The optical counterpart to the radio object is a peculiar giant elliptical galaxy.

Ground-based telescopes later identified a fading optical counterpart as well.

It is a high-mass X-ray binary, with the optical counterpart being a variable star.

No optical counterpart has yet been discovered.

Some of the seven have very weak optical counterparts.

During the 1950s a number of bright radio sources had been discovered that did not appear to have an optical counterpart.

He and Baade also found optical counterparts to various radio sources.

His team showed in 1997 that gamma-ray bursts came from extragalactic sources, and identified optical counterparts.

Prior to the discovery of 3C 273, several other radio sources had been associated with optical counterparts, the first being 3C 48.

Approximately 50 other X-ray point sources are associated with luminous optical counterparts.