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Please note: this code is old and would need considerable updates for
modern Xspec versions. It is provided as-is.

resfree 0.21

see: Sanders & Fabian (2006)
     Off-centre abundance peaks and resonance scattering in clusters
     of galaxies

Please email me for help.

This is an xspec model for fitting spectra from clusters including
resonance scattering.

In the version here, up to 16 annuli can be fit, with multiple
datasets per annulus. This value can be increased (see below).

There is one change from the version of the model described in the
paper. If interpolation is used, the log of the temperature and
density are interpolated in log radius, rather than the temperature
and density themselves.

Compiling the model
Here are instructions on compiling the model with xspec11. I have only
tested the model on xspec11.3.1 under Fedora Core 2 linux/RHEL4 (x86, and
x86-64). For details on compiling local models in xspec see:

Basically, you should (this is using linux):

1. Unpack this distribution somewhere sensible
2. You need to edit the file resfree.h
   The directory DATABASEDIR needs to be edited to contain the
   directory you've just unpacked. DON'T FORGET THIS STEP!!
   You also need to set XSPECDATADIR to where xspec stores the apec
   data files. You may need to change the APECVERSION, but this should
   be the same as aped_resonance_lines.dat was generated with.
3. Do (using tcsh):

> (do what you need to do to setup xantools/xspec)
> setenv LMODDIR /path/to/where/this/model/is/
> cd $LHEASOFT/../spectral/xspec/src/local_mod
> hmake

You can now work on your spectra in xspec if this worked. You need to
set LMODDIR and LD_LIBRARY_PATH each time you use the model before
running xspec.

Using the model
The model is a little unconventional compared to other xspec
models. This is because it needs to know the norm of the model is
fixed in order to compute the true physical density of the gas.

Typically in xspec you would use:

XSPEC>model phabs(resfree)

There are quite a lot of parameters. Using this model syntax, they

1:     nH: absorption to apply to entire resonace scattering model (phabs)
2-17:  ne1-ne16: physical electron density in each shell, inside to outside
       you need to thaw those parameters for the shells you have
       For instance if you have 6 shells, thaw 2-7
18-33: kT1-kT16: temperature for each shell (thaw only those appropriate)
34-49: Z1-Z16: abundance (rel to solar) for each shell (thaw only those
50-65: nH1-nH16: absorption, nH, per unit volume, in units of
       10^22 cm^-2 kpc^-1 in each shell. The model is much faster with these
       set to 0.
66:    scatout: whether to include the effect of resonance scattering out of
       the line of sight. 0 is off, 1 is on. You probably want to
       set parameter 51 to the same value.
67:    scatin: whether to include the effect of resonance scattering
       into the line of sight. 0 is off, 1 is on. This parameter only
       works if scatout is set to 1.
68:    subshell: the number of subshells included within each
       shell. This is n_s in the paper. More gives more accurate
       results, but you may not see much difference beyond
       3. Increasing this number slows down the model a lot.
69:    redshift: redshift of the cluster. This needs to be set
       correctly as the model uses this to work out the distance to
       the cluster, and so calculate the physical electron density. It
       uses the current xspec cosmology to do this.
70:    turb: additional turbulent velocity component. Increase this
       value (in km/s), to add an additional turbulent component to
       the line widths. This is v_turb in the paper. Increasing this
       value typically decreases the effect of resonance scattering.
71:    inner: the inner radius of the inner shell in
       arcseconds. Remember to set this if you miss out the centre of
       the cluster!!
72:    interpol: whether to interpolate the temperature, density, and
       abundance from the centre of the shells in the subshells. If
       this is set to 1, then interpolation is used, otherwise there
       is a fixed ne, Z and kT within each shell. Experience indicates the
       results are less stable with this enabled.

To use the model, you need to add two header keywords to each
spectrum (this is a bit like projct).

You need to set
XFLT0001 = outer radius of annulus in _arcseconds_
XFLT0002 = degrees the annulus occupies (360 for a full circle)

You load the spectra in as a single datagroup (in radial order, outwards):

XSPEC> data ann1.spec ann2.spec ann3.spec ....

You can supply multiple spectra for each annulus, if you set the
XFLT0001 parameter to be the same for each spectrum for the same
region. The XFLT0002 parameters can be different, however. You need to
put the spectra for the same annulus together, e.g.

XSPEC> data ann1_ds1.spec ann1_ds2.spec ann2_ds1.spec ann2_ds2.spec ...

The model prints out how many annuli and datasets you have loaded, so
it's a good idea to check these values.

 o Make sure you know what cosmology xspec is using before using the model.
 o Freeze the norm parameter to 1 straight away after defining the model in
   case you forget.
 o Remember to set the inner radius and redshift parameters straight
 o Set parameters 66 and 67 to 1 to include resonance scattering
 o In my experience the best way to get a fast fit is:
     - Set N_H to an appropriate value, and thaw
     - Set all the T parameters to the average temperature of the cluster
     - Thaw all the appropriate ne parameters
     - Fit
     - Thaw all the appropriate T parameters
     - Fit
     - Thaw all the appropriate Z parameters
     - Fit
     - (optionally thaw absorption parameters, fit)
 o You probably want to calculate all the errors. I've got a useful
   script to do this:

  XSPEC> source common.tcl
  XSPEC> source profile_errors.tcl
  XSPEC> profile_errors out.qdp 2 18 34

  This will dump the density, temperature and abundance profiles,
  using the XFLT0001 parameters to calculate the physical radius in
  kpc. You can then plot the file in qdp.

Increasing the maximum number of shells to fit
You probably don't want to do this, but you can increase the number of
shells by:

o Change PARAMS_NOSHELLS in resfree.h to a larger number
o Edit lmodel.dat, and add extra parameters for ne, kT and Z as
o Recompile from scratch (delete all *.o *.so *.a)
o Be aware all the parameter numbers will change!

Using a new version of APED/ATOMDB
If a new version of APED/ATOMDB comes along, you can recreate the
resonance line database using the script. To
do this you need the following Python modules installed:

o numarray:

You need to edit the script to edit the
location of the atomdb directory (see the top of the file). You can
then run the script

> python


Resonance scattering model for Xspec



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