The X-ray source CXO J133815.6 + 043255 has counterparts in the UV , optical , and radio bands .
Based on the multi-band investigations , it has been recently proposed by \citet kim15 as a rarely-seen off-nucleus ultraluminous X-ray ( ULX ) source with a black hole mass of \geq 10 ^ { 4 } ~ { } \mathrm { M } _ { \odot } in the nearby Seyfert galaxy NGC 5252 .
To explore its radio properties at very high angular resolution , we performed very long-baseline interferometry ( VLBI ) observations with the European VLBI Network ( EVN ) at 1.7 GHz .
We find that the radio counterpart is remarkably compact among the known ULXs .
It does not show a resolved structure with a resolution of a few milliarcsecond ( mas ) , and the total recovered flux density is comparable to that measured in earlier sub-arcsecond-resolution images .
The compact radio structure , the relatively flat spectrum , and the high radio luminosity are consistent with a weakly accreting supermassive black hole in a low-luminosity active galactic nucleus .
The nucleus of NGC 5252 itself has similar radio properties .
We argue that the system represents a relatively rare pair of active galactic nuclei , where both components emit in the radio .