# The nature of the soft-excess and spectral variability in the Seyfert 1 galaxy Zw 229.015

## TL;DR

This study analyzes the spectral and temporal variability of the Seyfert 1 galaxy Zw 229.015 across multiple observations, finding that spectral changes are primarily driven by the power law continuum, with implications for the emission region's structure.

## Contribution

It provides a comprehensive multi-epoch analysis of Zw 229.015, favoring the soft Comptonisation model and suggesting the primary emission originates from a distant or thick accretion disc.

## Key findings

- Spectral states include bright-soft and dim-hard with continuum changes.
- Spectral variability is mainly due to the power law component, not absorber or reflector changes.
- Zw 229.015 shows similarities to other sources with strong soft-excess but weak reflection features.

## Abstract

We have carried out a systematic analysis of the nearby (z=0.0279) active galaxy Zw 229.015 using multi-epoch, multi-instrument and deep pointed observations with XMM-Newton, Suzaku, Swift and NuSTAR. Spectral and temporal variability are examined in detail on both the long (weeks-to-years) and short (hours) timescales. A deep Suzaku observation of the source shows two distinct spectral states; a bright-soft state and a dim-hard state in which changes in the power law component account for the differences. Partial covering, blurred reflection and soft Comptonisation models describe the X-ray spectra comparably well, but the smooth, rather featureless, spectrum may be favouring the soft Comptonisation scenario. Moreover, independent of the spectral model, the observed spectral variability is ascribed to the changes in the power law continuum only and do not require changes in the properties of the absorber or blurred reflector incorporated in the other scenarios. The multi-epoch observations between 2009 and 2018 can be described in similar fashion. This could be understood if the primary emission is originating at a large distance from a standard accretion disc or if the disc is optically thin and geometrically thick as recently proposed for Zw 229.015. Our investigation shows that Zw 229.015 behaves similar to sources like Akn 120 and Mrk 530, that exhibit a strong soft-excess, but weak Compton hump and Fe K${\alpha}$ emission.