2003ApJ...599.1043N

We present new 6, 3.6, and 2 cm VLA radio observations of the nearby merger system NGC 3256, with resolutions of ∼100 pc, which reveal compact radio sources embedded in more diffuse emission at all three wavelengths. The two radio nuclei are partially resolved, but the two dominant compact sources that remain coincide with the two most powerful compact ultraluminous X-ray sources (ULXs) recently reported by Lira et al. The radio/X-ray ratios for these two sources are too high by factors of more than 100-1000 to be normal X-ray binaries. However, their radio and X-ray powers and ratios are consistent with low-luminosity active galactic nuclei (LLAGNs), and optical emission lines suggest the presence of a nuclear disk around the northern nucleus. If the two nuclear ULXs are LLAGNs, their associated black holes are separated by only ∼1 kpc, making them about 6 times closer to one another than those found recently in the merger galaxy NGC 6240. A third ULX on the outskirts of the merger is also a radio source and probably is a collection of supernova remnants. The remaining ULXs are not coincident with any source of compact radio emission and are consistent with expectations for beamed X-ray binaries or intermediate-mass black holes.