XWIND

Analytic model for calculating line-profiles from outflowing winds in AGN. Specifically, this is designed for slow(ish) winds at BLR scales. It is originally designed with the Fe-K $\alpha$ complex in mind, but also allows for the convolution of the same transfer functions for any line species (under the strong assumption that their emissivity traces density in the same way as netral Fe-K $\alpha$). This code is specifically designed for use in XSPEC. For a non-XSPEC version, see PyXWIND.

If this model is used in your work, please cite: Hagen et al. (2026, submitted to A&A) (https://ui.adsabs.harvard.edu/abs/2026arXiv260122392H/abstract)

Note 1: Depending on your version of XSPEC you will need to use one of two available branches:

For XSPEC version $\geq$ v.15.1, use main branch
For XSPEC version < v.15.1, use old_xspec branch

This comes from recent changes in how XSPEC handles and compiles fortran code

Note 2: Within XWIND there are three submodels: xwindline, xwindconv, and xindfe. After installation these are called within XSPEC directly (i.e model xwindline). See below for a parameter description of each.

Requirements

A working HEASOFT installation. Must be compiled from Source code (otherwise local models do not work). If HEASOFT installs properly, then you will also fulfull the requierements for fortran compilors

Installation

Clone the repository
Option 1 (manual installation):
2.1 Open XSPEC, and cd into the /src directory
2.2 Within XSPEC type: initpackage xwind lmod_xwind.dat . This will compile the code, and assumes you are currectly within the directory containing the source code files.
2.3 Still within XSPEC type: lmod xwind .
Option 2 (quick automatic installation)
3.1 Open XSPEC in the top level directory
3.2 Run the compile script. Type: @compile.xcm (this does steps 2.2 and 2.3 for you)
(OPTIONAL EXTRA): By default you will have to run the lmod xwind . step each time you start a new XSPEC session. To avoid this, locate your xspec.rc file (typically located in the .xspec/ directory within the home directory). Edit the xspec.rc file to contain the line: lmod xwind /path/to/XWIND/src where /path/to/XWIND/src is the full path to the source code (i.e what you get by typing pwd within the XWIND/src directory).

Model Descrption

Within XWIND there are three submodels. These are: xwindline, xwindconv, and xwindfe. Note, while a breif overview of parameters is given here, for a full model desciption including a more physical meaning of each parameter, see Hagen et al. (2026, submitted to A&A)

xwindline

The base model. This simply focuses on the line-shape as given by a wind. As such the res-frame energy is treated as a free-parameter, and the rest-frame emission is considered a simple delta-function.

Par 1. $\log_{10} \dot{m}_{w}$
▸ Units: $\dot{M}_{w} / \dot{M}_{\rm{Edd}}$
▸ Description: Wind mass-outflow rate, scaled by the Eddington accretion rate

Par 2. $r_{\rm{in}} $
▸ Units: $R_{G}$
▸ Description: Inner launch radius

Par 3. $r_{\rm{out}} $
▸ Units: $R_{G}$
▸ Description: Outer launch radius

Par 4. $d_{f}$
▸ Units: $R_{G}$
▸ Description: Distance from origin to wind focus (see Fig. 1 in Hagen et al. 2026)

Par 5. $f_{\rm{cov}}$
▸ Units: $\frac{\Omega}{4 \pi}$
▸ Description: Covering fraction fo the wind as seen from the central (illuminating) source

Par 6. $\log_{10} v_{\infty}$
▸ Units: $c$
▸ Description: Outflow velocity at infinity

Par 7. $r_{v}$
▸ Units: $R_{G}$
▸ Description: Velocity scale length. i.e. The distance along the streamline where the wind reaches half $v_{\infty}$

Par 7. $\beta$
▸ Units: Dimensionless
▸ Description: Wind velocity exponent. Determines the acceleration along a streamline

Par 8. $v_{\rm{turb}}$
▸ Units: km/s
▸ Description: Turbulents velocity. Assumed constant throughout the wind. Sets the width of the Gaussian smoothing kernel used to emulate tubulence

Par 9. $\kappa$
▸ Units: Dimensionless
▸ Description: Sets the weighting for wind launching efficiency as function of radius

Par 10. Inc.
▸ Units: Degrees
▸ Description: Observer inclination (measured from the z-axis)

Par 11. $E_{0}$
▸ Units: keV
▸ Description: Rest frame line energy

Par 12. Norm
▸ Units: photons/s/cm$^2$
▸ Description: Normalisation. Sets the total number of photons within the line

xwindconv

Convolution model. This takes the line profiles from xwindline and uses them as a convolution kernel that is then applied to an input spectrum. This can then be used on a series of lines or continuum. Note, the internal normalisation is set to conserve photon number. i.e. If the input spectrum being convolved contains 100 photons, then the output specturm will also contain 100 photons.