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By C Sait Memorie Della, S. Bhatnagar, A. P. Rao and Hatfield Uk

Abstract

Abstract. The nature of X-shaped sources is a matter of considerable debate: it has even been proposed that they provide evidence for black hole mergers/spin reorientation, and therefore constrain the rate of strong gravitational wave events (Merritt & Ekers 2002). Based on morphological and spectral characteristics of these sources, currently a strong contender to explain the nature of these sources is the ‘alternative ’ model of Lal & Rao (2007), in which these sources consist of two pairs of jets, which are associated with two unresolved AGNs. Detailed morphological and spectral results on milliarcsecond-scales (mas) provide a crucial test of this model, and hence these sources are excellent candidates to study on mas; i.e., to detect the presence/absence of double nuclei/AGNs, signs of helical/disrupted jets, thereby, to investigate spatially resolved/unresolved binary AGN systems and providing clues to understanding the physics of merging of AGNs on mas. We conducted a systematic study of a large sample of known X-shaped, comparison FR II radio galaxies, and newly discovered X-shaped candidate sources using Giant Metrewave Radio Telescope and Very Large Array at several radio frequencies. In our new observations of ‘comparison ’ FR II radio galaxies we find that almost all of our targets show standard spectral steepening as a function of distance from the hotspot. However, one source, 3C 321, has a low-surface-brightness extension that shows a flatter spectral index than the high-surfacebrightness hotspots/lobes, as found in ‘known ’ X-shaped sources

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