Pulsar 0301+19, whose two well-separated components provide a textbook example of the conal double profile, apparently evolves to ajeingle form at frequencies above 5 GHz. PSR 2016+28, by contrast, exhibits a single form above 200 MHz, but bifurcates strongly and very asymmetrically below 100 MHz. In few pulsars can we see the full possibilities of conal profile evolution so clearly manifested.

We present average polarization profiles for 20 pulsars at 1720 MHz made with the 100-m Effelsberg radio telescope. All four Stokes parameters were appropriately delayed in a linear dedisperser to correct the interstellar dispersion on-line. Our sample includes a number of complex profiles which were observed polarimetrically for the first time at a high frequency, with the aim of describing their frequency evolution. Classification of the corrected profiles is attempted according to the empirical pulsar model described earlier by Rankin(1990).

We have developed a method to understand the detailed structure of the mean pulse profile of pulsars, namely, the Gaussian fit separation of the average profile (GFSAP) method, in which we assume the total profile is the superposition of several individual Gaussian-distributed components. Linear polarization data is used to simplify the fitting. The components of PSR 1451–68 are separated and their spectral indices calculated. We find that the profile of PSR 1451–68 is actually quintuple instead of triple, which is in agreement with the idea that quintuple is the prototype shape of pulsar profiles. The core component is shown to have the steepest spectrum, while the inner cone has the flattest. Another conclusion from PSR 1451–68 is that the core width does not change with frequency.

We present the results of mean pulse polarization observations at 1560 MHz of 8 pulsars with high southern latitude, large values of dispersion measure, short period and low flux density. All of these pulsars have strong linear polarization with a mean value of 47% and no previously published polarization data.

We discuss the cross-correlation analysis of single pulses in the emission of PSR 0329+54 observed simultaneously at 102.5 and 1700 MHz. We have found that the observed correlations between the two frequencies are consistent with the model in which the subpulses in single pulses correspond to plasma excitations flowing from the neutron-star surface along dipolar magnetic field lines. The peaks of strongly correlated subpulses at the two frequencies correspond to the same field line at two different emission radii. We have found that the core (central) and the conal (outer) components of the pulse profile of PSR 0329+54 originate at the same distance from the neutron star.

From December 1987 to February 1988 using the UTR-2 radiotelescope, we recorded the emissions of PSR 0823+26 and PSR 0943+10 at 25 and 16.7 MHz. Both pulsars are of considerable interest; PSR 0943+10 is one of several pulsars having two emission modes (Suleymanova and Izvekova 1984), and PSR 0823+26 has interpulse emission (Backer, Boriakoff, and Manchester 1973, Downs 1979) and dispersion measure, 19.466 pc cm–3. It is known that using the Arecibo telescope at 25 MHz one could succeed in recording only PSR 0919+06 with DM = 27.25 pc cm–3 (Phillips and Wolszczan 1989, 1990). In these papers, the presence of the two modes of PSR 0943+10 emission was confirmed.

Observations with double period integration (2Pobs) were used for the first time in 1972 to provide reliable detection of pulsars at low frequencies (Ustimenko 1983), where Pobs is the observed period. In 1973 observations of PSR 1919+21 were conducted with the period 4Pobs, during which interpulse emission (IPE) of that pulsar was found (Bruck and Ustimenko 1977b), later identified with observations at 38 MHz (Bash, Bozyan, and Torrance 1970, Bruck and Ustimenko 1977a). Later, because of the lower resolution, this method was not used, and its obvious advantages were forgotten. We returned to observations with 2Pobs integration period in 1987 to detect new pulsars, which proved necessary to overcome a number of difficulties and contradictions in identification of IPE.

Observations of PSR 1133+16 at frequencies of 20 and 25 MHz were conducted for the first time nearly 20 years ago (Bruck and Ustimenko 1973), and during the course of this work, its interpulse emission (IPE) was discovered. Systematic investigations of this pulsar at frequencies of 17, 20 and 25 MHz have been conducted using the UTR-2 radio telescope over the interval between 1972 and 1988, and occasional additional studies at 30 and 40 MHz were carried out since 1981 using DKR-1000 radio telescope. The form of the main pulse was studied and IPE searched for and investigated. The sporadic IPE components were identified on the basis of their intensity, their dispersion measure, and their time and frequency repeatability, and in some cases were confirmed by observations at different observatories.

Following the analysis by Krishnamohan and Downs (1983) of the Vela pulsar, we have investigated the behavior of the core and outrider components of PSR 0329+54 by calculating pulse profiles at different pulse intensities. VLA observations of individual pulses from PSR 0329+54 at 1415 MHz were used in our analysis. Our investigation reveals the following dependencies upon increasing core peak intensity:

1. (i) earlier core arrival times,

2. (ii) decreasing separation of the left outrider relative to the core,

3. (iii) increasing separation of the right outrider relative to the core,

4. (iv) decreasing outrider-to-core peak intensity ratios, and

5. (v) essentially constant core width.

To explain these dependencies, we propose a simple model in which the location of the core centroid is altered near the neutron star surface. The model and data are consistent with the mode-switching signatures and magnetospheric absorption features known to exist in this pulsar.

We report measurement of pulse profiles at 34.5 MHz of 8 pulsars using the Decameter-wave Radio Telescope at Gauribidanur, India. The dispersion measures of these pulsars range from 3 to 35 pc cm–3. None of the pulsars show any significant interpulse emission at this frequency which conflicts with earlier claims from 25-MHz observations (Bruck and Ustimenko 1976, Bruck and Ustimenko 1977a, Bruck and Ustimenko 1979). The intrinsic pulse width of PSR 1919+21 at 34.5 MHz appears to be smaller than at higher frequencies. These observations were made during the period 1984-86 and were reported by Deshpande (1987).

Some 15 members of the class of profiles with five components have been identified. These profiles have a central core component and two pairs of conal outriders, thus exhibiting the highest degree of formal complexity observed. No good examples of pulsars with six or more profile components are known.

Members of the five-component class have very similar physical parameters and emission-region geometries. An analysis of their emission geometry indicates both that the core and conal beams scale as P–1/2 and that the 1-GHz conal emission comes from a height of some 100-200 km.

Average pulse profiles at three frequencies are presented for PSR 1848+04. A highly structured pulse profile is seen (three-component main pulse, complex interpulse), with the longitudinal position of the pulse components invariant with frequency.

While millisecond pulsars have very different period parameters and a different evolutionary history compared to “normal” pulsars, the properties of their pulsed emission are remarkably similar to those of normal pulsars.

Super-hard γ-ray radiation spectra have been calculated. This radiation is generated near the velocity-of-light cylinder through the process of inverse-Compton scattering of relativistic electrons by thermal photons radiated by a neutron star. These calculations have been compared with observations of the Crab and Vela pulsars at 1000-GeV γ-ray energies. A correlation between γ-ray flares and those in soft (Ex ≃ lkeV) X-rays are predicted.

A magnetized neutron star may appear as a radio pulsar or an X-ray source. The latter is connected with a binary system where accretion from a normal star onto the neutron star produces X-ray emission. At the end of the evolution of a normal non-massive star, accretion stops and the neutron star becomes a recycled radio pulsar. Further evolution may lead to an additional transition from a radio pulsar to a low mass X-ray binary (LMXB). The formation of a single recycled pulsar is considered and a new mechanism of “enhanced evaporation” in globular clusters is analyzed.

The study of millisecond pulsars is of great astrophysical interest. One may expect that the rotation effect on the structure of the magnetosphere should be very significant. In view of the short duration of the pulses they are very suitable for investigations of the interstellar medium; at least they hold the promise for the pulsar time scale.

Millisecond pulsars were discovered and have been studied on the basis of their radio-emission at decimeter wavelengths. At longer wavelengths scattering of the radio emission in the interstellar medium is the principal limitation of millisecond pulsar observations.

According to general relativity, the spin axis of binary pulsar PSR 1913+16 should precess at a rate of 1.21 degrees per year. This precession will cause the pulse profile to change as our line of sight samples different pulsar latitudes. In order to search for this phenomenon, we have carefully monitored the pulse profile at 1408 MHz for 8.5 years. The ratio of flux density of the first to second pulse component has declined at a rate of approximately 1.65% per year, with some evidence of a steeper decrease over the past three years. We have detected no evidence for a change in the separation of the two components. We discuss the nature of the pulsar emission region in light of these results.

A simple approximate formula, expressing the maximum moment of inertia of a neutron star as a function of the mass and radius of the configuration with a maximum allowable mass, is shown to be a quite precise representation of the results obtained for a broad set of equations of state of dense matter. The resulting possible observational constraints in the mass-radius plane for neutron star models are discussed.

Even old (106 to 107 yr) pulsars within a few hundred parsecs of the Sun should give UV and optical fluxes via thermal radiation or radiation from relativistic particles. The surface temperature of a neutron star depends on its mass, radius, magnetic field, and internal composition (existence of pion condensate, superfluidity of nucléons, etc.). If the temperature exceeds ~2x104 K, the thermal radiation can be detected by the Hubble Space Telescope. An analysis of the results will allow one to study the thermal evolution and inner structure of neutron stars in order to obtain additional constraints on pulsar models.

An induced-collapse model [hereafter IC model; He et al. (1990)] can overcome the problems of the single star model of SN1987A. According to the IC model, there is a possibility that the SN1987A remnant will be a binary system with two neutron stars, one of them (SK-69 202) will have a strong magnetic field and a high surface temperature which favors detection as an X-ray or γ-ray pulsar. If the surface temperature of the neutron star cools down to T = 107 K, a radio binary pulsar is expected. There is also the possibility that an X-ray or γ-ray pulsar will be observed first, and only later will a radio pulsar will be detected.

A newly formed neutron star is thought to have a short (millisecond) period. In this case, the core emission beam is then very large (Qiao 1992) and is thus very likely to swing in the direction of the Earth.