| Abstract: We present the analysis of the fundamental plane of supermassive black hole accretion, an empirical correlation between black hole mass (MBH ), radio continuum luminosity (LR ), and 0.2–10.0 keV X-ray continuum luminosity (LX ), which reflects the coupling between accretion processes and jet production. Although this relation has been widely studied, its dependence on the physical properties of active galactic nuclei (AGNs), particularly in the low-luminosity regime, remains poorly understood, and the role of variability is still largely unexplored. In this work, we investigate the stability of the fundamental plane using a carefully filtered sample of quasi-simultaneous, multi-epoch X-ray and radio observations. X-ray data are drawn from XMM-Newton and Chandra, while radio
measurements are obtained from VLA and VLBA. These datasets are cross-matched with the SDSS DR16 catalog to derive black hole mass estimates. X-ray and radio observations are matched within a 50-day time window to minimize long-term evolutionary effects while preserving sensitivity to correlated variability. The final sample comprises approximately 60 sources with multi-epoch coverage. We construct the fundamental plane using these quasi-simultaneous measurements and examine whether the established empirical relation holds consistently for individual sources across different epochs. By tracking source movement within the LR –LX –MBH parameter space, we assess deviations from the canonical relation and explore the impact of variability on the disc–jet connection,
providing new observational constraints on accretion and jet physics in AGNs. |
