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

We present the results of two ASCA observations of the Seyfert 2 galaxy NGC 7582. The observation in 1996 revealed the variablity at >99% confidence with the shortest timescale of ∼ 2 ×10 4 s. Variations were significant only in the hard X-ray band (2-10 keV) with the normalized variability amplitudeRMS ≈ 0.3, which is the same level as that of Seyfert 1 galaxies of the same luminosity. In the soft X-ray band (0.5-2 keV) the flux stayed almost constant. The source showed similar variability in another shorter observation in 1994. The overall broadband (0.5-10 keV) spectrum is complex. It shows a heavily absorbed (NH ∼ 1.0 × 10 23 cm −2 ) and flat ( ∼ 1.5) power-law continuum plus a slightly broad iron Kline at ∼ 6.4 keV with EW ∼ 170 eV. Below 2 keV, a "soft excess" emission dominates the spectrum. No significant variations in the average continuum and line fluxes were detected between the two ob- servations. However, the inferred column density increased by ∼ 4 × 10 22 cm −2 from 1994 to 1996. This variation could be interpreted in terms of "patchy torus", namely suggesting that absorbing material on our line-of-sight comprises many individual clouds. The observed iron line feature is also consistent with the picture of the transmission of nuclear X-ray continuum through the torus-like geometry. The nuclear X-ray luminosity (2-10 keV) is ∼ 3 × 10 42 ergs s −1 , similar to the typical values for Seyfert 1 galaxies. The constant 0.5-2 keV soft X-ray spectrum, though at least partially accounted for by some starburst contribution, could be interpreted mostly as the scattered central continuum from a spatially extended region. This is consistent with the lack of rapid soft X-ray variability. Thus NGC 7582 is a typical example of a type 2 Seyfert galaxy which exhibits both an obscured and scattered emission component as expected from the AGN unification model.