2020ApJ...890...40K

We report the detection of an intriguing parsec-scale radio source in the "offset AGN" candidate, KISSR 102. The elliptical host galaxy includes two optical nuclei at a projected separation of 1.54 kpc, N1 and N2, to the southeast and northwest, respectively. Phase-referenced Very Long Baseline Array observations at 1.5 and 4.9 GHz of this low ionization nuclear emission line region galaxy have detected double radio components (A and B) at a projected separation of 4.8 parsec at 1.5 GHz, and another partially resolved double radio structure at 4.9 GHz coincident with the brighter radio component A. These radio detections are confined to the optical nucleus N1. The brightness temperatures of all the detected radio components are high, >=10⁸ K, consistent with them being components of a radio active galactic nucleus (AGN). The 1.5-4.9 GHz spectral index is inverted (α ∼ + 0.64 ± 0.08) for component A and steep for component B (α <= -1.6). The dramatic change in the spectral indices of A and B is inconsistent with it being a typical "core-jet" structure from a single AGN, or the mini-lobes of a compact symmetric object. To be consistent with a "core-jet" structure, the jet in KISSR 102 would need to be undergoing strong jet-medium interaction with dense surrounding media resulting in a drastic spectral steepening of the jet. Alternatively, the results could be consistent with the presence of a parsec-scale binary radio AGN, which is the end result of a three-body interaction involving three supermassive black holes in the center of KISSR 102.