Testing Accretion Disk Structure with Suzaku data of LMC X-3

TL;DR

This study uses Suzaku data of LMC X-3 to analyze the accretion disk spectrum, revealing the need for more complex models that include relativistic effects and additional physical processes to accurately describe disk emission.

Contribution

It provides the first detailed observational constraints on the accretion disk spectrum of LMC X-3, highlighting discrepancies with existing models and suggesting directions for more comprehensive physical modeling.

Findings

Disk spectrum broader than simple blackbody sum

Relativistic smearing strongly required

Models underestimate absorption edge deviations

Abstract

The Suzaku observation of LMC X-3 gives the best data to date on the shape of the accretion disk spectrum. This is due to the combination of very low absorbing column density along this line of sight which allows the shape of the disk emisison to be constrained at low energies by the CCD's, while the tail can be simultaneously determined up to 30 keV by the high energy detectors. These data clearly demonstrate that the observed disk spectrum is broader than a simple 'sum of blackbodies', and relativistic smearing of the emission is strongly required. However, the intrinsic emission should be more complex than a (color-corrected) sum of blackbodies as it should also contain photo-electric absorption edges from the partially ionised disk photosphere. These are broadened by the relativistic smearing, but the models predict ~ 3-5 per cent deviations for 1/3- 1 solar abundance around the edge energies, significantly stronger than observed. This indicate that the models need to include more physical processes such as self-irradiation, bound-bound (line) absorption, and/or emission from recombination continuua and/or lines. Alternatively, if none of these match the data, it may instead require that the accretion disk density and/or emissivity profile with height is different to that assumed. Thus these data demonstrate the feasibility of observational tests of our fundamental understanding of the vertical structure of accretion disks.