def make_energy_bounds_hdu(self, extname="EBOUNDS"):
        """ Builds and returns a FITs HDU with the energy bin boundries

        extname   : The HDU extension name            
        """
        if self._ebins is None:
            return None
        cols = [fits.Column("CHANNEL", "I", array=np.arange(1, len(self._ebins + 1))),
                fits.Column("E_MIN", "1E", unit='keV',
                            array=1000 * self._ebins[0:-1]),
                fits.Column("E_MAX", "1E", unit='keV', array=1000 * self._ebins[1:])]
        hdu = fits.BinTableHDU.from_columns(
            cols, self.make_header(), name=extname)
        return hdu
Builds and returns a FITs HDU with the energy bin boundries

        extname   : The HDU extension name