  We present a Gaussianity analysis of the WMAP 5-year Cosmic Microwave
Background (CMB) temperature anisotropy data maps. We use several third order
estimators based on the spherical Mexican hat wavelet. We impose constraints on
the local non-linear coupling parameter fnl using well motivated non-Gaussian
simulations. We analyse the WMAP maps at resolution of 6.9 arcmin for the Q, V,
and W frequency bands. We use the KQ75 mask recommended by the WMAP team which
masks out 28% of the sky. The wavelet coefficients are evaluated at 10
different scales from 6.9 to 150 arcmin. With these coefficients we compute the
third order estimators which are used to perform a chi-squared analysis. The
chi-squared statistic is used to test the Gaussianity of the WMAP data as well
as to constrain the fnl parameter. Our results indicate that the WMAP data are
compatible with the Gaussian simulations, and the fnl parameter is constrained
to -8 < fnl < +111 at 95% CL for the combined V+W map. This value has been
corrected for the presence of undetected point sources, which add a positive
contribution of Delta_fnl = 3+-5 in the V+W map. Our results are very similar
to those obtained by Komatsu et al (2008) using the bispectrum.
