SIMBAD references

We present results from a study of X-shaped sources based on observations using the Giant Metrewave Radio Telescope (GMRT). These observations were motivated by our low-frequency study of 3C 223.1, an X-shaped radio source, which showed that the wings (or low surface brightness jets) have flatter spectral indices than that of the active lobes (or high surface brightness jets), a result not easily explained by most models. We have now obtained GMRT data at 240 and 610 MHz for almost all the known X-shaped radio sources and have studied the distribution of the spectral indices across the sources. While the radio morphologies of all the sources at 240 and 610 MHz show the characteristic X-shape, the spectral characteristics of the X-shaped radio sources seem to fall into three categories, namely, sources in which (i) the wings have flatter spectral indices than the active lobes have, (ii) the wings and the active lobes have comparable spectral indices, and (iii) the wings have steeper spectral indices than the active lobes have. We discuss the implications of the new observational results on the various formation models that have been proposed for X-shaped sources.