Exploring the Effects of Disk Thickness on the Black Hole Reflection Spectrum

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 deduce the systematic errors on black hole spin and height that may result from neglecting these effects.

relxill_nk: A Relativistic Reflection Model for Testing Einstein’s Gravity

“…The issues of the uncertainties of the astrophysical model and of their impact on the measurements of the model parameters are extremely important and not explored yet. Even in the case of spin measurements under the assumption of the Kerr metric, there are only a few preliminary studies to estimate the systematic errors and to construct more sophisticated models [67,68].…”

Observing black holes spin

“…In particular, the degeneracy of spin signatures with those of accretion disk winds has sparked lively debate [20,21,22]. Recent work has also explored systematic errors in spin measurements that result from the finite thickness of the accretion disk [23], finding them to become increasingly relevant as one considers black holes with higher accretion rates.…”

Joint XMM-Newton and NuSTAR observations of the reflection spectrum of III Zw 2

“…This result is the same whether using our initial assumption on the maximum disk inclination (41 • ) or allowing the disk inclination to vary freely (see Table A.1). While the limit of a 0.98 corresponds to statistical uncertainties only and does not include systematic effects such as the finite thickness of the accretion disk (Taylor & Reynolds 2018), our results do favour a fast-spinning BH in a source that belongs to a group of radiointermediate quasars, which have been suggested to be relativistically beamed counterparts of radio-quiet quasars (Falcke et al 1996b). If the jet in III Zw 2 is indeed intrinsically weak, this suggests that spin is not the (only) parameter driving the vast differences in jet production efficiencies of accreting black holes.…”