The birth of young radio jets in changing-look AGN: a population study

Sufia Birmingham, Charlotte Ward, Kristina Nyland, Dougal Dobie, Matthew J. Graham, David L. Kaplan, Tara Murphy

First listed 2025-07-02 | Last updated 2025-07-02

Abstract

Changing-Look Active Galactic Nuclei (CLAGN) are a rare subset of AGN that show significant changes to the flux of broad Balmer emission lines. Recent studies of CLAGN, such as 1ES 1927+654 and Mrk 590, have revealed that changes in the optically observed accretion rate are accompanied by changes in radio activity. We present a time-domain population study of 474 spectroscopically confirmed CLAGN at radio wavelengths using the Australia SKA Pathfinder Variable and Slow Transients Survey and the Very Large Array Sky Survey. We compare the radio properties of this CLAGN sample to a control sample of AGN that have not had recent changing-look events, and to AGN that were found to have transitioned from radio-quiet to radio-loud over 10-year timescales in VLASS. For 20 newly studied CLAGN detected in ASKAP VAST, we do not detect Mrk 590 or 1ES 1927+654-like fading of the radio flux in the 10 years following changing-look events. For 6 CLAGN with a sufficiently low redshift and high enough mass, we rule out a Mrk 590-like flare. We find that at the population level, CLAGN have higher VAST/VLASS detection rates, lower fractions of radio loudness, and higher variability rates in the 1 GHz frequency compared to the control AGN. Through VLA observations of radio SEDs and Magellan spectroscopic observations, we do not find evidence of a link between CLAGN and AGN that transitioned from radio-loud to radio-quiet in VLASS. We discuss the implications of this study for the physical mechanisms that drive enhanced accretion episodes.

Short digest

A population study of 474 spectroscopically confirmed changing-look AGN tracks their radio behavior with ASKAP VAST and VLASS to test whether optical state changes spawn newborn radio jets. Across 20 VAST-detected CLAGN, the authors see no Mrk 590– or 1ES 1927+654–like radio fading within ~10 years of the changing-look epoch, and for six low‑z, high‑mass objects they rule out a Mrk 590–like flare. Population-wide, CLAGN show higher VAST/VLASS detection and 1 GHz variability rates but lower radio‑loud fractions than a control AGN sample, and VLA SEDs plus Magellan spectra do not support a link to VLASS sources that transitioned from radio‑quiet to radio‑loud. The results imply enhanced accretion episodes often stir compact radio activity but rarely mirror the decadal jet turn‑on channel seen in RL-transition systems, constraining when and how young radio jets are born.

Key figures to inspect

• Figure 1: Compare CLAGN and control redshift and black-hole mass distributions to assess matching; this frames whether radio detection/variability differences are intrinsic rather than selection-driven.
• Figure 2: Inspect Mrk 590 and NGC 1566 radio light curves relative to the gray changing-look windows to gauge post‑event trends and the paper’s constraints on Mrk 590–like fading timescales.
• Figure 3: Examine VLASS radio contours over optical images for the nine CLAGN with extended structure to distinguish jet morphologies from circumnuclear stellar emission and read off physical scales.
• Figure 4: Read the distribution of radio luminosities for VLASS- vs VAST-detected CLAGN to see where the sample sits relative to common radio‑loudness cuts and how frequency/epoch selection impacts detections.