We evaluate the distance to pulsars and the location of the effective scattering layer of turbulent medium along the line of sight on the base of analysis diffractive and refractive scintillation of pulsars. In some cases our estimations of distances to pulsars as more than 3 times differ from the values quoted in the TML pulsar catalog.

Several studies in the last decade have explored dramatic instances of refractive fringing in dynamic spectra. We draw attention to a subtler but more widespread refractive effect: wisp-like structures extending (either linearly or with curvature) outward from the origin in the secondary spectrum plane. We have employed a simple pinhole screen simulation to investigate this phenomenon. It appears that the presence of one or more wisps in a secondary spectrum indicates a clump of scattering material that is significantly offset from the optical axis. Unlike the dramatic fringing events that have been investigated in the past, however, the interference that gives rise to a wisp is interference between rays within a scattering clump rather than between two major ray bundles. Furthermore, the scattering clump must be significantly elongated along the direction of pulsar motion. The range of fringe spacings that this produces, all with a similar slope in the secondary spectrum, gives rise to the linear extent of the wisp in the secondary spectrum.

Extreme Scattering Events are radio-wave lensing events caused by AU-sized concentrations of ionised gas. Although they were discovered more than a decade ago we still have no clear picture of the physical nature of the lenses. To discriminate between the various models, we need to amass more information on multiple imaging phenomena. Pulsars are perfect targets for such studies: they offer six- to ten-times the information content of quasar observations, and their small angular sizes make them sensitive to distant lenses. In addition, small source-size means that multiple imaging can be studied even when there is little change in the total source flux, because the (weak) secondary images interfere with the primary and create periodic fringes in the spectrum.

Radio signals, during their passage through the intervening medium, are scattered due to irregularities in the density of free electrons in the interstellar medium. Signals from distant sources undergo, most often, strong & multiple scattering while the signals from nearby sources may be only weakly scattered even at meter wavelengths. It is likely that the scattering of signals from some nearby sources is possibly non-multiple in nature and hence may show a distinct signature of single or discrete scattering events. In such a situation we receive, along with the direct unscattered signal, only a few discrete delayed versions of the signal. In such a case, it appears possible to probe the properties (such as the size and the density contrast) of the discrete density-irregularities responsible for the scattering, if the associated delays can be measured.

We show that variability of the radio source associated with the gamma ray burst of May 8, 1997 can be explained by scintillations on interstellar plasma inhomogeneities in the weak regime at 4.86 and 8.46 GHz, and by the refractive component of saturated scintillations at 1.43 GHz. Cosmological distance of this source R ≊ 1028 cm is more preferable. The source has the size about 2 μarcsec at frequency 4.86 GHz and the velocity of spreading is about 25 μarcsec/year.

Identified neutron star (NS) classes evidently are determined by several intertwined features: kinematics of NS at their formation (spin and translational); magnetic field strength; and binary membership. I discuss the well-known classes of isolated and accreting NS while keeping in mind recent discoveries of magnetars, anomalous X-ray pulsars, and long-period radio pulsars. I summarize the results of several likelihood analyses on radio pulsars, which yield information on the velocity distribution, luminosity function, and birth rate of high-field radio pulsars. I review the evidence for the occurrence of momentum kicks at the time of NS birth. Discerning the relationship of the classic radio pulsars to the more exotic classes probably requires careful comparison of magnetic fields, kinematics and birthrates, a program for the next millenium. Exciting discoveries of classic pulsars will also be made: sub-millisecond pulsars, massive binaries in fast orbits and truly hyper-velocity pulsars that shed light on core-collapse processes in supernovae.

The coalescence of close binary systems with two compact objects (neutron stars and black holes) are considered to be promising sources of gravitational waves for the currently built laser interferometers. Here, I review the current Galactic coalescence estimates derived both theoretically and empirically. I discuss the uncertainties involved as well as ways of obtaining an upper limit to the coalescence rate of two neutron stars.

We investigate the statistical evolution of magnetic neutron stars recycled in Low Mass Binary (LMB) systems, simulating synthetic populations. Irrespective to the details of the physical models, we find to be significant the fraction of neutron stars spinning close to their mass shedding limit relative to the millisecond pulsar population. The simulated neutron stars show a tail in their period distribution at periods shorter than 1.558 ms, the minimum detected so far. Crustal magnetic field decay models predict also the existence of massive rapidly spinning neutron stars with very low magnetic moment.

Twenty millisecond radio pulsars have now been observed in the globular cluster 47 Tuc. This is by far the largest sample of radio pulsars known in any globular cluster. These recent observations provide a unique opportunity to re-examine theoretically the formation and evolution of recycled pulsars in globular clusters.

We present an updated list of direct strong evidence in favour of kicks being imparted to newborn neutron stars. In particular we discuss the new cases of evidence resulting from recent observations of the X-ray binary Circinus X-1 and the newly discovered binary radio pulsar PSR J1141–6545. We conclude that the assumption that neutron stars receive a kick velocity at their formation is unavoidable (van den Heuvel & van Paradijs 1997).

This assumption explains a large variety of observations, ranging from direct observed properties of individual binary pulsars and Be/X-ray binaries to the observed birth rates and dynamical properties of the populations of LMXBs, binary recycled pulsars as well as the motion and distribution of single pulsars. Below we give an updated list in favour of kicks based on the compilation given by van den Heuvel & van Paradijs (1997) – see references therein for details.

Alternative ways are discussed in which pulsars may (1) drive their winds, (2) avoid net electric currents, (3) emit coherent radio pulses, (4) acquire high spin rates, and (5) deal with moderate surface magnetic fields: 1011 < B/G ≲ 1014.

We have derived a formula for the braking index of pulsars via integration rather than the conventional differentiation method. We applied the method to 20 pulsars and find that virtually all the derived braking indices are dominated by the effects of (unseen) glitches, the recovery from which corrupts the value of . However, any real, large, positive braking index has implications for magnetic field decay and offers support to recent models of pulsar evolution.

The Taylor expansion of the generalized spin-down equation = − f(v), derives into the multipolar equation = −gv5 – rv3 − sv), which is used here to study pulsar evolution. The coefficients g, r and s can be physically associated to gravitational radiation, magnetic dipolar radiation and particle aceleration. The multipolar expansion with constant coefficients cannot describe the P Ṗ diagram in a consistent manner and therefore it is unlikely a generalized equation of the form = −f(v;t) can be used to describe pulsar evolution. A more general form, = − f(v; t) can be investigated giving to the coefficients g, r and s time dependence. We consider some explicit functional forms for g(t), r(t) and s(t) which are consistent with observational and theoretical constraints.

The occurence of a quark matter core in rotating compact stars has been investigated within general relativity as a function of both the rotational frequency and the total baryon number. We demonstrate that the deviation of the braking index from n = 3 signals not only the occurence but also the size of a quark matter core in a pulsar. We suggest that in systems with mass accretion onto a rapidly rotating compact star a spin-down to spin-up transition might signal a deconfinement transition in its interior.

The rapid braking on the white dwarf in the close binary AE Aqr can be explained in terms of the canonical pulsar mechanism provided the magnetic moment of the star μ ∼ 1.5 × 1034 G cm3. The scenario for the origin of the fast rotating (Ps = 33 s), magnetized white dwarf, which is based on the magnetic field amplification in differentially rotating stars, is presented.

Within recent nonperturbative approaches to the effective quark interaction the diquark condensate forms a superconductor of second kind. Therefore the magnetic field will not be expelled from the superconducting quark core in accordance with observational data which indicate that life times of pulsar magnetic fields exceed 107 years.

The new plasma mechanism for the magnetic field generation in Crab Nebula is suggested. The mechanism is based on the development of two-stream instability after the supernova explosion.

Properties of the thermal radiation emitted by neutron stars (NSs) are determined by thin plasma layers (atmospheres) at their surfaces. The NS atmospheres are very different from those of usual stars due to the immense gravity and huge magnetic fields. Current models of hydrogen NS atmospheres show that the spectra deviate substantially from blackbody spectra of the same temperatures. Comparison of the model spectra with recent observations of soft X-ray and UV-optical radiation of NSs yields the surface temperatures considerably lower than those obtained from the blackbody fits. This conclusion have important implications for theories of NS cooling and for understanding fundamental properties of the superdense matter in the NS interiors.

We study equilibrium properties of partially ionized hydrogen atmospheres and subphotospheric layers of weakly (with magnetic field B ≪ 109G) and strongly (B ≫ 1010G) magnetized neutron stars. In both weak- and strong-field cases, the ionization degree, atomic occupation numbers, and equation of state are calculated. These results are used to calculate opacities of neutron-star atmospheres.

Thermal and electrical electron conductivities are calculated for a broad range of physical parameters typical for envelopes of neutron stars. An appropriate effective electron-ion scattering potential is used, based on calculations involving modified ion structure factors suggested recently for the treatment of the transport problems in dense Coulomb plasmas. These results are applied to calculation of the thermal structure of neutron-star envelopes.