Most active galactic nuclei (AGNs) exhibit a narrow Fe Kα line at ~6.4 keV in the X-ray spectra, due to the fluorescent emission from cold material far from the inner accretion disk. Using XMM-Newton observations, Page et al. found that the equivalent width (EW) of the narrow Fe Kα line decreases with increasing luminosity (EW~L-0.17+/-0.08), suggesting a decrease in the covering factor of the material emitting the line (presumably the torus). By combining the archival Chandra HETG observations of 34 type 1 AGNs with XMM observations in the literature, we build a much larger sample with 101 AGNs. We find a similar X-ray Baldwin effect in the sample (EW~L-0.2015+/-0.0426) however, we note that the anticorrelation is dominated by the radio-loud AGNs in the sample, whose X-ray spectra might be contaminated by the relativistic jet. Excluding the radio-loud AGNs, we find a much weaker anticorrelation (EW~L-0.1019+/-0.0524). We present Monte Carlo simulations showing that such a weak anticorrelation can be attributed to the relative short timescale variations of the X-ray continuum.
The Astrophysical Journal
- Pub Date:
- June 2006
- Galaxies: Active;
- Galaxies: Quasars: Emission Lines;
- X-Rays: Galaxies;
- 21 pages, including 3 tables and 7 figures, ApJ 2006, v644 in press