Dynamical analysis of the complex radio structure in 3C 293: Clues on a rapid jet realignment in X-shaped radio galaxies

TL;DR

This study investigates the recent jet realignment in the X-shaped radio galaxy 3C 293, revealing a rapid change in jet orientation likely caused by black hole spin flips during a post-merger phase.

Contribution

It provides detailed spectral modeling of 3C 293's lobes, estimating their ages and energetics, and supports the Lense-Thirring precession model for jet realignment in post-merger galaxies.

Findings

Outer lobes are ~60 Myr old, inner lobes ~0.3 Myr old.

Jet power is consistent with Blandford-Znajek mechanism at low black hole spin.

Evidence supports rapid jet axis flip due to black hole spin interactions.

Abstract

Radio galaxies classified as X-shaped/winged, are characterised by two pairs of extended and misaligned lobes, which suggest a rapid realignment of the jet axis, for which a potential cause is still under debate. Here we analyse the complex radio structure of 3C 293 winged source hosted by the post-merger galaxy, which uniquely displays a significant asymmetry between the sizes of the two pairs of lobes, indicating that an episode of jet realignment took place only very recently. Based on all the available radio data for 3C 293, we have performed a detailed spectral modelling for the older and younger lobes in the system. In this way we derived the lobes' ages and jet energetics, which we then compared to the accretion power in the source. We found that the 200 kpc-scale outer lobes of 3C 293 are ~60 Myr old and that jet activity related to the formation of the outer lobes ceased within the last Myr. Meanwhile, the inner 4 kpc-scale lobes, tilted by ~40 deg with respect to the outer ones, are only about ~0.3 Myr old. The best model fits also return identical values of the jet power supplying the outer and the inner structures. This power is of the order of the maximum kinetic luminosity of a Blandford-Znajek jet for a given black hole mass and accretion rate, but only in the case of relatively low values of a black hole spin, a~0.2. The derived jet energetics and timescales, along with the presence of two optical nuclei in 3C 293, all provide a strong support to the Lense-Thirring precession model in which the supermassive black hole spin, and therefore the jet axis, flips rapidly owing to the interactions with the tilted accretion disk in a new tidal interaction episode of the merging process. We further speculate that, in general, X-shape radio morphology forms in post-merger systems that are rich in cold molecular gas, and only host slowly spinning supermassive black holes.