Abstract
We present results of ASCA observations of the low-luminosity AGN (LLAGN) NGC 4579 in 1995 July and 1998 December which show evidence for spectral variability. The X-ray luminosity in the 1998 observations is 2×1041 ergs s−1 in the 2–10 keV band and about 35% larger than in 1995. An Fe K emission line is clearly detected in both observations. The center energy is 6.73−0.12+0.13 keV in 1995 and 6.39±0.09 keV in 1998. If we model the Fe line with two Gaussians centered at 6.4 keV and 6.7 keV, the line intensity of the 6.7 keV line decreased while that of the 6.4 keV line increased within an interval of 3.5 years. This variability rules out thermal plasmas in the host galaxy as the origin of the ionized Fe line in this LLAGN. The detection of a variable 6.4 keV line suggests that an optically thick standard accretion disk is present in this object, whose Eddington ratio is only LBol/LEdd∼2×10−3.
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