  We investigate the possible nonlinear variability properties of the black
hole X-ray nova 4U1543-47 to complement the temporal studies based on linear
techniques, and to search for signs of nonlinearity in Galactic black hole
(GBH) light curves. First, we apply the weighted scaling index method (WSIM) to
characterize the X-ray variability properties of 4U1543-47 in different
spectral states during the 2002 outburst. Second, we use surrogate data to
investigate whether the variability is nonlinear in any of the different
spectral states. The main findings can be summarized as follows. The mean
weighted scaling index appears to be able to parametrize uniquely the temporal
variability properties of this GBH: the 3 different spectral states of the 2002
outburst of 4U1543-47 are characterized by different and well constrained
values. The search for nonlinearity reveals that the variability is linear in
all light curves with the notable exception of the very high state. Our results
imply that we can use the WSIM to assign a single number, namely the mean
weighted scaling index, to a light curve, and in this way discriminate among
the different spectral states of a source. The detection of nonlinearity in the
VHS, that is characterized by the presence of most prominent QPOs, suggests
that intrinsically linear models which have been proposed to account for the
low frequency QPOs in GBHs may be ruled out (abridged).
