def free_index(self, name, free=True, **kwargs):
        """Free/Fix index of a source.

        Parameters
        ----------

        name : str
            Source name.

        free : bool
            Choose whether to free (free=True) or fix (free=False).

        """
        src = self.roi.get_source_by_name(name)
        self.free_source(name, free=free,
                         pars=index_parameters.get(src['SpectrumType'], []),
                         **kwargs)