def METHOD_NAME(self, dataset):
    """Estimate minimum excess to reach the given significance.
    Parameters
    ----------
    dataset : `SpectrumDataset`
        Spectrum dataset
    Returns
    -------
    excess : `RegionNDMap`
        Minimal excess
    """
    n_off = dataset.counts_off.data
    stat = WStatCountsStatistic(
        n_on=dataset.alpha.data * n_off, n_off=n_off, alpha=dataset.alpha.data
    )
    excess_counts = stat.n_sig_matching_significance(self.n_sigma)
    is_gamma_limited = excess_counts < self.gamma_min
    excess_counts[is_gamma_limited] = self.gamma_min
    bkg_syst_limited = (
        excess_counts < self.bkg_syst_fraction * dataset.background.data
    )
    excess_counts[bkg_syst_limited] = (
        self.bkg_syst_fraction * dataset.background.data[bkg_syst_limited]
    )
    excess = Map.from_geom(geom=dataset._geom, data=excess_counts)
    return excess