Multi-epoch X-ray spectral analysis of the narrow-line Seyfert 1 galaxy Mrk 478

TL;DR

This study analyzes 16 years of X-ray data from Mrk 478, comparing physical models to understand spectral variability, and finds blurred reflection models best explain the observed changes, indicating a rapidly spinning black hole with specific iron features.

Contribution

It provides a comprehensive multi-epoch spectral analysis of Mrk 478, comparing different physical models and favoring blurred reflection to explain spectral variability over time.

Findings

Blurred reflection models best explain spectral variability.

Black hole in Mrk 478 is likely rapidly spinning.

Detected narrow Fe xxv emission at 6.7 keV.

Abstract

A multi-epoch X-ray spectral and variability analysis is conducted for the narrow-line Seyfert 1 (NLS1) active galactic nucleus (AGN) Mrk 478. All available X-ray data from XMM-Newton and Suzaku satellites, spanning from 2001 to 2017, are modelled with a variety of physical models including partial covering, soft-Comptonisation, and blurred reflection, to explain the observed spectral shape and variability over the 16 years. All models are a similar statistical fit to the data sets, though the analysis of the variability between data sets favours the blurred reflection model. In particular, the variability can be attributed to changes in flux of the primary coronal emission. Different reflection models fit the data equally well, but differ in interpretation. The use of reflionx predicts a low disc ionisation and power law dominated spectrum, while relxill predicts a highly ionised and blurred reflection dominated spectrum. A power law dominated spectrum might be more consistent with the normal X-ray-to-UV spectral shape (aox). Both blurred reflection models suggest a rapidly spinning black hole seen at a low inclination angle, and both require a sub-solar (~0.5) abundance of iron. All physical models require a narrow emission feature at 6.7 keV likely attributable to Fe xxv emission, while no evidence for a narrow 6.4 keV line from neutral iron is detected.