Exploring the complex X-ray spectrum of NGC 4051

Abstract

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 ionization (opacity) of a substantial column of outflowing gas. An emission-line spectrum in the low-flux state indicates an extended region of photoionized gas. A high-velocity, highly ionized outflow seen in the high-flux state spectrum can replenish the gas in the extended emission region over ~10³ yr, while having sufficient kinetic energy to contribute significantly to the hard X-ray continuum.