Wu Xin-ji

Is there evidence for torsion

Under the assumption of a pulsars magnetic field originating from the net polarized spin of its neutrons, and by using the post-Newtonian approximated torsion in the fifth order in (v/c), the spin precession arising from torsion is coordinate dependent, which influences the magnetic field of the pulsar and makes the magnetic inclination close to the rotation axis. Assuming the possibility of the magnetic inclination density to be in random alignment at the initial time, our theoretical calculations show that most pulsars should have smaller inclinations at the age of 106-107 yr, and that the inclination decreases with the increasing age of the pulsar. This fits the theoretical calculations and astronomically observed distribution.Under the assumption of a pulsars magnetic field originating from the net polarized spin of its neutrons, and by using the post-Newtonian approximated torsion in the fifth order in (v/c), the spin precession arising from torsion is coordinate dependent, which influences the magnetic field of the pulsar and makes the magnetic inclination close to the rotation axis. Assuming the possibility of the magnetic inclination density to be in random alignment at the initial time, our theoretical calculations show that most pulsars should have smaller inclinations at the age of 106-107 yr, and that the inclination decreases with the increasing age of the pulsar. This fits the theoretical calculations and astronomically observed distribution.

Refractive Interstellar Scintillation for Flux Density Variations of Two Pulsars

The flux density structure functions of PSRs B0525+21 and B2111+46 are calculated with the refractive interstellar scintillation (RISS) theory. The theoretical curves are in good agreement with observations [Astrophys. J. 539 (2000) 300] (hereafter S2000). The spectra of the electron density fluctuations both are of Kolmogorov spectra. We suggest that the flux density variations observed for these two pulsars are attributed to refractive interstellar scintillation, not to intrinsic variability.

A COLLECTIVE RADIATION MECHANISM FOR THE CORE EMISSION OF PULSARS

In the magnetic axial ambience of the rapidly rotating pulsar, the position beam has been accelerated by the gap of the intense electric field, and ejected with rotation around the magnetic axis. While there exists rare plasma envelope near the pulsar, such energetic and rotational positron beam may have those waves near the ion-cyclotron frequencies amplified in the direction of the magnetic field, by exciting Čerenkov and maser instabilities. These are a kind of coherence radiation which has a larger portion of circular polarization. Under this mechanism, the emerging of another radiation process from the pulsars, that is, the core emission can be satisfactorily explained. This paper also discusses some possible observations resulting from the mechanism.

RELATIONSHIPS BETWEEN LOBE STRUCTURE AND TOTAL LUMINOSITY OF RADIO-SOURCES

Abstract We made a statistical analysis using the Cambridge 5km, 5 GHz data on double radio sources and found highly significant correlations between the following pairs of parameters; the energies in the hot spots and the extended regions, Eh and Ee; their luminosities, Lh and Le; energy density in the hot spots K and the total luminosity Lt and the ratio of energy densities K A and Lt. These correlations exemplify the role of the hot spots in the radio sources.

Accumulation and release of energy near the light cylinder of a neutron star

Abstract We point out that high-energy particle bunches are produced by magnetic annihilation near the light cylinder and hence the pulsed radiation from a neutron star. More explicitly: (1) Magnetic energy may accumulate very rapidly owing to the differential rotation in the non-corotating region near the light cylinder of a neutron star. The scale of the accumulating region is consistent with the observed scale. (2) In a steady-state, the energy is released at the same rate as it is accumulated. We envisage the release to be accomplished by magnetic annihilation. The rate and scale of the high-energy bunches thus obtained agree with the observations. (3) The particle number density in the radiating region we found is much higher than that in the Goldreich-Julian model [1], and thus explaining the observed high density in the Crab pulsar pointed out in [2]. (4) Our model predicts that the γ-radiation and the radio radiation of a given neutron star may have different pulse periods.

A statistical determination of the location of emission in pulsars based on a new classification

Abstract 83 pulsars are statistically studied in this paper. The main results are as follows: 1. (1) Taking the ratio λ of the loss rate of rotational energy to the radio luminosity of pulsars as a parameter of classification, we divide the 83 pulsars into 3 categories. The plots of P dot -P, L radio -P and L radio -t show that different categories of pulsars have different evolutionary tracks and physical properties. The evolutionary tracks of our 3 categories are similar to those of the model proposed by Lyne et al. (1975) [1] which involves a secular decay of magnetic dipole moment, suggesting that the different categories have different time constants of decay, or different initial values of magnetic moment at birth. 2. (2) The radio luminosities of pulsars of various categories are all closely correlated with the magnetic energies and “twining” magnetic energies at the light cylinder, and not correlated with the magnetic energies at the surface of the neutron star. This shows that localized radiation regions are in the vicinity of the light cylinder. These magnetic energies may be the energy sources of pulsar radiation. 3. (3) The rightmost pulsars in the P dot -P plot form a cut-off line of radio radiation, with a slope of −4, so that it is a line of constant “twining” magnetic energy. This line is closer to the observational results than the cut-off line, proposed by Lyne et al. (1975) [1], with a gradient of −5. This results gives support to the idea that energy is accumulated and released in the vicinity of the light cylinder.

Estimation of some parameters of pulsars and their applications

The estimation of some important parameters of pulsars is discussed. The results have been compared with the RS model and applied to the estimation of radio luminosity and the beaming factor.

Distribution of apparent beamwidths of pulsars and evolution of their magnetic inclinations

Abstract We analyse the distribution of the apparent beamwidth in a sample of 195 pulsars with known ages. Assuming the polar cap model, we derive the expression for the conditional density of α at given magnetic inclination φ. We then derive the frequency distribution of φ in each of four age groups. We find the distribution shows a preference for small values, 73% of the total having φ ≤ 30°. There is also a tendency for φ to decrease with age.

Two-Component Model for the Interstellar Scattering along the Line of Sight to the Pulsar PSR B0136+57

A rigorous treatment of the refractive scintillation caused by a two-component interstellar scattering medium and a Kolmogorov form of density spectrum is discussed. It is assumed that the interstellar scattering medium is composed of a thin screen ISM and an extended interstellar medium. We conclude that the refractive scintillation caused by this two-component ISM scattering gives a more satisfactory explanation for the observed flux density variation than the single extended medium model along the line of sight to the pulsar PSR B0136+57.

Polarization observations of four southern pulsars at 1560 MHz

Abstract We present some interesting results from the mean pulse polarization observations of four southern pulsars made at the Australian National Radio Astronomy Observatory, Parkes, using the 64-m telescope in June and July, 1988. The 2 × 16 × 5 MHz filter system from Jodrell Bank has proved excellent in de-dispersing the pulse signals and measuring their polarization properties. We give the data for the four pulsars in some detail and discuss their spectral behaviour.