ASCA Observations of the Seyfert 2 Galaxy NGC 7582: An Obscured and Scattered View of the Hidden Nucleus

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Published
1998-10-01
DOI
  • 10.1093/pasj/50.5.519
  • 10.48550/arxiv.astro-ph/9809086
Publisher
Oxford University Press (OUP)

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<jats:p>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× 1023 cm−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 ∼ 4×1022 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 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.</jats:p>

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