Ambilateral collimation study of the twin-jets in NGC1052

Abstract

Context: With the increased sensitivity and resolution of radio interferometry the study of the collimation and acceleration region of extragalactic jets in Active Galactic Nuclei (AGN) has come into focus within the last years. Whereas a large fraction of AGN jets reveal a change from parabolic to conical collimation profile around the Bondi radius, there is a small number of sources which deviates from this standard picture, including the radio galaxy NGC 1052. Aims: We study the jet width profile, which provides valuable information about the interplay between the central engine and accretion disk system and the formation, acceleration, and collimation of the jets. Methods: We observed the double-sided, low radio power active galaxy NGC 1052 at six frequencies with the VLBA in 2017 and at 22 GHz with RadioAstron in 2016. These data are combined with archival 15, 22, and 43 GHz multi-epoch VLBA observations. From ridge-line fitting we obtained width measurements along the jet and counter-jet which were fitted with single and broken power-laws. Results: We find a clear break point in the jet collimation profile at ∼ 10 4 R S (Schwarzschild radii). Downstream of the break the collimation is conical with a power-law index of 1.0 -1.2 (cylindrical 0; parabolic 0.5; conical 1) for both jets. On the other hand the upstream power-law index of 0.36 for the approaching jet is neither cylindrical nor parabolic and for the receding jet with 0.16 close-to cylindrical. For both jets we find a large opening angle of ∼ 30 • at a distance of ∼ 10 3 R S and well collimated structures with an opening angle of < 10 • downstream of the break. Conclusions: There are significant differences in the upstream collimation profile between approaching (Eastern) and receding (Western) jet. Absorption or scattering in the surrounding torus as well as an accretion wind may mimic a cylindrical profile. We need to increase the observing frequencies, which do not suffer from absorption to find the true jet collimation profile upstream of 10 4 R S .