AN EXTREME EXAMPLE OF A RADIO RELIC IN ABELL-4038

A radio source with a spectral index of -2.2 between 0.08 and 1.425 GH z has been observed at the Very Large Array (VLA) at 1.425 GHz with re solution similar to 3 arcsec. The projected linear length of the sourc e is 56 kpc with an average projected distance of 32 kpc from the cent roid of the rich southern cluster Abell 4038, assuming the source is i n the cluster. The physical parameters of the source include a high mi nimum-energy field (B-me) of 38 mu G, which is unusual for a source of low surface brightness and relaxed appearance, but is explained by it s unusually steep spectrum. Although its radio morphology has some cha racteristics of a narrow-angle-tail source (NAT), the absence of an id entified host galaxy (m(R) greater than or equal to 23.0) makes it unl ikely that the source is a working radio galaxy. The relic is probably the remains of an FR II radio galaxy that was once energized by a par ticular bright cluster elliptical now 18 kpc to its east. The density of the intracluster gas has been sufficient to confine the source and preserve its morphology, permitting the source to age and its spectrum to steepen through synchrotron and inverse Compton energy losses.