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:

F(E) = A e^{\displaystyle{(E-E_0)^2/2\sigma^2}},

where E is the photon energy in keV, F the photon flux in units of 10^{44} ph \mathrm{s}^{-1} \mathrm{keV}^{-1}, E_0 is the average line energy of the spectral line (in keV) and A is the line normalisation (in units of 10^{44} ph \mathrm{s}^{-1}). The total line flux is simply given by A. Further \sigma is the Gaussian width, which is related to the full width at half maximum FWHM by FWHM=\sigma \sqrt{\ln 256} or approximately FWHM = 2.3548\sigma.

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.


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


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


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 A, in units of 10^{44} ph \mathrm{s}^{-1}. Default value: 1.
e : The line energy E_0 in keV. Default value: 6.4 keV.
fwhm : The line FWHM, in keV.
type : The type: 0 for energy units, 1 for wavelength units.
w : The line wavelength \lambda in Å. Default value: 20 Å.
awid : The line FWHM, in Å.

Recommended citation: Gauss (1809).