Add note on excess map double correlation
@@ -62,10 +62,19 @@ def convolved_map_dataset_counts_statistics(dataset, kernel, mask, correlate_off
class ExcessMapEstimator(Estimator):
- """Computes correlated excess, sqrt TS (i.e. Li-Ma significance) and errors for MapDatasets.
+ """Computes correlated excess, significance and error maps from a map dataset.
- If a model is set on the dataset the excess map estimator will compute the excess taking into account
- the predicted counts of the model.
+ If a model is set on the dataset the excess map estimator will compute the
+ excess taking into account the predicted counts of the model.
+
+ ..note::
+ By default the excess estimator correlates the off counts as well to avoid
+ artifacts at the edges of the :term:`FoV` for stacked on-off datasets.
+ However when the on-off dataset has been derived from a ring background
+ estimate, this leads to the off counts being correlated twice. To avoid
+ artifacts and the double correlation, the `ExcessMapEstimator` has to
+ be applied per dataset and the resulting maps need to be stacked, taking
+ the :term:`FoV` cut into account.
Parameters
----------
@@ -88,11 +97,11 @@ class ExcessMapEstimator(Estimator):
Default is None so the optionnal steps are not executed.
energy_edges : `~astropy.units.Quantity`
Energy edges of the target excess maps bins.
- apply_mask_fit : Bool
+ apply_mask_fit : bool
Apply a mask for the computation.
A `~gammapy.datasets.MapDataset.mask_fit` must be present on the input dataset
- correlate_off : Bool
- Correlate OFF events in the case of a MapDatasetOnOff. Default is True.
+ correlate_off : bool
+ Correlate OFF events in the case of a `MapDatasetOnOff`. Default is True.
spectral_model : `~gammapy.modeling.models.SpectralModel`
Spectral model used for the computation of the flux map.
If None, a Power Law of index 2 is assumed (default).
