The naked nuclei of LINERs
  We analyze HST spectra and Chandra observations of a sample of 21 LINERs, at
least 18 of which genuine AGN. We find a correlation between the X-rays and
emission lines luminosities, extending over three orders of magnitude and with
a dispersion of 0.36 dex; no differences emerge between LINERs with and without
broad lines, or between radio-loud and radio-quiet sources. The presence of
such a strong correlation is remarkable considering that for half of the sample
the X-ray luminosity can not be corrected for local absorption. This connection
is readily understood since the X-ray light is associated with the same source
producing the ionizing photons at the origin of the line emission. This implies
that we have a direct view of the LINERs nuclei in the X-rays: the
circumnuclear, high column density structure (the torus) is absent in these
sources. Such a conclusion is also supported by mid-infrared data. We suggest
that this is due to the general paucity of gas and dust in their nuclear
regions that causes also their low rate of accretion and low bolometric
luminosity.
