X-shaped radio galaxy 3C 223.1: A ‘double boomerang’ with an anomalous spectral gradient

Abstract

A comparison of the recent LOFAR 144 MHz map of the radio source 3C 223.1 (J094124.028+394441.95) with the VLA maps at 4.9 GHz and 8.3 GHz that we built based on archival data, establishes this X-shaped radio galaxy (XRG) as a singularly robust case where the ‘wings’ exhibit a distinctly flatter radio spectrum than the primary lobes. The details of its anomalous spectral gradient are unravelled here with unprecedented precision. We also highlight the ‘double boomerang’ type radio morphology of this XRG. It appears plausible that the peculiar spectral gradient in this XRG is owed to particle acceleration associated with the rebounding of the collimated backflows of synchrotron plasma streaming through its two primary lobes, as they impinge upon and encounter the magnetic tension in the prominent dusty disk of the elliptical galaxy hosting this XRG. We also draw attention to an intriguing new morphological peculiarity among XRGs, namely, a lateral offset observed between the (parallel) axes of the two primary radio lobes.