  The group of 7 thermally emitting and radio-quiet isolated neutron stars
(INSs) discovered by ROSAT constitutes a nearby population which locally
appears to be as numerous as that of the classical radio pulsars. So far,
attempts to enlarge this particular group of INSs finding more remote objects
failed to confirm any candidate. We found in the 2XMMp catalogue a handful of
sources with no catalogued counterparts and with X-ray spectra similar to those
of the ROSAT discovered INSs, but seen at larger distances and thus undergoing
higher interstellar absorptions. In order to rule out alternative
identifications such as an AGN or a CV, we obtained deep ESO-VLT and SOAR
optical imaging for the X-ray brightest candidates. We report here on the
current status of our search and discuss the possible nature of our candidates.
We focus particularly on the X-ray brightest source of our sample, 2XMM
J104608.7-594306, observed serendipitously over more than four years by the
XMM-Newton Observatory. A lower limit on the X-ray to optical flux ratio of ~
300 together with a stable flux and soft X-ray spectrum make it the most
promising thermally emitting INS candidate. Beyond the finding of new members,
our study aims at constraining the space density of this population at large
distances and at determining whether their apparently high local density is an
anomaly or not.
