The RELXILL Model v0.5a
2017-02-17

RELXILL is a new reflection model, joining forces of the XILLVER reflection code (link; Garcia et al., 2010, 2011, 2013) and the RELLINE code (Dauser et al., 2010, 2013). The striking new feature is that for each point on the disk the proper xillver-reflection spectrum is chosen for each relativistically calculated emission angle. The implications of this improvement and more details regarding the model are provided in Garcia & Dauser et al. (2014, ApJ, 782, 76) and Dauser & Garcia et al. (2014, MNRAS, 444, L100). See also this pdf for a short information on all models and their parameters. A full list of changes of previous versions can be found here.

v0.5a Major updated now adding the possibility to use a "nthcomp" continuum for the (relativistic) reflection. The new models are named with a "Cp" (see below for a detailed description) and require a new xillver table to be downloaded. Additionally the possibility to re-normalize the relxill models (any type) was added, which eases the burden on the fit algorithm, as normally a change in height, e.g., also changes the normalization. It can be activated by setting the environment variable "RELXILL_RENORM=1".

angle_image.png

Figure of an accretion disk, showing the predicted emission angle from GR ray tracing (upper panel: inclination 40°; lower panel: 80°; Garcia & Dauser, 2014, accepted by ApJ). It is evident that the emission angle at the inner parts, where most of the radiation is expected, does differ largely from the inclination angle. Therefore a proper relativstic treatment is necessary to take the angular effects into account.

General Information

By installing the new RELXILL model, all previous implementations of the relline-like and relconv-like models are automatically installed, too. These models are completely identical to the ones from the RELLINE installation (hence, no additional installation of relline is necessary to get the previous functionalities).

Usage and Parameters

The RELXILL model now includes by default the irradiating power law source. It's strength can be set by the parameter refl_frac. This reflection fraction is defined as the ratio of photons that hit the disk to those that reach infinity. Due to strong light bending effects, this value can easily be larger than 1. More details can be found in Dauser+2014. Note, that for a negative value of refl_frac, only the reflection component will be returned (similar to the pexrav model definition). The detailed definition of the reflection fraction can be found here: Dauser+2016, A&A, 590, A76. All information about the parameters of all relxill flavor models can also be found in this pdf: download

norm: defined as the normalization of xillver, including relativistic effects
refl_frac: reflection fraction: see RN for details (differences in the exact definition between relxill and relxilllp, as it depends on the geometry)
Ecut: cutoff energy in keV (the same for the power law and the reflection spectrum)
1: take angles properly into account
fixReflFrac: 0: free reflection fraction (determined by the refl_frac parameter)
1: fix reflection fraction to the lamp post value (i.e., the parameter refl_frac has NO meaning in this case)
2: free, (same as 1:), but now the reflection fraction is displayed on the screen

The meaning of the parameters is the same as for the separate models (see relline description). Moreover, as the angular effects are properly treated, no "guess" regarding a limb brightening or darkening law is needed anymore.

Download

To install, please download the following files. The "table_nthcomp.tgz" is optional, but necessary if you want to use the reflection models with a nthcomp input continuum.

last changes in version
relxill_code.tgz 2017-02-17 v0.5a
tables.fits.tgz (warning: 938MB) 2016-12-21 v0.4e
table_nthcomp.tgz (warning: 906MB) 2017-02-17 v0.5a

The installation is similar to the relline model (look here). Note that you can use the environment variable RELLINE_TABLES to point to the complete set of provided tables, including the xillver table.

The environment variable RELXILL_NUM_BINS can be used to set the internal number of bins on which RELXILL is calculated. This will speed up the calculation by a large amount but might produce incorrect results if set to low (see model description below for more information on how to use it).

The relxill models in the lamp post geometry are using the physically predicted normalization assuming a constant primary source flux. Due to gravitational redshift effects this might change for the observer and therefore the normalization of the model strongly depends on the height if the primary source. However, this behavior might create problems for fit algorithm. A re-normalization can therefore be forced by setting the environment variable "RELLINE_RENORM=1".

A Comparison between RELXILL and the angle averaged approach

relxill_spectrum

Relativistically smeared spectra using RELXILL (standard parameters: logxi=2, gamma=2, index=3, spin=0.99). Middle: Ratio between relxill and the conventional relconv*xillver. Right: Relative distribution of flux for different emission angles. Note the angle averaged approach, which is commonly used, assumes a flat distribution here.

The code here is still in BETA-test! Please contact me if you find bugs or encounter problems with the model.