4.1.12. Dust: dust scattering modelΒΆ

This model calculates the effective transmission of dust that scatters photons out of the line of sight. No re-emission is taken into account, i.e. it is assumed that all scattered photons are lost from the line of sight. This makes the model useful for instruments with a high spatial resolution (i.e, the spatial resolution is much better than the typical size of the dust scattering halo).

Dust scattering is described for example by Draine et al. (2003) In that paper, a link is given to the website of Draine. This website contains slightly updated cross sections for three cases as listed below. The scattering is computed for a Carbonaceous - Silicate Model for Interstellar Dust. The cases are:

  1. set=1: for R_V=3.1;

  2. set=2: for R_V=4.0;

  3. set=3: for R_V=5.5.


For any instrument where the extraction region has a size comparable to the size of the dust scattering halo, this model should not be used, as the scattered X-rays will fall within the extraction region. Take care when fitting data from different instruments simultaneously.


This model only calculates the dust scattering, not the dust absorption.

The parameters of the model are:

nh : Hydrogen column density in 10^{28} \mathrm{m}^{-2}. Default value: 10^{-4} (corresponding to 10^{24} \mathrm{m}^{-2}, a typical value at low Galactic latitudes).
f : The covering factor of the absorber. Default value: 1 (full covering)
set : The set of cross sections being used. See table above.

Recommended citation: Draine et al. (2003).