The radio properties and environment of the remarkable radio-quiet quasar E1821+643

E1821+643 is remarkable in two respects: (i) it is an intrinsically highly luminous ($$M_B \approx -27$$) quasar at relatively low redshift (z = 0.297); and (ii) it is known to lie in a rich cluster of galaxies but, unlike most other active galactic nuclei (AGN) in clusters, has no reported radio emission. We show that, although E1821+643 does indeed belong to the well-defined class of ‘radio-quiet’ quasars (RQQs), its extreme optical brightness does make it reasonably bright at radio wavelengths: radio maps of the quasar and a nearby cluster member, which together constitute a single 3.4-Jy 8C (38 MHz) source, show that the former has a compact core and a possible one-sided jet, while the latter is a normal cluster Fanaroff–Riley class I source. We use new CCD imaging to quantify the richness of the cluster of galaxies around the quasar, finding that with an Abell richness class >2 it is among the richest clusters known. Our conclusion is that E1821+643 is the clearest example to date of an RQQ whose environment is of the type normally thought to be associated exclusively with radio-loud AGN, namely a giant elliptical galaxy at the centre of a rich cluster.