SIMBAD references

Analysis of Giant Metrewave Radio Telescope low-frequency data for an X-shaped source, 3C 223.1, has revealed an unusual result. The radio morphologies of it at 240 and 610 MHz show a well defined X shape with a pair of active jets along the north-south axis and a pair of wings along the east-west axis, which pass symmetrically through the undetected radio core. The wings (or low-surface-brightness jets) have flatter spectral indices with respect to the high-surface-brightness jets; this confirms the earlier marginal result obtained at high frequency by Dennett-Thorpe et al. (2002). Although unusual, it is a valuable result which puts stringent constraints on the formation models and the nature of these sources. This result clearly shows the value of mapping the sample of X-shaped sources at low frequencies.