A radio counterpart of the local little red dot J092359+415736
Year: 2026
Type: article
Abstract: Context. Little red dots (LRDs) are compact red sources at z ≳ 4. Broad lines suggest accreting black holes, yet radio and X-ray measurements are usually weak. Local LRDs permit multi-frequency, multi-epoch radio studies inaccessible at high redshift. Aims. We aim to determine whether archival radio images contain a counterpart to the local LRD J092359+415736 at z ≈ 0.323, to quantify its long-term radio variability, and to identify the plausible physical origin of the radio emission. Methods. We measured the flux density at the optical position in FIRST, LoTSS, RACS, VAST, and VLASS products covering 0.144–3.0 GHz and 1994–2024, and assessed long-term variability across the three-decade baseline. Results. A compact 144 MHz counterpart is detected at 42 σ in LoTSS, coincident with the Gaia position, and is recovered in FIRST, RACS, VAST, and VLASS. The LoTSS and ASKAP measurements give α ≃ −0.30 ± 0.11. The source exhibits multi-timescale radio variability: FIRST at 1.4 GHz (1994) is a factor of ∼2.6 below the ASKAP measurements at similar frequencies (2021–2024) and below the extrapolated LoTSS–ASKAP spectrum, indicating long-term brightening over 26 yr, while the 3 GHz flux density rises by 2.3 σ between VLASS epochs 2.2 and 3.2, suggesting shorter-term variability. A star-formation-only origin would require a rate of ≃200 M ⊙ yr −1 , compared with an unobscured H α upper limit of 3.3 M ⊙ yr −1 , and hence an extreme, heavily obscured starburst. Ordinary single radio supernova and tidal disruption events are strongly disfavoured by the luminosity and 30-yr recovery history, while refractive interstellar scintillation, if responsible, itself requires an ultracompact nuclear emitter. Conclusions. The persistent radio counterpart of J092359+415736 is best explained by accretion onto its central black hole. Among the three radio-detected local LRDs, it is intermediate in luminosity and the only one with reported multi-year variability, adding a temporal dimension to the emerging radio diversity of the class.
Source: Astronomy and Astrophysics
Authors: Tao An, Ruqiu Lin, Ailing Wang
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
OpenAlex ID: W7221813571