A lower limit to the accretion disc radius in the low-luminosity AGN NGC
  1052 derived from high-angular resolution data
  We investigate the central sub-arcsec region of the low-luminosity active
galactic nucleus NGC 1052, using a high-angular resolution dataset that covers
10 orders of magnitude in frequency. This allows us to infer the continuum
emission within the innermost $\sim {17}\,$pc around the black hole to be of
non-thermal, synchrotron origin and to set a limit to the maximum contribution
of a standard accretion disc. Assuming the canonical 10 per cent mass-light
conversion efficiency for the standard accretion disc, its inferred accretion
power would be too low by one order of magnitude to account for the observed
continuum luminosity. We thus introduce a truncated accretion disc and derive a
truncation radius to mass-light conversion efficiency relation, which we use to
reconcile the inferred accretion power with the continuum luminosity. As a
result we find that a truncated disc providing the necessary accretion power
must be truncated at $r_\text{tr} \gtrsim {26}\, r_\text{g}$, consistent with
the inner radius derived from the observations of the Fe K$\alpha$ line in the
X-ray spectrum of this nucleus. This is the first time to derive a limit on the
truncation radius of the accretion disc from high-angular resolution data only.
