Several aspects of observations of neutron stars and compact extragalactic radio sources are considered, with particular regard to their use in constraining certain astrophysical phenomena.
A theoretical treatment of the pulse arrival time analysis of millisecond pulsars is made; we consider how a detailed timing analysis can be used to quantitatively probe noise processes affecting the pulsar period and the propagation of the radiation. The intrinsic noise may be used to study the neutron star interior, while propagation effects due to gravitational perturbations of the neutron star and interstellar refraction of the emitted radio waves provide probes of the pulsar environment and the intervening plasma. In addition, important constraints on the background of cosmological gravitational radiation can be derived from timing such pulsars.
We consider the thermal X-rays emitted from a warm (105K ≲ Teff ≲ 3 x 106 K) neutron star, either cooling from its initial formation or heated by internal dissipation, accretion, etc. Constructing model atmospheres appropriate to such stars with various effective temperatures and elemental abundances, we calculate their emergent spectra and the bolometric correction for observation bands of various X-ray satellites. We conclude that the present limits on neutron star surface flux are even more constraining than those derived assuming that the spectra are blackbody and examine how this effects models of neutron star interiors, formation and cooling. We also examine the consequences of similar X-ray observations for neutron star models of various gamma-ray stars.
The refraction of radio waves from pulsars and other compact sources by interstellar plasma is also studied.We show how pulsar observations, in particular, can be used to characterise the large scale inhomogeneities in the ionized ISM and compute a number of observable effects for various electron density perturbation spectra. It is shown how similar refraction can account for the low and intermediate frequency variation of compact extragalactic radio sources. We argue that the observations indicate that more power is present in the large scale fluctuations than previously believed. In addition, single ~1014 cm scale clouds in a previously unrecognized dense, ionised phase of the ISM can apparently dominate the refractive scintillation for some lines of sight.
