def _density_par(self,dangle,tdisrupt=None):
        """The raw density as a function of parallel angle"""
        if tdisrupt is None: tdisrupt= self._tdisrupt
        dOmin= dangle/tdisrupt
        # Normalize to 1 close to progenitor
        return 0.5\
            *(1.+special.erf((self._meandO-dOmin)\
                                 /numpy.sqrt(2.*self._sortedSigOEig[2])))
The raw density as a function of parallel angle