In this paper we have shown that two different populations of halo neutron stars, accreting matter from molecular clouds present in the dark clusters (which compose the galactic dark matter) can be revealed in the X-ray band. The X-ray luminosity of the halo neutron stars (HNS) crossing dark clusters should be erg s-1, while that of the neutron stars bound in dark clusters (DCNS) is expected to be about erg s-1. We estimate the presence of object per square degree for each population of neutron stars. HNS may contribute substantially to the unresolved soft excess observed at high latitude in the XRB, while DCNS can be tentatively identified with some of the supersoft X-ray sources for which the identification with any known class of objects is missing. A correlation with the emission in other wavelengths (infrared and radio) due to absorption from the surrounding medium and/or pulsar activity can be expected in some cases.
As a final point we note that the detection of these X-ray halo sources can provide an independent test on the presence of baryonic dark clusters in the galactic halo. Moreover, we would like to mention that neutron stars in the galactic halo can be directely detected by microlensing experiments (Mollerach & Roulet 1996 ) and altough their expected optical depth is respect to the MACHOs optical depth, it is likely that experiments planned for the near future will detect these objects.
© European Southern Observatory (ESO) 1997
Online publication: June 30, 1998