The twin-jet system in NGC 1052: VLBI-scrutiny of the obscuring torus

Abstract

Abstract. NGC 1052 offers the possibility to study the obscuring torus around a supermassive black hole, predicted by the standard model of active galactic nuclei, over a wide range of wavelengths from the radio to the X-ray regime. We present a detailed VLBI study of the parsec-scale structure of the "twin-jet" system in NGC 1052 in both total and polarized intensity and at multiple frequencies. We report the detection of linearly polarized emission from the base of the eastern jet at 5 GHz. While the radio spectrum in this region might be still consistent with synchrotron self absorption, the highly inverted spectrum of the western jet base represents a clear sign of pronounced free-free absorption in a circumnuclear torus. We observe an abrupt change of the brightness temperature gradient at a distance of ∼0.2 pc to 0.3 pc east of the central engine. This might provide an observational signature of the edge of the central torus, where the transition from an external pressure-dominated jet regime to a more or less freely expanding jet takes place. We determine the absorbing column density towards the western jet core to be ∼2.2 × 10 22 cm −2 in good agreement with the values derived from various X-ray observations. This suggests that the nuclear X-ray emission and the jet emission imaged by VLBI originate on the same scales.

Multiwavelength observations of the γ-ray flaring quasar S4 1030+61 in 2009–2014

“…Thus, our data well meet a powerlaw decrease of the brightness temperature with distance and component's size. The derived value of the power-law f at parsec scales agrees with theoretical predictions for a straight and a continuous conical jet (Kadler et al 2004;, although the brightness temperature of the jet beyond 5 mas downstream experiences a deviation from the power-law, where the jet bends.…”

“…Under an assumption of a stable conical jet with constant Lorentz factor of the emitting electrons and power-law dependences of the particle density, magnetic field strength, and jet transverse size, the brightness temperature for optically thin synchrotron emission should follow power law (see Kadler et al 2004) and 2.83 at 4.6 GHz. Thus, our data well meet a powerlaw decrease of the brightness temperature with distance and component's size.…”

Positional coincidence between an H2O maser and a plasma torus in NGC 1052

“…The spectrum index exceeds the theoretical limit for synchrotron self-absorption (α = 2.5). The highly inverted spectrum of the inner edge of the jets implies that synchrotron emission is obscured through free-free absorption (FFA) by the foreground dense plasma, and it is consistent with past multi-frequency observations (Kameno et al 2001, Vermeulen et al 2003and Kadler et al 2004.…”

“…The spectrum index exceeds the theoretical limit for synchrotron self-absorption (α = 2.5). The highly inverted spectrum of the inner edge of the jets implies that synchrotron emission is obscured through free-free absorption (FFA) by the foreground dense plasma, and it is consistent with past multi-frequency observations (Kameno et al 2001, Vermeulen et al 2003and Kadler et al 2004.Fitting the continuum spectrum at 15-43 GHz to FFA model (S ν ∝ ν −α exp (−τ ν −2.1 )), we obtained FFA opacity (τ ) distributions along the jet axis (figure 1), which reveals that a high opacity (τ > 1000) is found in the inner edge. It implies that the dense cold plasma covers ∼2 mas in the inner edge of the jets, where the central engine is supposed to exist.…”

Radio properties of CSSs and GPSs

“…Bicknell 2003) that also free-free absorption (FFA) may reproduce this anti-correlation. The low frequency turnover in the Kadler et al 2004). However in order to apply FFA in general, an accurate tuning of the ISM parameters is required.…”