ASCA observations of the seyfert 2 galaxy NGC 7582: An obscured and scattered view of the hidden nucleus

Abstract

ASCA observations of the Seyfert 2 galaxy NGC 7582 revealed that it was highly variable on the timescale of ∼ 2 × 104 s in the hard X-ray band (2 - 10 keV), while the soft X-ray (0.5 - 2 keV) flux remained constant during the observations. The normalized variability amplitude in the hard X-ray band was σRMS ≈ 0.3, which is the same level as that of Seyfert 1 galaxies of the same luminosity ∼ 3 × 1042 erg s-1 (2-10 keV). The spectral analysis suggests that this object is seen through an obscuring torus with the thickness of NH ∼ 1.0 × 1023cm-2. The hard X-rays are an absorbed direct continuum from a hidden Seyfert 1 nucleus, while the soft X-rays are dominated by the scattered central continuum from an extended spatial region. We have an obscured/absorbed and a scattered view of this source as expected from the unification model for Seyfert galaxies. More interestingly, the inferred column density increased by ∼ 4 × 1022cm-2 from 1994 to 1996, suggesting a "patchy" torus structure, namely the torus might be composed of many individual clouds. The observed iron-line feature near 6.4 keV with the equivalent width of 170 eV is also consistent with the picture of the transmission of nuclear X-ray continuum through a non-uniform torus.