2025/09/02 by Shun Hatano, Hatano, Shun, Masatoshi Imanishi +9
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #Gamma-ray bursts and supernovae #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · pdf · doi:10.48550/arxiv.2509.02254
openalex publication_date 2025/09/02 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We explore mid-infrared (MIR) variability in local ultraluminous infrared galaxies (ULIRGs; infrared luminsoity L\rm IR>1012 L_\odot) utilizing the ∼11 years of photometry from the NEOWISE multi-epoch catalog of \it Wide-field Infrared Survey Explorer (\it WISE). We identify 30 variable ULIRGs with statistically significant MIR variability. The variability is observed on timescales of a few years, implying that the MIR-emitting regions are compact (\lesssim 1 pc). The difference between maximum and minimum W2 (4.6 \rm μm) band luminosity (ΔL\rm W2) of the 30 variable ULIRGs range from ΔLW2 = 7×1042 to 5× 1044 erg s-1. The ΔLW2 of 25 variable ULIRGs out of 30 are greater than ΔLW2 = 1×1043 erg s-1, surpassing the MIR luminosity range observed in known supernovae (SNe; L_\rm 3.6 \rm μm and L_\rm 4.5 \rm μm < 1042.3 erg s-1). Therefore, the MIR variabilities in these 25 ULIRGs are most likely driven by tidal disruption events (TDEs) or intrinsic changes in their active galactic nuclei (AGN) torus emission. Our sample includes hard X-ray detected AGNs (e.g., UGC 05101) and previously reported TDE candidates (IRAS F01004-2237, IRAS 05189-2524). All 25 also exhibit at least one AGN signature(s) besides the MIR variability, suggesting that even if the MIR variability originates from TDEs, the black holes responsible are likely AGNs. Our results suggest that MIR variability is an effective tool for detecting buried AGNs and highlights the intense nuclear activity in ULIRGs.