground to achieve full polarization and wide band without involving complex feed system, and the light focus cabin driven by cables and servomechanism plus a parallel robot as secondary adjustable system to carry the most precise parts of the receivers. Besides a general coverage of those critical technologies involved in FAST concept, the progresses in demonstrating model being constructed at the Miyun Radio Observatory of the NAOC is introduced. Being the most sensitive radio telescope, FAST will enable astronomers to jumpstart many of science goals, for example, the natural hydrogen line surveying in distant galaxies, looking for the first generation of shining objects, hearing the possible signal from other civilizations, etc. Among these subjects, the most striking one could be pulsar study. Large scale survey by FAST will not only improve the statistics of the pulsar population, but also may offer us a good fortune to pick up more of the most exotic, even unknown types like a sub-millisecond pulsar or a neutron star – black hole binary as the telescope is put into operation.

The recently started Arecibo L-band Feed Array (ALFA) pulsar survey aims to find ∼1000 new pulsars. Due to its high time and frequency resolution the survey is especially sensitive to millisecond pulsars, which have the potential to test gravitational theories, detect gravitational waves and probe the neutron-star equation of state. Here we report the results of our preliminary analysis: in the first months we have discovered 21 new pulsars. One of these, PSR J1906+0746, is a young 144-ms pulsar in a highly relativistic 3.98-hr low-eccentricity orbit. The 2.61±0.02 M_⊙ system is expected to coalesce in ∼300 Myr and contributes significantly to the computed cosmic inspiral rate of compact binary systems.

The National Astronomical Observatories, Chinese Academy of Sciences is now building a 50 m radio telescope at the Miyun Station. In this paper, we give a brief introduction to the Miyun Station. The main specifications and the status of construction of the 50 m radio telescope are described. We are now building an L-band pulsar receiver for this new 50 m telescope. The status of this receiver project is also described. The 50 m telescope, together with the pulsar receiver, will make it a powerful radio telescope to carry out pulsar observations and researches in the near future.

A radio telescope of 50m in diameter, basically, for pulsar observation, is to work at multi-wave bands among which the shortest wavelength is 13 cm. Proposed is a fully steerable exposed truss structure scheme of the telescope. The design is essentially a wheel-on-track style radio telescope with 6 rollers in three bodies for azimuth drive and support, while two sets of gear wheel for elevation drive. The main reflector is a mesh with crimped stainless steel wire spanned on a ``bowl-like'' back-up truss structure which is supported by 6 points on its bottom. After discussion of structural design and related dead-load analysis, wind and thermal disturbances are estimated. Particularly, response spectrum seismic hazard is performed with response spectra analysis. The results confirm that the 50m radio telescope can meet the observational requirements and survive seismic hazard of acceleration of 0.1 gravity with a light and cost-effective structure.

A new kind of position control system for basic elements of sphere is introduced in the paper. Based on mechanical principle, structure analysis is made for the control system, which proved that it meets special need of the position control system of FAST (Five-hundred-meter Aperture Spherical Telescope). In addition, kinematics analysis is made for the compensation fit of the system and compensating size is calculated. Lastly, some results of experiment are given.

In this work, using the data base at the University of Michigan Radio Astronomy Observatory (UMRAO) at 8 GHz, we investigated the possible periodicity in the radio light curves using Jurkevich analysis method. The results show that the radio sources display a possibly physically significant periodicity in a range of 0.08 to 14.5 years. Besides, the radio spectral indexes are also calculated, the results show that the averaged radio spectral index is α_4.8^14.5 = −0.15 (f_ν∝ν^α) for flat spectrum radio quasars (FSRQs) and α_4.8^14.5=0.01 for BL Lacertae objects. Some discussions are included.

We present the results of intraday variability observations in compact extragalactic radio sources with the 25 m radio telescope of Urumqi Astronomical Observatory at 5 GHz. In total we have observed 116 flat-spectrum sources, of these, 17 show IDV. We present here a summary table of the results, as well as the light curves and structure functions of a few sources. Either interstellar scintillation or an intrinsic origin could be the cause of the variability in these IDV sources. Further observations over a longer time scale are needed to explain the IDV.

Based on a sample of 69 blazars, relationships between flux density and spectral index, and distributions of redshift and spectral index have been investigated for highly frequency peaked BL Lac (HBLs), lowly frequency peaked BL Lac (LBLs) and flat spectrum radio quasars (FSRQs) respectively. Our result shows that (1) an anti-correlation between flux density and spectral index is found for HBLs, there is no clear relation for LBLs or FSRQs, which suggest that the X-ray emission in HBLs are from synchrotron process while that for LBLs and FSRQs from synchrotron self-Compton process, (2) the X-ray spectral index has a consequence for the three subclasses with HBLs showing the softest X-ray spectrum and FSRQs the hardest X-ray spectrum and with LBLs the middle of HBLs and FSRQs.

A long-term monitoring of 13 Be/X-ray binaries and 34 Be stars have been carried out with the 1.26 m reflector and the 2.16 m telescope at Xinglong Station. The observations cover the period of about 13 years in the optical spectroscopy and about 5 years in the near-infrared photometry. We present the monitoring results of two sources, X Persei and LSI +65°010, in the program. We detect changes of Hα EWs and JHK magnitudes in X Persei which reflect the formation of the extensive and dense envelope. The JHK magnitudes increase and decay rapidly while the variation of the Hα is wild. The behavior is suggestive of the envelope with different optical depth. The red-shift component in LSI +65°010 have been found in the monitoring program. The component may be brought from the neutron star with the movement in the line of sight.

Based on the beaming model, a relation between the observed polarization and Doppler factor was obtained for BL Lacertae objects–BLs. If the flat spectral radio quasars—FSRQs fit a similar polarization-Doppler factor relation as BL Lacs, then we can find that the ratio, f, of the de-beamed jet luminosity to the unbeamed luminosity in the source frame in BLs is greater than that in FSRQs. In addition, in a revised polarization and core-dominance parameter plot, they obey to differently linear correlation suggesting that they have some differently intrinsic properties. The difference in f, found here, is consistent with the result by Fan (2003), which perhaps account for the emission line difference between BLs and FSRQs. We proposed that there is no evolution between BLs and FSRQs and their emission line difference is from the difference in their ratio f.

A method to find the ``true'' Fourier spectrum for unevenly spaced time series is developed. It is found that the ``true'' Fourier spectrum associates with the conventional Fourier spectrum by a system of linear equations, so the ``true'' Fourier spectrum can be obtained by any methods of solving the system of linear equations (here the method of iterative process is choosed). It is an effective method for detecting and describing the ``true'' multiperiodic signals, even in the case where some strong peaks in a conventional Fourier spectrum occur at spurious frequencies. For the ``true'' Fourier spectrum composed of finite isolated harmonic components, this method gives a better estimation of the frequencies and amplitudes. This method is tested using simulated time series and the published data for servel blazars. Then it is applied to some radio variabilities of a sample of blazars. In some cases, typical timescales of several decades are found, indicating that this method is capable of finding very low frequency signals.

In this work, we revisit the unification scheme using the radio observations of X-ray selected BL Lacertae objects (XBLs) and FRI radio galaxies. The results are: 1) BL Lacertae objects and FRI radio galaxies show similar extended radio luminosity, and 2) In the luminosity and core-dominance plot, BL Lacertae objects and FRI radio galaxies are located in the same region, suggesting a unification of XBLs and FRI radio galaxies.