# 4.1.17. Gaus: gaussian line model¶

The Gaussian line model is the simplest model for a broadened emission line.

The spectrum is given by:

where is the photon energy in keV, the photon flux in units of ph , is the average line energy of the spectral line (in keV) and is the line normalisation (in units of ph ). The total line flux is simply given by . Further is the Gaussian width, which is related to the full width at half maximum by or approximately .

To ease the use for dispersive spectrometers (gratings) there is an
option to define the wavelength instead of the energy as the basic
parameter. The parameter *type* determines which case applies: type=0
(default) corresponding to energy, type=1 corresponding to wavelength
units.

Warning

Do not confuse with when interpreting your fit results with other data.

Warning

When changing from energy to wavelength units, take care about the frozen/thawn status of the line centroid and FWHM.

Warning

You need to do a `calc`

or `fit`

command to get an update
of the wavelength (for type=0) or energy (type=1).

The parameters of the model are:

`norm`

: Normalisation , in units of
ph . Default value: 1.`e`

: The line energy in keV. Default value: 6.4 keV.`fwhm`

: The line , in keV.`type`

: The type: 0 for energy units, 1 for wavelength units.`w`

: The line wavelength in Å. Default value: 20 Å.`awid`

: The line , in Å.*Recommended citation:* Gauss (1809).