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Unveiling the nature of the highly obscured AGN in NGC5643 with XMM-Newton

M. Guainazzi·P. Rodriguez-Pascual·A. C. Fabian·K. Iwasawa·G. Matt
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Abstract

We present results from an XMM-Newton observation of the nearby Seyfert 2 galaxy NGC5643. The nucleus exhibits a very flat X-ray continuum above 2 keV, together with a prominent K-alpha fluorescent iron line. This indicates heavy obscuration. We measure an absorbing column density N_H in the range 6-10 x 10^{23} atoms/cm/cm, either directly covering the nuclear emission, or covering its Compton-reflection. In the latter case, we might be observing a rather unusual geometry for the absorber, whereby reflection from the inner far side of a torus is in turn obscured by its near side outer atmosphere. The nuclear emission might be then either covered by a Compton-thick absorber, or undergoing a transient state of low activity. A second source (christened "X-1" in this paper) at the outskirts of NGC5643 optical surface outshines the nucleus in X-rays. If belonging to NGC5643, it is the third brightest (L_X ~ 4 x 10^{40} erg/s) known Ultra Luminous X-ray source. Comparison with past large aperture spectra of NGC 5643 unveils dramatic X-ray spectral changes above 1 keV. We interpret them as due to variability of the active nucleus and of source X-1 intrinsic X-ray powers by a factor >10 and 5, respectively.

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M. Guainazzi, P. Rodriguez-Pascual, A. C. Fabian, K. Iwasawa, G. Matt. 2004-08-17. Unveiling the nature of the highly obscured AGN in NGC5643 with XMM-Newton. https://doi.org/10.1111/j.1365-2966.2004.08317.x

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