Exploring The Effects Of Disk Thickness On The Black Hole Reflection Spectrum

TL;DR

This paper investigates how finite disk thickness influences the black hole reflection spectrum, revealing effects like spectral truncation and enhancement, which could impact measurements of black hole properties.

Contribution

It introduces a new relativistic ray tracing suite to model complex disk geometries and assesses the systematic errors caused by ignoring disk thickness in spectral analysis.

Findings

Finite disk thickness causes spectral truncation and enhancement.

Neglecting disk thickness can lead to systematic errors in black hole spin measurements.

The new model provides more accurate interpretations of reflection spectra.

Abstract

The relativistically-broadened reflection spectrum, observed in both AGN and X-ray binaries, has proven to be a powerful probe of the properties of black holes and the environments in which they reside. Being emitted from the inner-most regions of the accretion disk, this X-ray spectral component carries with it information not only about the plasma that resides in these extreme conditions, but also the black hole spin, a marker of the formation and accretion history of these objects. The models currently used to interpret the reflection spectrum are often simplistic, however, approximating the disk as an infinitely thin, optically thick plane of material orbiting in circular Keplerian orbits around the central object. Using a new relativistic ray tracing suite (Fenrir) that allows for more complex disk approximations, we examine the effects that disk thickness may have on the reflection spectrum. Assuming a lamp post corona, we find that finite disk thickness can have a variety of effects on the reflection spectrum, including a truncation of the blue wing (from self-shadowing of the accretion disk) and an enhancement of the red wing (from the irradiation of the central 'eye wall' of the inner disk). We make a first estimate on the systematic errors on black hole spin and height that may result from neglecting these effects.