Normalizing a relativistic model of X-ray reflection

Abstract

Aims. The only relativistic reflection model that implements a parameter relating the intensity incident on an accretion disk to the observed intensity is relxill. The parameter used in earlier versions of this model, referred to as the reflection strength, is unsatisfactory; it has been superseded by a parameter that provides insight into the accretion geometry, namely the reflection fraction. The reflection fraction is defined as the ratio of the coronal intensity illuminating the disk to the coronal intensity that reaches the observer. Methods. The relxill model combines a general relativistic ray-tracing code and a photoionization code to compute the component of radiation reflected from an accretion that is illuminated by an external source. The reflection fraction is a particularly important parameter for relativistic models with well-defined geometry, such as the lamp post model, which is a focus of this paper. Results. Relativistic spectra are compared for three inclinations and for four values of the key parameter of the lamp post model, namely the height above the black hole of the illuminating, on-axis point source. In all cases, the strongest reflection is produced for low source heights and high spin. A low-spin black hole is shown to be incapable of producing enhanced relativistic reflection. Results for the relxill model are compared to those obtained with other models and a Monte Carlo simulation. Conclusions. Fitting data by using the relxill model and the recently implemented reflection fraction, the geometry of a system can be constrained. The reflection fraction is independent of system parameters such as inclination and black hole spin. The reflectionfraction parameter was implemented with the name refl_frac in all flavours of the relxill model, and the non-relativistic reflection model xillver, in v0.4a (18 January 2016).

Spectral analysis of theXMM–Newtondata of GX 339–4 in the low/hard state: disc truncation and reflection

“…This appears straightforward to implement in xillver. Following our discussion, Dauser et al (2016) have implemented that definition in xillver v0.4a.…”

“…However, this definition disagrees with that in terms of the 20-40 keV flux ratio, and the disagreement can be very strong due to the beaming of both direct and reflection radiation toward the equatorial plane of a rotating BH. For that reason, the definition of Dauser et al (2014) has been implemented in relxill v0.4a (Dauser et al 2016).…”

AGN Coronae through a Jet Perspective

“…The time lags do not include the additional dilution factor that is later applied during the analysis. * denotes the fits which include an additional broad Fe Kα line via relline (Dauser 2015).…”

“…This very basic baseline model provides a good fit (χ 2 red < 1.5) to 25 of the 30 sources. For the five sources with reduced χ 2 larger than 1.5, we included excess absorption and/or a board Fe Kα line (relline, Dauser 2015). These components are denoted in Table 1.…”

On the Lamppost Model of Accreting Black Holes

“…This causes the flux reflected at a low-inclination angle, i, to be overestimated and the one at a high inclination, to be underestimated, which then affects assessments of h based on the fitted reflection strength (e.g., Parker et al 2014). The current version (v04.a) uses a reflection fraction parameter (Dauser et al 2016) taking into account relativistic transfer of reflected radiation from the disk. We find that the reflection amplitude of v0.4a roughly agrees with that of reflkerr for h  2.…”