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

Abstract

A key characteristic of many active galactic nuclei (AGN) is their variability, but its origin is poorly understood, especially in the radio domain. Williams et al. (2017) reported a ~50 per cent increase in peak flux density of the AGN in the Seyfert galaxy NGC 4151 at 1.5 GHz with the e-MERLIN array. We present new high resolution e-MERLIN observations at 5 GHz and compare these to archival MERLIN observations to investigate the reported variability. Our new observations allow us to probe the nuclear region at a factor three times higher-resolution than the previous e-MERLIN study. We separate the core component, C4, into three separate components: C4W, C4E and X. The AGN is thought to reside in component C4W, but this component has remained constant between epochs within uncertainties. However, we find that the Eastern-most component, C4E, has increased in peak flux density from 19.35$\pm$1.10 to 37.09$\pm$1.86 mJy/beam, representing a 8.2 sigma increase on the MERLIN observations. We attribute this peak flux density increase to continued interaction between the jet and the emission line region (ELR), observed for the first time in a low-luminosity AGN such as NGC 4151. We identify discrete resolved components at 5 GHz along the jet axis, which we interpret as areas of jet-ELR interaction.

arXiv comment9 pages, 3 figures, 1 table, accepted to MNRAS

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• Daily variability at milli-arcsecond scales in the radio quiet NLSy1 Mrk 110
• The nuclear architecture of NGC 4151: on the path toward a universal outflow mechanism in light of NGC 1068
• A compact core-jet structure in the changing-look Seyfert NGC 2617
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• Investigating Non-linear and Stochastic Hard X-ray Variability of Active Galactic Nuclei using Recurrence Analysis
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• The LeMMINGs survey: probing sub-kpc radio structures of nearby galaxies with e-MERLIN