A lower limit to the accretion disc radius in the low-luminosity AGN NGC 1052 derived from high-angular resolution data

TL;DR

This study uses high-angular resolution data to establish a lower limit on the truncation radius of the accretion disc in the low-luminosity AGN NGC 1052, revealing a truncated disc at least 26 gravitational radii from the black hole.

Contribution

First to derive a lower limit on the accretion disc truncation radius using only high-angular resolution observations.

Findings

Accretion power is insufficient for a standard disc at the innermost regions.

The disc must be truncated at r_tr ≥ 26 r_g to match observed luminosity.

The truncation radius aligns with X-ray Fe Kα line observations.

Abstract

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.