Abstract
We use the full broad-band XMM-Newton European Photon Imaging Camera (EPIC) data to examine the X-ray spectrum of the nearby Seyfert 2 galaxy NGC 1068, previously shown to be complex with the X-ray continuum being a sum of components reflected/scattered from cold (neutral) and warm (ionized) matter, together with associated emission-line spectra. We quantify the neutral and ionized reflectors in terms of the luminosity of the hidden nucleus. Both are relatively weak, a result we interpret on the unified Seyfert model by a near side-on view to the putative torus, reducing the visibility of the illuminated inner surface of the torus (the cold reflector), and part of the ionized outflow. A high inclination in NGC 1068 also provides a natural explanation for the large (Compton-thick) absorbing column in the line-of-sight to the nucleus. The emission line fluxes are consistent with the strength of the neutral and ionized continuum components, supporting the robustness of the spectral model.
Highlights
At X-ray energies the low redshift Seyfert 2 galaxies NGC 1068 and Mrk 3 exhibit very ‘hard’ broad-band spectra due to strong absorption of the intrinsic X-ray continuum by a large column density of intervening cold matter
The cold-reflection-dominated continuum of Mrk 3 is evident in the extremely hard spectrum ( ∼ −0.5) below ∼6 keV, and in the deep absorption Fe K absorption edge at 7.1 keV. (We see later that the strong cold reflection in Mrk 3 results in it being as bright as NGC 1068 near ∼6 keV, despite being 3.5 times more distant.) Above ∼10 keV the much softer observed Mrk 3 spectrum is a consequence of the underlying ∼ 1.8 power law becoming visible through the marginally Compton-thick absorber
The hard X-ray ( 3 keV) spectra of both NGC 1068 and Mrk 3 have continuum components arising from reflection from cold matter, perhaps the putative molecular torus
Summary
At X-ray energies the low redshift Seyfert 2 galaxies NGC 1068 and Mrk 3 exhibit very ‘hard’ broad-band spectra due to strong absorption of the intrinsic X-ray continuum by a large column density of intervening cold matter (the torus?). Previous analyses of XMM–Newton European Photon Imaging Camera (EPIC) spectra (NGC 1068: Matt et al 2004, hereafter M04; Mrk 3: Pounds & Page 2005, hereafter P05) have confirmed earlier suggestions that the observed X-flux over the 3–10 keV band in these two nearby active galactic nucleus (AGN) is dominated by indirect radiation ‘reflected’ into the line-of-sight. High-resolution grating spectra from both XMM–Newton and Chandra have confirmed the soft X-ray band in both NGC 1068 and Mrk 3 to be dominated by line emission from a photoionized/photoexcited gas (NGC 1068: Kinkhabwala et al 2002; Ogle et al 2003; Mrk 3: Sako et al 2000; P05), with observed outflow velocities of 400–500 km s−1. The structure and dynamics of the putative torus can be probed in terms of
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