Abstract. The origin of the local population of young, cooling neutron stars is investigated with a population synthesis model taking into account the contribution of neutron stars born in the Gould Belt, in addition to those originating in the Galactic disk. We estimate their emission in the soft X-ray band as a function of distance and age and construct the Log N-Log S distribution. It is shown that the inclusion of neutron stars from the Gould Belt provides a good fit to the observed Log NLog S distribution. As the Sun is situated inside the Gould Belt, one can naturally explain the comparative local overabundance of massive progenitors and can remove the difficulty of the deficit of relatively bright ( > ∼ 0.1 ROSAT PSPC cts s −1 ) cooling neutron stars previously reported from models where only neutron stars from the Galactic disk were accounted for.Key words. stars: neutron -stars: evolution -stars: statistics -X-rays: stars
IntroductionObservations of isolated neutron stars (INSs) are important for gaining deeper insight on their structure and thermal evolution and ultimately might prove decisive in unveiling the physical properties of matter at ultra-high densities. Up to a decade ago, the only known INSs were active radio pulsars, with the addition of the γ-ray pulsar Geminga. Despite the fact that X-ray emission from some radio pulsars was already detected by Einstein, it was in the 90's that ROSAT, thanks to its sensitivity in the 0.1−2 keV band, gave a clearer picture of the faint X-ray emission produced by the cooling surface of the closest INSs. ROSAT, supplemented by more recent observations by Chandra and XMM-Newton, revealed a variety of types of behavior in the X-ray emission from INSs and its relation with radio activity.In particular, a substantial contribution of ROSAT to this field has been the discovery of a group of seven radio- Since the seven RINSs have remarkably similar observed properties, it is quite natural to assume that they belong to the same class, i.e. all of them are close-by, cooling NSs. This, however, poses a major problem. A useful and standard way to study a population of sources is to compute the Log N-Log S distribution starting from a model, and then compare it with observations. This has been done for RINSs by Neuhäuser & Trümper (1999) and Popov et al. (2000b). The main conclusion of the latter investigation is that the typical spatial density of radio pulsars in our Galaxy is too low to explain RINSs. In other words, the assumption that RINSs and ordinary radio pulsars derive from the same parent population underpredicts the number of observed "coolers", i.e. NSs which are hot and close enough for their thermal emission to be detected in X-rays.An obvious solution is to invoke a local (both in space and time) overabundance of NSs with respect to those originating in the Galactic disk and seen now as radio pulsars. The main goal of this paper is to investigate the possible origin of these objects. Here we suggest that the likely birthplace for many of the INSs in th...