A Statistical Study of a Large Sample of Changing-look Active Galactic Nuclei with Multi-frequency Radio Sky Surveys

Abstract

Optically “changing-look” active galactic nuclei (AGNs) are a class of objects that exhibit appearance or disappearance of broad lines. Recent studies have shown that these “changing-look” activities very likely result from the accretion activities of the central supermassive black holes. Large variation of the accretion rate might cause jet ejection and fading events, thus lead to a certain variability of observational radio properties. From the published literature, 74 “changing-look” AGNs and 90 “changing-look” AGNs candidates identified in optical observations were collected. Based on this largest, complex, and incomplete sample to date, the radio properties of “changing-look” AGNs were investigated. The radio counterparts of 51 “changing-look” AGNs (including 21 candidates) were discovered from the all-sky surveys conducted by the Australian Square Kilometre Array Pathfinder (ASKAP) and Very Large Array (VLA) covering the frequency range of 0.9–3 GHz. This corresponds to a detection rate of about 41 percent, which is similar to general AGNs. The radio spectral indices between 0.9 and 1.4 GHz and between 1.4 and 3 GHz were calculated, which suggest that these “changing-look” AGNs tend to have flatter radio spectra than normal AGNs. This statistical result indicates that “changing-look” AGNs might host some young, compact, and faint radio jets.