Deep searches for isolated radio-quiet neutron stars
J. Truemper
¹ Max-Planck-Institut fuer extraterrestrische Physik, 85741 Garching, Germany

With ROSAT seven isolated neutron stars ("The Magnificent Seven") have been discovered characterised by blackbody spectra at temperatures of 400-800 x 10³ K and the absence of radio and high energy emissions. Observations with HST, Keck and VLT show faint optical counterparts (m ~ 24-29) with Rayleigh-Jeans type spectra ( ~ n² T) and large proper motions. These objects are interpreted as cooling neutron stars. They show weak modulations of the X-ray flux with periods of a few seconds. Proton cyclotron lines discovered with Chandra and XMM-Newton point to surface magnetic fields of ~ 10¹³ G, in rough agreement with estimates derived from \.P measurements. They are of great interest from the point of view of neutron star demography and physics. In particular they allow the determination of the photospheric radii of neutron stars and thus to constraints on the equation of state at supra-nuclear densities.

It would be highly desirable to increase the number statistics of these objects. There are many hidden candidates in the ROSAT, Chandra and XMM-Newton data banks, but their identification as cooling neutron stars requires the measurement of their optical spectra at faint magnitudes (m ~ 28-32).

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On 20 Oct 2005, 15:32.