Investigation of emission from the surfaces of isolated neutron stars (NS) with the aid of advanced theoretical models of thermal radiation provides a unique opportunity to infer the NS surface temperatures, magnetic fields, chemical composition and, ultimately, NS masses and radii.
This information, supplemented with the model equations of state and NS cooling models, can lead to understanding the fundamental properties of the superdense matter in the NS interiors.
As the surface temperatures of isolated NSs observable at high energies are within a range from about a half to a few million degrees, soft X-rays (0.1-2 keV, approximately) are the key energy band for detecting and studying the NS thermal radiation.
Millisecond pulsars represent an evolutionarily distinct group among rotation-powered pulsars.
Outside the radio band, the soft X-ray range (0.1-10 keV) is most suitable for studying radiative mechanisms operating in these fascinating objects.
X-ray observations revealed diverse properties of emission from millisecond pulsars.
For most of them, the bulk of the radiation is of a thermal origin, emitted from small spots (polar caps) on the neutron star surface heated by relativistic particles produced in pulsar acceleration zones.
On the other hand, a few other very fast rotating pulsars exhibit almost pure nonthermal emission generated, most probably, in pulsar magnetospheres.
There are also examples of nonthermal emission detected from X-ray nebulae powered by millisecond pulsars, as well as from pulsar winds shocked in binary systems with millisecond pulsars as companions.
The X-ray astronomy group at MSFC has enjoyed an active and varied program of research
into the nature of galactic neutron stars and pulsars.
Among relevant publications are
these reviews on
theoretical and observational aspects of thermal emission from isolated Neutron Stars and
studying millisecond pulsars in X-rays.
Other papers of interest are these on the
First X-Ray Observations of the Young Pulsar J1357-6429,
XMM-Newton Observations of Four Millisecond Pulsars, the
Pulsar Wind Nebula of the Geminga Pulsar,
X-Ray Emission from the Old Pulsar B0950+08, and
Ultraviolet, X-Ray, and Optical Radiation from the Geminga Pulsar.