PKS B1400−33: An Unusual Radio Relic in a Poor Cluster

Abstract

We present new arcminute-resolution radio images of the low surface brightness radio source PKS B1400-33, which is located in the poor cluster Abell S753. The observations consist of 330 MHz Very Large Array, 843 MHz Molonglo Observatory Synthesis Telescope, and 1398 and 2378 MHz Australia Telescope Compact Array data. These new images, with higher surface brightness sensitivity than previous observations, reveal that the large-scale structure consists of extended filamentary emission bounded by edge-brightened rims. The source is offset to one side of symmetrically distributed X-ray emission that is centered on the dominant cluster galaxy NGC 5419. PKS B1400-33 is a rare example of a relic in a poor cluster with radio properties unlike those of most relics and halos observed in cluster environments. The diffuse source appears to have had an unusual origin, and we discuss possible mechanisms. We examine whether the source could be reenergized relic radio plasma or a buoyant synchrotron bubble that is a relic of activity in NGC 5419. The more exciting prospect is that the source is relic plasma preserved in the cluster gaseous environment following the chance injection of a radio lobe into the intracluster medium as a result of activity in a galaxy at the periphery of the cluster.