PCA of PCA: principal component analysis of partial covering absorption in NGC 1365
Abstract
We analyse 400 ks of XMM-Newton data on the active galactic nucleus NGC 1365 using principal component analysis (PCA) to identify model-independent spectral components. We find two significant components and demonstrate that they are qualitatively different from those found in MCG-6-30-15 using the same method. As the variability in NGC 1365 is known to be due to changes in the parameters of a partial covering neutral absorber, this shows that the same mechanism cannot be the driver of variability in MCG-6-30-15. By examining intervals where the spectrum shows relatively low absorption we separate the effects of intrinsic source variability, including signatures of relativistic reflection, from variations in the intervening absorption. We simulate the principal components produced by different physical variations, and show that PCA provides a clear distinction between absorption and reflection as the drivers of variability in AGN spectra. The simulations are shown to reproduce the PCA spectra of both NGC 1365 and MCG-6-30-15, and further demonstrate that the dominant cause of spectral variability in these two sources requires a qualitatively different mechanism.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- June 2014
- DOI:
- 10.1093/mnras/stu712
- arXiv:
- arXiv:1404.2611
- Bibcode:
- 2014MNRAS.441.1817P
- Keywords:
-
- galaxies: active;
- galaxies: individual: NGC 1365;
- galaxies: individual: MCG-6-30-15;
- galaxies: Seyfert;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 8 pages, 10 figures. Accepted for publication in MNRAS