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A key characteristic of many active galactic nuclei (AGN) is theirvariability, but its origin is poorly understood, especially in the radiodomain. Williams et al. (2017) reported a ~50 per cent increase in peak fluxdensity of the AGN in the Seyfert galaxy NGC 4151 at 1.5 GHz with the e-MERLINarray. We present new high resolution e-MERLIN observations at 5 GHz andcompare these to archival MERLIN observations to investigate the reportedvariability. Our new observations allow us to probe the nuclear region at afactor three times higher-resolution than the previous e-MERLIN study. Weseparate the core component, C4, into three separate components: C4W, C4E andX. The AGN is thought to reside in component C4W, but this component hasremained constant between epochs within uncertainties. However, we find thatthe Eastern-most component, C4E, has increased in peak flux density from19.35$\pm$1.10 to 37.09$\pm$1.86 mJy/beam, representing a 8.2 sigma increase onthe MERLIN observations. We attribute this peak flux density increase tocontinued interaction between the jet and the emission line region (ELR),observed for the first time in a low-luminosity AGN such as NGC 4151. Weidentify discrete resolved components at 5 GHz along the jet axis, which weinterpret as areas of jet-ELR interaction.

The curious activity in the nucleus of NGC 4151: jet interaction causing variability?