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Astron. Astrophys. 329, L45-L48 (1998)

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Letter to the Editor

Diffraction-limited 76 mas speckle masking observations
of the core of NGC 1068 with the SAO 6 m telescope *

M. Wittkowski 1, 2, Y. Balega 3, T. Beckert 2, W.J. Duschl 2, 1, K.-H. Hofmann 1 and G. Weigelt 1

1 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
2 Institut für Theoretische Astrophysik, Tiergartenstraße 15, D-69121 Heidelberg, Germany
3 Special Astrophysical Observatory, Nizhnij Arkhyz, Zelenchuk region, Karachai-Cherkesia, 357147, Russia

Received 23 January 1997 / Accepted 30 October 1997

Abstract

We present the first K-band bispectrum speckle interferometry of NGC 1068 with an angular resolution of [FORMULA] ([FORMULA] pc). 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 [FORMULA] mas [FORMULA] pc 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 [FORMULA] 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.

Key words: techniques: interferometric – galaxies: fundamental parameters – galaxies: nuclei – galaxies: photometry – galaxies: Seyfert – galaxies: individual: NGC 1068

* Based on data collected at the Special Astrophysical Observatory, Russia

Send offprint requests to: Markus Wittkowski, Bonn;
e-mail: mw@speckle.mpifr-bonn.mpg.de

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© European Southern Observatory (ESO) 1998

Online publication: December 16, 1997
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