Determination of the X-ray reflection emissivity profile of 1H 0707-495

TL;DR

This paper introduces a method to directly determine the X-ray reflection emissivity profile of an accretion disc in an AGN from observed spectra, revealing a twice-broken power law shape consistent with theoretical models.

Contribution

It presents a novel spectral fitting technique to recover the disc's emissivity profile directly from observational data, validated on synthetic spectra and applied to real XMM-Newton data.

Findings

Emissivity profile follows a twice-broken power law.

Inner disc region has a steep emissivity index of 7.8.

Outer regions tend toward a constant index of 3.3.

Abstract

When considering the X-ray spectrum resulting from the reflection off the surface of accretion discs of AGN, it is necessary to account for the variation in reflected flux over the disc, i.e. the emissivity profile. This will depend on factors including the location and geometry of the X-ray source and the disc characteristics. We directly obtain the emissivity profile of the disc from the observed spectrum by considering the reflection component as the sum of contributions from successive radii in the disc and fitting to find the relative weightings of these components in a relativistically-broadened emission line. This method has successfully recovered known emissivity profiles from synthetic spectra and is applied to XMM-Newton spectra of the Narrow Line Seyfert 1 galaxy 1H 0707-495. The data imply a twice-broken power law form of the emissivity law with a steep profile in the inner regions of the disc (index 7.8) and then a flat region between 5.6rg and 34.8rg before tending to a constant index of 3.3 over the outer regions of the disc. The form of the observed emissivity profile is consistent with theoretical predictions, thus reinforcing the reflection interpretation.