Diffraction-limited 76 mas Speckle Masking Observations of the Core of NGC 1068 with the SAO 6m Telescope

TL;DR

This study uses high-resolution speckle interferometry at the K-band to resolve the core of NGC 1068, revealing a slightly resolved nuclear structure likely representing a torus or scattering halo, providing insights into its physical properties.

Contribution

First K-band bispectrum speckle interferometry of NGC 1068 achieving 76 mas resolution, resolving the nuclear core and analyzing its structure and flux contributions.

Findings

The nuclear core is slightly resolved with a ~30 mas diameter.

The core likely represents a nuclear torus or scattering halo.

The spectrum suggests a possible scattering component influencing observed flux.

Abstract

We present the first K-band bispectrum speckle interferometry of NGC 1068 with an angular resolution of 76 mas (~5.5pc). This angular resolution allows us to attribute the measured flux to only one of the nuclear sources seen at radio wavelengths. The observed decreasing visibility function suggests that the dominant central core is probably not an unresolved point source, but slightly resolved with a FWHM diameter of ~30 mas ~2pc for an assumed Gaussian intensity distribution. This 30 mas object is possibly the nuclear torus and/or a scattering halo. We discuss different contributions to the observed K band flux. Between 5 GHz and the K-band the spectrum of this component is close to a nu^(1/3) proportionality. In addition to the standard interpretation of a hot dust torus surrounding the nucleus of NGC 1068, one cannot exclude the possibility that a sizeable fraction of the nuclear flux reaches us via a scattering halo. This then would allow us to determine physical parameters of the nuclear source.