Caught in the act: Measuring the changes in the corona that cause the extreme variability of 1H 0707-495

TL;DR

This study investigates how the X-ray emitting corona in galaxy 1H 0707-495 changes in size and structure during different luminosity states, revealing an expanding and contracting corona linked to luminosity variations.

Contribution

It provides the first detailed analysis of the corona's spatial extent changes using emissivity profiles and reverberation lags in a highly variable AGN.

Findings

Corona expands radially by 25-30% with increased luminosity.

Reverberation lags increase as luminosity rises, indicating vertical extent variation.

Spectrum softens with higher luminosity, consistent with an expanding corona.

Abstract

The X-ray spectra of the narrow line Seyfert 1 galaxy, 1H 0707-495, obtained with XMM-Newton, from time periods of varying X-ray luminosity are analysed in the context of understanding the changes to the X-ray emitting corona that lead to the extreme variability seen in the X-ray emission from active galactic nuclei (AGN). The emissivity profile of the accretion disc, illuminated by the X-ray emitting corona, along with previous measurements of reverberation time lags are used to infer the spatial extent of the X-ray source. By fitting a twice-broken power law emissivity profile to the relativistically-broadened iron K fluorescence line, it is inferred that the X-ray emitting corona expands radially, over the plane of the accretion disc, by 25 to 30 per cent as the luminosity increases, contracting again as the luminosity decreases, while increases in the measured reverberation lag as the luminosity increases would require also variation in the vertical extent of the source above the disc. The spectrum of the X-ray continuum is found to soften as the total X-ray luminosity increases and we explore the variation in reflected flux as a function of directly-observed continuum flux. These three observations combined with simple, first-principles models constructed from ray tracing simulations of extended coron self-consistently portray an expanding corona whose average energy density decreases, but with a greater number of scattering particles as the luminosity of this extreme object increases.