docs: def _load_data(self, band):
          """From the WISE All-Sky Explanatory Supplement, IV.4.h.i.1, and Jarrett+
          2011. These are relative response per erg and so can be integrated
          directly against F_nu spectra. Wavelengths are in micron,
          uncertainties are in parts per thousand.
  
          """
          # `band` should be 1, 2, 3, or 4.
          df = bandpass_data_frame('filter_wise_' + str(band) + '.dat', 'wlen resp uncert')
          df.wlen *= 1e4 # micron to Angstrom
          df.uncert *= df.resp / 1000. # parts per thou. to absolute values.
          lo, hi = self._filter_subsets[band]
          df = df[lo:hi] # clip zero parts of response.
          return df