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vvoigt, zvvoigt: Voigt line profile with widths in km/s

A Voigt line profile with both $\sigma$ and $\gamma$ in km/s. The Voigt profile is the convolution of a Gaussian and a Lorentzian. It can be written as:

$\displaystyle A(E) = K Re[w(z)] / (\sigma(E_l/c)\sqrt{(2\pi)}) $

where $w(z) = exp(-z^2) erfc(-iz)$ is the Faddeeva function, and $z = (E-E_l + i\gamma(E_l/c)/2)/(\sqrt{2}\sigma(E_l/c))$

The parameters are:

par1 $E_l$, line energy in keV
par2 $\sigma$, gaussian line width in km/s
par3 $\gamma$, lorentzian FWHM line width in kms/
Norm $K$, total photons/cm$^{-2}$/s in the line

For zvoigt the parameters are:

par1 $E_l$, line energy in keV
par2 $\sigma$, gaussian line width in km/s
par3 $\gamma$, lorentzian FWHM line width in km/s
par4 $z$, redshift
Norm $K$, total photons/cm$^{-2}$/s in the line

Both the gaussian and lorentzian lines are truncated at the point that the integrated flux under the line is within a critical value of the total flux. This critical value can be changed using xset LINECRITLEVEL. The default critical value is $1.0\times10^{-6}$. Note also that the normalization is defined as the integral over energies greater than zero since negative energies are unphysical.

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