The BL Lac heart of Centaurus A

Abstract

A B S T R A C TWe have observed emission from the nucleus of the closest radio galaxy, Centaurus A, from the radio to the gamma-ray band. We construct, for the first time, its overall spectral energy distribution (SED) which appears to be intriguingly similar to those of blazars, showing two broad peaks located in the far-infrared band and at ,0.1 MeV respectively. The whole nuclear emission of Centaurus A is successfully reproduced with a synchrotron self-Compton model. The estimated physical parameters of the emitting source are similar to those of BL Lacs, except for a much smaller beaming factor, as qualitatively expected when a relativistic jet is orientated at a large angle to the line of sight. These results represent strong evidence that Centaurus A is indeed a misoriented BL Lac, and provide strong support in favour of the unification scheme for low-luminosity radio-loud active galactic nuclei. Modelling of the SED of Centaurus A also provides further and independent indications of the presence of velocity structures in sub-parsec-scale jets.

The Parsec-Scale Central Components of FR I Radio Galaxies

“…These correlations support the argument of Chiaberge, Capetti, & Celotti (1999), that the CCC radiation is of a non-thermal synchrotron origin, which is relativistically beamed along with the radio emission. We used the CCC data of 27 3CR FR Is in Chiaberge et al 1999;NGC 7052 and NGC 6251 in Capetti & Celotti (1999) and Hardcastle & Worrall (2000), respectively; 26 3CR FR lIs in Chiaberge, Capetti & Celotti (2000) and BL Lacs in . The Rj values come from the VLBI observations of Giovannini et al 1999 and references therein.…”

On the magnetization of BL Lac jets

“…We recall here that the existence of the postulated structure in BL Lac jets (and FRI radiogalaxies) is supported by a variety of observational and phenomenological arguments (e.g. Chiaberge et al 2000, Giroletti et al 2004, Piner & Edwards 2014, Nagai et al 2014) and also by numerical simulations (e.g. Rossi et al 2008).…”

Is cold gas fuelling the radio galaxy NGC 315?

“…The study of obscuration toward the central regions of these galaxies (see e.g. Chiaberge et al 1999;Chiaberge et al 2002;Worrall et al 2003;Balmaverde et al 2006) has shown that the nuclear disks in these galaxies are geometrically and optically thin. This suggests that the standard pc-scale geometrically thick torus is not present in these low-luminosity radio galaxies.…”