Exploring the complex X - ray spectrum of NGC 4051

Archival XMM-Newton data on the nearby Seyfert galaxy NGC 4051, taken in relatively high and low flux states, offer a unique opportunity to explore the complexity of its X-ray spectrum. We find the hard X-ray band to be significantly affected by reflection from cold matter, which can also explain a non-varying, narrow Fe K fluorescent line. We interpret major differences between the high and low flux hard X-ray spectra in terms of the varying ionisation (opacity) of a substantial column of outflowing gas. An emission line spectrum in the low flux state indicates an extended region of pho-toionised gas. A high velocity, highly ionised outflow seen in the high state spectrum can replenish the gas in the extended emission region over ∼10 3 years, while having sufficient kinetic energy to contribute significantly to the hard X-ray continuum.