The Diversity of Neutron Stars
Nearby Thermally Emitting Neutron Stars and the Compact Central Objects in Supernova Remnants
by David L. Kaplan
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(free download) Synopsis
Neutron stars are invaluable tools for exploring stellar death, the
physics of ultra-dense matter, and the effects of extremely strong
magnetic fields. The observed population of neutron stars is
dominated by the >1000 radio pulsars, but there are distinct
sub-populations that, while fewer in number, can have significant
impact on our understanding of the issues mentioned above. These
populations are the nearby, isolated neutron stars discovered by
ROSAT, and the central compact objects in supernova remnants. The
studies of both of these populations have been greatly accelerated in
recent years through observations with the Chandra X-ray
Observatory and the XMM-Newton telescope. First, we discuss
radio, optical, and X-ray observations of the nearby neutron stars
aimed at determining their relation to the Galactic neutron star
population and at unraveling their complex physical processes by
determining the basic astronomical parameters that define the
population---distances, ages, and magnetic fields---the
uncertainties in which limit any attempt to derive basic physical
parameters for these objects. We conclude that these sources are
1e6 year-old cooling neutron stars with magnetic fields above
1e13 Gauss. Second, we describe the hollow supernova remnant
problem: why many of the supernova remnants in the Galaxy have no
indication of central neutron stars. We have undertaken an X-ray census
of neutron stars in a volume-limited sample of Galactic supernova
remnants, and from it conclude that either many supernovae do not
produce neutron stars contrary to expectation, or that neutron stars
can have a wide range in cooling behavior that makes many sources
disappear from the X-ray sky.