ASCA observations of the Seyfert 2 galaxy NGC 7582: Implications for the unified scheme of AGNs

Abstract

ASCA observations of the Seyfert 2 galaxy NGC 7582 revealed that it was highly variable on the timescale of ∼ 2×10 4 s in the hard X-ray band (2–10 keV), while the soft X-ray (0.5-2 keV) flux remained constant. The normalized variability amplitude in the hard X-ray band was σ RMS ≈ 0.3, which is the same level as that of Seyfert 1 galaxies of the same luminosity ∼ 3×10 42 erg s −1 (2–10 keV). The spectral analysis suggests that this object is seen through an obscuring torus with the thickness of N H ∼ 1.0 × 10 23 cm −2. The hard X-ray is an absorbed direct continuum from a hidden Seyfert 1 nucleus, while the soft X-ray is dominated by the scattered central continuum from a spatially extended region. We have an obscured/absorbed and a scattered view of this source as expected from the unification model for Seyfert galaxies. An interesting point is that the inferred column density increased by ∼ 4 × 10 22 cm −2 from 1994 to 1996, suggesting a “patchy” torus structure, namely the torus might be composed of many individual clouds. The observed iron line near 6.4 keV with EW of 170 eV is consistent with the torus picture.