In-flight effective areas for the Swift UVOT, as obtained from the CALDB.
        See Breeveld+ 2011. XXX: confirm that these are equal-energy, not
        quantum-efficiency.

def _load_data(self, band):
        """In-flight effective areas for the Swift UVOT, as obtained from the CALDB.
        See Breeveld+ 2011. XXX: confirm that these are equal-energy, not
        quantum-efficiency.

        """
        d = bandpass_data_fits('sw' + self._band_map[band] + '_20041120v106.arf')[1].data

        # note:
        #   data.WAVE_MIN[i] < data.WAVE_MIN[i+1], but
        #   data.WAVE_MIN[i] > data.WAVE_MAX[i] (!)
        #   data.WAVE_MIN[i] = data.WAVE_MAX[i+1] (!)

        wmid = 0.5 * (d.WAVE_MIN + d.WAVE_MAX) # in Ångström
        df = pd.DataFrame({'wlen': wmid, 'resp': d.SPECRESP,
                           'wlo': d.WAVE_MAX, 'whi': d.WAVE_MIN})
        return df