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 characterized by a high column density (NH ~ 8 × 1023 cm-2), a strong reflected component (R ~ 1.9) and a high equivalent width FeKα emission line (EW ~ 500 eV). The FeKα emission line is unresolved at the resolution of the Suzaku CCDs [σ < 30 eV or full width at half-maximum (FWHM) < 3000 km s-1] and most likely originates in a distant absorber. The Fe Kβ emission line is also clearly detected and its intensity is marginally higher than the theoretical value for low ionization Fe. A comparison with previous observations performed with XMM-Newton and BeppoSAX reveals that the X-ray spectral curvature changes on a time-scale 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 ~4 × 1023 to ~9 × 1023 cm-2. The primary continuum is also variable, although its photon index does not appear to vary, while the FeKα 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. © 2012 The Authors.