부산대학교 도서관

We report the detection of radio emission coincident with the ultraluminous X-ray source (ULX) in Holmberg II. The radio emission is diffuse and resolved, covering an area ~60 by 40 pc in extent and well-matched to the recently discovered HeII nebula surrounding the X-ray source. Comparison of the radio and optical properties of this extended radio emission argue against its association with either an HII region or supernova remnant. This is additional evidence that this ULX is not powered by a stellar-mass object whose emission is relativistically beamed towards the observer, and thus is either a super-Eddington source or intermediate mass black hole as suggested by optical observations. Implications of this result to future and existing radio studies of ULXs are discussed.
Comment: 5 pages with 3 figures, to appear in ApJ Letters