Complex UV/X-ray variability of 1H~0707-495

TL;DR

This study investigates the complex relationship between UV and X-ray variability in galaxy 1H~0707-495, revealing anti-correlations and insights into the origin of the soft X-ray excess and the nature of the X-ray corona.

Contribution

It provides new evidence against reprocessing and inward accretion fluctuations as primary UV variability mechanisms, and suggests a dynamic X-ray corona and reprocessed soft excess.

Findings

UV and X-ray variations anti-correlate on short and long timescales.

Soft X-ray excess is likely reprocessed emission from the inner accretion disc.

Indications of a non-static, variable X-ray corona.

Abstract

We study the relationship between the UV and X-ray variability of the narrow-line Seyfert 1 galaxy 1H~0707-495. Using a year long {\it Swift} monitoring and four long {\it XMM-Newton} observations, we perform cross-correlation analyses of the UV and X-ray light curves, on both long and short time scales. We also perform time-resolved X-ray spectroscopy on 1-2 ks scale, and study the relationship between the UV emission and the X-ray spectral components - soft X-ray excess and a power-law. We find that the UV and X-ray variations anti-correlate on short, and possibly on long time scales as well. Our results rule out reprocessing as the dominant mechanism for the UV variability, as well as the inward propagating fluctuations in the accretion rate. Absence of a positive correlation between the photon index and the UV flux suggests that the observed UV emission is unlikely to be the seed photons for the thermal Comptonisation. We find a strong correlation between the continuum flux and the soft-excess temperature which implies that the soft excess is most likely the reprocessed X-ray emission in the inner accretion disc. Strong X-ray heating of the innermost regions in the disc, due to gravitational light bending, appears to be an important effect in 1H~0707-495, giving rise to a significant fraction of the soft excess as reprocessed thermal emission. We also find indications for a non-static, dynamic X-ray corona, where either the size or height (or both) vary with time.