code: def sum_over_energy(self):
          
          # Note that the array is using the opposite convention from WCS
          # so we sum over axis 0 in the array, but drop axis 2 in the WCS object
          return Map(np.sum(self.counts, axis=0), self.wcs.dropaxis(2))
docs: Reduce a 3D counts cube to a 2D counts map