  We present constraints on the non-linear coupling parameter fnl with the
Wilkinson Microwave Anisotropy Probe (WMAP) data. We use the method based on
the spherical Mexican hat wavelet (SMHW) to measure the fnl parameter for three
of the most interesting shapes of primordial non-Gaussianity: local,
equilateral and orthogonal. Our results indicate that this parameter is
compatible with a Gaussian distribution within the two sigma confidence level
(CL) for the three shapes and the results are consistent with the values
presented by the WMAP team. We have included in our analysis the impact on fnl
due to contamination by unresolved point sources. The point sources add a
positive contribution of Delta(fnl) = 2.5 \pm 3.0, Delta(fnl) = 37 \pm 18 and
Delta(fnl) = 25 \pm 14 for the local, equilateral and orthogonal cases
respectively. As mentioned by the WMAP team, the contribution of the point
sources to the orthogonal and equilateral form is expected to be larger than
the local one and thus it cannot be neglected in future constraints on these
parameters. Taking into account this contamination, our best estimates for fnl
are -16.0 \leq fnl \leq 76.0, -382 \leq fnl \leq 202 and -394 \leq fnl \leq 34
at 95% CL for the local, equilateral and orthogonal cases respectively. The
three shapes are compatible with zero at 95% CL (2{\sigma}). Our conclusion is
that the WMAP 7-year data are consistent with Gaussian primordial fluctuations
within ~2{\sigma} CL. We stress however the importance of taking into account
the unresolved point sources in the measurement of fnl in future works,
especially when using more precise data sets such as the forthcoming Planck
data.
