  While most protostellar jets present free-free emission at radio wavelengths,
synchrotron emission has been also proposed to be present in a handful of these
objects. The presence of non-thermal emission has been inferred by negative
spectral indices at centimeter wavelengths. In one case (the HH 80-81 jet
arising from a massive protostar), its synchrotron nature was confirmed by the
detection of linearly polarized radio emission. One of the main consequences of
these results is that synchrotron emission implies the presence of relativistic
particles among the non-relativistic material of these jets. Therefore, an
acceleration mechanism should be taking place. The most probable scenario is
that particles are accelerated when the jets strongly impact against the dense
envelope surrounding the protostar. Here, we present an analysis of radio
observations obtained with the Very Large Array of the Triple Radio Source in
the Serpens star-forming region. This object is known to be a radio jet arising
from an intermediate-mass protostar. It is also one of the first protostellar
jets where the presence of non-thermal emission was proposed. We analysed the
dynamics of the jet as well as the nature of the emission and discuss these
issues in the context of the physical parameters of the jet and the particle
acceleration phenomenon.
