Voigt function (Gamma is HWHM or FWHM)

I have a very simple question , in ROOT I am trying to fit voigt distribution using TF1 *voigtFit = new TF1(“voigtFit”, “[0]*TMath::Voigt(x - [1], [2], [3])”
and I am getting
Fitted Parameters:
Amplitude: 6268.05
Mean: -3.5849
Sigma (Gaussian): 0.227483
Gamma (Lorentzian): 0.64189
I want to know if Gamma is HWHM or FWHM?
Thanks in advance

_ROOT Version:_6.24/06
Platform: Ubuntun 18
Compiler: linuxx8664gcc

Check out the equation: ROOT: TMath Namespace Reference