Investigation into the origin of the soft excess in Ark 564 using principal component analysis

¹ Department of Physics, Xiangtan University, Xiangtan, Hunan 411105, China
² Key Laboratory of Stars and Interstellar Medium, Xiangtan University, Xiangtan, Hunan 411105, China
³ Yunnan Observatories, Chinese Academy of Sciences (CAS), Kunming 650216, P.R. China
⁴ Key Laboratory for the Structure and Evolution of Celestial Objects, CAS, Kunming 650216, P.R. China

Received: 29 November 2023
Accepted: 7 June 2024

Abstract

We combined a principal component analysis (PCA) and spectroscopy to investigate the origin of the soft excess in narrow-line Seyfert 1 galaxy Ark 564 with XMM-Newton observations over a period of ten years. We find that the principal components in different epochs are very similar, suggesting stable variability patterns in this source. More importantly, although its spectra could be equally well fitted by the two soft excess models, simulations show that the principal components from the relativistically smeared reflection model match the data well. At the same time, the principal components from the warm corona model show significant inconsistency. This finding indicates that the soft excess in Ark 564 originates from the relativistically smeared reflection, rather than the Comptonization in the warm corona, thereby favoring the reflection origin or the “hybrid” origin of the soft excess. Furthermore, the presence of the narrow absorption features in the spectra suggests that the soft excess is unlikely to originate from absorptions due to possible outflowing winds. Our results indicate that the PCA coupled with spectral analysis is a promising approach to exploring the origin of the soft excess in active galactic nuclei (AGNs).