Fe-K Line Time variability and Ni abundance of Distant Reflector in Seyfert Galaxies

TL;DR

This study investigates the variability of Fe-K and Ni-K emission lines in Seyfert galaxies, revealing insights into the structure of the torus and elemental abundances through archival X-ray data analysis.

Contribution

It provides the first systematic analysis of Fe-K line variability timescales and Ni abundance in Seyfert galaxies using Suzaku and XMM-Newton data.

Findings

Fe-K line varies over 1000-2000 days, indicating torus origin.

Ni-K line detected in multiple galaxies with >2σ significance.

Ni to Fe abundance ratio estimated at approximately 1.9 times solar.

Abstract

We have performed systematic studies of narrow Fe-K line (6.4 keV) flux variability and Ni-K line intensity for Seyfert galaxies, using {\em Suzaku} and {\em XMM-Newton} archival data. Significant Fe-K line variability of several tens percents 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 torus, consistent with the view that X-ray reflection by torus is a main origin of a narrow Fe-K line. Ni-K line was detected with $>2\sigma$ level for the Circinus galaxy, Cen A, MRK 3, NGC 4388, and NGC 4151. A mean and variance of Ni-K$\alpha$ to Fe-K$\alpha$ line intensity ratio are 0.066 and 0.026, respectively. Comparing this with the Monte-Carlo simulation of reflection, Ni to Fe abundance ratio is 1.9$\pm$0.8 solar. We discuss the results and possibility of Ni abundance enhancement.