Constraining the Accretion Flow in the Supermassive Black Hole of NGC 4278

ABSTRACT Compact radio cores and/or weak jets are commonly detected in the majority of nearby low‐luminosity active galactic nuclei (LLAGNs), whose nuclear activity is generally attributed to a combination of hot accretion flows and outflows. NGC 4278 is a prominent supermassive black hole (SMBH) system that provides a valuable laboratory for investigating the interplay between accretion and jet production. By applying a coupled ADAF‐jet model, we achieve a good fit: the low‐frequency radio band is well described by synchrotron emission from nonthermal electrons in the jet, while the higher‐frequency radio component is predominantly due to inverse Compton scattering from ADAF electrons; the hard X‐ray band is likewise accounted for by ADAF. The SED fitting further yields key parameters of the central engine: the SMBH in NGC 4278 appears to be rapidly spinning, with a dimensionless spin , and only a minor fraction of the mass captured at the outer boundary actually reaches the black hole. These findings contribute to a deeper understanding of the accretion‐jet connection.