gabs: gaussian absorption line

$$M(E) = exp\left(-\left(par3/(\sqrt{2\pi}par2)\right) exp\left(-.5\left(\left(E-par1\right)/par2\right)^2\right)\right)$$

where:

par1 = line energy in keV.

par2 = line width (sigma) in keV.

par3 = line depth in keV. The optical depth at line center is par3/par2/$\sqrt{2\pi}$.