Abstract:We try to constrain the nuclear Equation-of-State (EoS)
by observations of neutron stars in our galactic neighbourhood.
There are seven thermally emitting neutron stars known from X-ray
and optical observations, the so-called Magnificent Seven (M7),
which are young (up to few Myr), nearby (one to few hundred pc),
and radio-quiet with blackbody-like X-ray spectra, so that
we can observe their surfaces.
As bright X-ray sources, we can determine their rotational (pulse) periods and their period derivatives from X-ray timing. From XMM and/or Chandra X-ray spectra, we can determine their temperatures. With precise astrometric observations using the Hubble Space Telescope, we can determine their parallax (i.e. distance) and optical flux. From flux, distance, and temperature, one can derive the radius.
This was recently re-done by us for RXJ1856 and RXJ0720. Then, from identifying atomic or cyclotron absorption lines in X-ray spectra and also from rotational phase-resolved spectroscopy, we can determine the compactness (mass/radius) and/or gravitational redshift. This has also just been successfully applied for one case (RBS1223). If also applied to RXJ1856 or RXJ0720, radius (from luminosity and temperature) and compactness (from X-ray data) will yield the mass and radius - for the first time for an isolated single neutron star without previous mass exchange. We will present our observations, methods, and recent results.