Decoupling absorption and continuum variability in the Seyfert 2 NGC 4507

Abstract

We present the results of the Suzaku observation of the Seyfert 2 galaxy NGC 4507. This source is one of the X-ray brightest Compton-thin Seyfert 2s and a candidate for a variable absorber. Suzaku caught NGC 4507 in a highly absorbed state characterised by a high column density (NH \sim8 x10^23 cm^-2), a strong reflected component (R\sim 1.9) and a high equivalent width Fe K alpha emission line (EW\sim 500 eV). The Fe K alpha emission line is unresolved at the resolution of the Suzaku CCDs (sigma < 30 eV or FWHM < 3000 km s^-1) and most likely originates in a distant absorber. The Fe K beta emission line is also clearly detected and its intensity is marginally higher than the theoretical value for low ionisation Fe. A comparison with previous observations performed with XMM-Newton and BeppoSAX reveals that the X-ray spectral curvature changes on a timescale of a few months. We analysed all these historical observations, with standard models as well as with a most recent model for a toroidal reprocessor and found that the main driver of the observed 2-10 keV spectral variability is a change of the line-of-sight obscuration, varying from \sim4x10^23 cm^-2 to \sim9 x 10^23 cm^-2. The primary continuum is also variable, although its photon index does not appear to vary, while the Fe K alpha line and reflection component are consistent with being constant across the observations. This suggests the presence of a rather constant reprocessor and that the observed line of sight NH variability is either due to a certain degree of clumpiness of the putative torus or due to the presence of a second clumpy absorber.

14 pages, 7 figures, 5 tables. Accepted for publication in MNRAS

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