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.

Warning

Do not confuse \sigma with FWHM 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 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).