About relxill

general information about the model

relxill is a new reflection model, which can be readily used in common X-ray data analysis tools such as isis, xspec, or sherpa. It joins forces of the xillver reflection code (Garcia et al., 2010, 2011, 2013) and the relline ray tracing 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).

The current version has been completely re-written, leading to a more stable and faster model evaluation. Moreover, for some of the model flavors it is possible to use a multi-zone disk. This update solves the issue pointed out in some publications that the input spectrum changes throughout the disk due to GR energy shifts. Therefore results for the lamp post flavor relxill models will slightly differ to the previous version, while all other models produce identical results. The changes are mainly compensated by a decrease of the cutoff energy around 10%.

relxill on GitHub: you can also follow the development of the model on GitHub and download the model from there (https://github.com/thdauser/relxill/)

basic features of the relxill model package
  • simple line models and convolution models
  • the xillver reflection model
  • cutoff power law and nthcomp as primary continuum
  • relxill: combining xillver reflection with relativistic smearing
  • irradiation of the disk by broken power law or lamp post geometry
  • self-consistent normalization of primary and reflected spectrum
  • multi-zone disk for the primary spectrum in the lamp post geometry
  • predicting an ionization gradient assuming an alpha disk density profile
The Ionization Gradient in the relxill model

As of version 1.3.0, the relxill also includes a variant which allows for an ionization gradient. Either the shape of the gradient can be fitted as a power law, or the gradient is predicted from the alpha disk density profile.

The figure on the left shows the spectra for three different levels of ionization (left panel) with the associated ionization gradient (right panel). The dashed line shows the radius of maximal ionization.

Download and Installation

current version of the model: [v1.4.3]

First download all necessary files given in the download section. It is not necessary to download all reflection tables. If those are required, a warning is issued when executing the model.

To compile the model, put all of the downloaded files into a directory, and unpack them:

tar xfz relxill_tables.tgz
tar xfz relxill_model_v1.4.3.tgz

In order to compile the model, it is recommended that you call the provided compile-script by executing:

  chmod u+x ./compile_relxill.sh

In this way the path to the tables will be correctly set in the model code, allowing you to properly load the model from any location. If you have a Mac OSX and setting the table paths fails, you might need to edit the file and un-comment line marked for "Mac OSX".

ALTERNATIVE: If you don't want to use this compile script, you can also set the path to the tables by setting the environment variable "RELXILL_TABLE_PATH" to the directory which contains the tables.

Change Log

  • [1.4.3]: fixes small memory leak for the Cp-models using the standard tables - 2021-01-22
  • [1.4.2]: fixes memory problems if a 6-dim table was used - 2021-01-21
  • [1.4.1]: corrects the (loose) definition of the reflection fraction in the relxill (non-LP) type models, which now directly follows the xillver/pexrav definition of the flux. This implies that the normalization (i.e., the flux) now depends on the inclination as F=1/2*cos(incl). - 2021-01-06
  • [v1.4.0] improves the interpolation of the xillver reflection spectra. This mainly affects the logN parameter and the relative normalization of xillverD and relxillD type models. - 2020-10-07
  • [v1.3.10] Cp-type models can again be loaded using the standard xillver reflection table (xillver-comp.fits) - 2020-08-03
  • [v1.3.9] fixes model sometimes crashing for a few, specific values of spin - 2020-07-10
  • [v1.3.7] restricts Incl < 87 degrees in the lmodel.dat to be consistent with the provided tables - 2020-04-15
  • [v1.3.5] works with new heasoft and stricter compiler options - 2019-10-17
  • [v1.3.3] new model relxilllpionCp added, which provides the ionization gradient and a moving primary source, but now also for the nthcomp primary continuum. - 2019-08-09
  • [v1.3.2] add "beta" parmeter (velocity of the primary source) to the relxilllpion model - 2019-08-02
  • [v1.3.0] ionization gradient and high density models
    - Included model relxilllpion predicting an ionization gradient (more information is given in the model section)
    - Update of the high-density models (xillverD, relxillD) to include a larger range in Gamma up to 3.6 (table is now xillverD-5.fits) - 2019-07-12
  • [v1.2.0] reverting the wrong change for the emissivity profile introduced by 1.1.0, change (1). Information on the update from 1.0.x to 1.2.0 can be found in this pdf. Besides this change, the environment variable RELLINE_PHYSICAL_NORM has been added. If set to 1, it will return the acutal normalization of the relline and relconv type models (not recommended for fitting). - 2018-08-07
  • [v1.1.0] Major update and bug fix, mainly for the lamp post version. The spectral shape of the standard relxill remains unchanged. (1) The emissivity profile in the lamp post geometry has been corrected, leading to a steeper radial dependency. This change was incorrected and has been reverted in v1.2.0. (2) fixing a wrong normalization of the reflected spectrum, mainly affecting models with a large inclination angle (3) removing the re-normalization with RENORM_RELXILL_MODEL (4) updating the relativistic table, to achieve a more precise calculation of relativstic blurring for very low inclinations. - 2018-07-27
  • [v1.0.4] only applies to the LP model flavors
    fixed inconsistencies and problems with the normalization of the reflection component of relxilllp and relxilllpCp, affecting only LP sources at large height (>20Rg) and Rout<1000 Rg, or with Rin>R_ISCO. The spectral shape and therefore eventually fitting parameters were only affected if fixReflFrac=1,2 was set. Additionally, problems with caching which sometimes occured when changing the inclination by a large were also fixed. - 2018-03-07
  • [v1.0.3] fixed relconv normalization (same now as for the previous relxill version) and in relxilllpCp temperature is now correctly given in the rest frame of the primary source - 2017-12-06
  • [v1.0.2] solved segmentation fault if model was executed in folder without write permission - 2017-08-03
  • [v1.0.1] added possiblity to change the re-normalization behaviour of the models with the environment variable RENORM_RELXILL_MODEL - 2017-06-23
  • [v1.0.0] first version of the new relxill model, including now multiple zones for the LP-relxill model flavours. All other models produce the same results, but all models are evaluated significantly faster - 2017-06-08

relxill model flavors

relxill, relxillCp

Standard relativistic reflection model, modeling the irradiation of the accretion by a broken power law emissivity. Different flavors are for an incident spectrum by either the standard high-energy cutoff powerlaw or an nthcomp Comptonization continuum (Cp).

relativistic reflection in coronal geometry

relxilllp, relxilllpCp

The relativistic reflection model for the lamp post geometry, again for an incident cutoff powerlaw or nthcomp spectrum (Cp). The disk is split in multiple zones, which see a different incident spectrum due to relativistic energy shifts of the primary spectrum.

lamp post geometry

xillver, xillverCp

normal reflection models, given for different incident spectra; powerlaw with high-energy cutoff (xillver) or with a nthcomp Comptonization (xillverCp).

non-relativistic reflection model

relline, relline_lp

simple line model, available in the coronal and lamp post (lp) geometry

line model, corona, lamp post

relconv, relconv_lp

similar to the line models, but now as a convolution model being able to convolve any reflection

flexible convolution model

relxilllpion, relxilllpionCp

Model including an ionization gradient. Depending on the setting of the parameter ion_grad_type, the gradient can be either modeled empirically as power law, or is predicted assuming a simple alpha disk (Shakura & Sunyaev, 1973). Detailed information is given in the parameters section. Also includes a velocity of the primary source.

ionization gradient, lamp post

xillverD, relxillD, relxilllpD

Same as the standard reflection models (xillver, relxill, relxilllp) but allowing a higher density for the accretion disk (between 1015 to 1019 cm-3). However, the high-energy cutoff is fixed at 300 keV at the moment.

high density accretion disk models

relxill model parameters

In the following, a list of all model parameters ia given. Some parameters have a special meaning if their value is negative, as also indicated in the list below.


spin of the black hole in dimensionless units, negative values mean the accretion disk is counter-rotating with respect to the black hole

Rin, Rout

inner and outer radius of the accretion disk in gravitational radii. Can also be given in units of the ISCO, when it is set to negative values.


inclination towards the system with respect to the normal to the accretion disk

Index1, Index2, Rbr

the emissivity for the coronal flavor models is given as r-Index1 between Rin and Rbr and r-Index2 between Rbr and Rout. Rbr is measured in gravitational radii, but can also be given in units of the ISCO if given in negative values.


Height of the primary source above the black hole in gravitational radii. Can be given in units of the event horizon if set to negative values.


Velocity of the primary source, in units v/c. Allowed values range form 0 to 0.99.


reflection fraction, defined in the frame of the primary source as ratio of intensity emitted towards the disk compared to escaping to infinity (see Dauser+2016 for more details). If set to a negative value, only the reflected component is returned.


switch, which set to 0 allows to fit the reflection freely and if set to 1 fixed to the predicted value of the current parameter configuration in the lamp post geometry, returning the combined direct and returning radiation. If set to 2, the model behaves similar to 1, but is displaying information on the calculated reflection fraction, strength, fraction of photons falling into the black hole, and the grav. redshift from the observer to the primary source is given. Setting this parameter to 3 is the same as 1, but only returns the predicted reflected spectrum.


Ionization of the accretion disk, ranging from 0 (neutral) to 4.7 (heavily ionized). In case of an ionization gradient, it specifies either the ionization at the inner edge (power law type) or the maximal ionization at (11/9)²Rin (alpha type).


The iron abundance of the material in the accretion disk (in units of solar abundance).


Power law index of the incident spectrum.

Ecut, kTe

Parameter describing the observed high energy cutoff Ecut of the primary spectrum. In case of the nthcomp input spectrum it is given as electron temperature in the corona (kTe). Important: This means that for all LP-type models, Ecut is given in the frame of the observer and therefore the value at the primary source has to be calculated by multiplying with the redshift factor (see fixReflFrac=2). kTe is given at the primary source, as temperature of the plasma. In case of the standard coronal model, no energy shift is applied.


The density of the accretion disk (in cm-3) given in logarithmic units. Models not containing this parameter are calculated for a fixed density of 1015 cm-3.


redshift to the source


Specifies the ionization gradient. If set to 1, it will be modeled as power law. Setting it to 2 means it is calculated by assuming the density profile of an alpha disk, peaking at (11/9)²Rin (see logxi above). For convenience, setting it to 0 means constant ionization.


In case of a power law ionization gradient (ion_grad_type=1) this parameter specifies the index of the power law such that xi = r-xi_index with logxi giving the ionization at Rin .

Additional Information

  • NORMALIZATION of XILLVER/RELXILL The definition of the normalization is given in Dauser+2016 (Eq. A.1).
  • IONIZATION GRADIENT for the ALPHA DISK To calculate the gradient, we use a density profile of r3/2[1−(Rin/r)1/2 ]−2, which assumes a constant alpha parameter. As xillver is only calculated for a 45° incident angle, we correct the gradient for the incident angle according to xieff = xi * cos(45°) / cos(delinc) (see Dauser et al., 2013). By default the gradient is calculated on 100 zones in radial direction.
  • LOGXI For predicted values outside of the tabulated range, the reflection for neutral (logxi=0) or extremely ionized (logxi=4.7) is used. Therefore upper limit of logxi can be increased without leading to problems with the models. This might be especially helpful for the predicted ionization gradient.
  • NTHCOMP: The nthcomp model is the standard xspec local model. Hidden parameters for the calculation of the continum for every Cp-type model are that kT_bb=0.05 and inp_type=1.
  • RELLINE_PHYSICAL_NORM: Since [v1.2.0] the environment variable RELLINE_PHYSICAL_NORM can be set to 1, which will return the physical normalization of relline, relconv, and relxill type models. Setting this for fitting is not recommended. For all relxilllp-type models this normalization is used by default.