Fe-K Line Time Variability and Ni Abundance of Distant Reflectors in Seyfert Galaxies

We have performed systematic studies of narrow Fe-K line (6.4 keV) flux variability and Ni-K line intensity for Seyfert galaxies, using Suzaku and XMM-Newton archival data. Significant Fe-K line variability of several tens of percent was detected for a pair of observations separated by 1000-2000 days (Cen A, IC 4329 A, NGC 3516, and NGC 4151) and 158 days (NGC 3516). These timescales are larger by a factor of 10-100 than the inner radius of the torus, consistent with the view that X-ray reflection by a torus is a main origin for a narrow Fe-K line. The Ni-K line was detected with a >2σ level for the Circinus galaxy, Cen A, MRK 3, NGC 4388, and NGC 4151. A mean and variance of the Ni-Kα to Fe-Kα line intensity ratios are 0.066 and 0.026, respectively. Comparing this with the Monte-Carlo simulation of reflection, the Ni to Fe abundance ratio is 1.9 ± 0.8 solar. We discuss the results and the possibility of Ni abundance enhancement.