SpectrumDataset

class gammapy.spectrum.SpectrumDataset(models=None, counts=None, livetime=None, aeff=None, edisp=None, background=None, mask_safe=None, mask_fit=None, name='', gti=None)

Bases: gammapy.modeling.Dataset

Spectrum dataset for likelihood fitting.

The spectrum dataset bundles reduced counts data, with a spectral model, background model and instrument response function to compute the fit-statistic given the current model and data.

Parameters

modelsSkyModels

Fit model

countsCountsSpectrum

Counts spectrum

livetimeQuantity

Livetime

aeffEffectiveAreaTable

Effective area

edispEnergyDispersion

Energy dispersion

backgroundCountsSpectrum

Background to use for the fit.

mask_safendarray

Mask defining the safe data range.

mask_fitndarray

Mask to apply to the likelihood for fitting.

namestr

Dataset name.

gtiGTI

GTI of the observation or union of GTI if it is a stacked observation

See also

SpectrumDatasetOnOff, FluxPointsDataset, gammapy.cube.MapDataset

Attributes Summary

data_shape	Shape of the counts data
energy_range	Energy range defined by the safe mask
excess	Excess (counts - alpha * counts_off)
likelihood_type
mask	Combined fit and safe mask
mask_safe
models	Models (gammapy.modeling.models.SkyModels).
parameters	List of parameters (Parameters)
tag

Methods Summary

copy(self)	A deep copy.
create(e_reco[, e_true, region, reference_time])	Creates empty spectrum dataset.
fake(self[, random_state])	Simulate fake counts for the current model and reduced irfs.
npred(self)	Return npred map (model + background)
plot_counts(self[, ax])	Plot predicted and detected counts.
plot_fit(self)	Plot counts and residuals in two panels.
plot_residuals(self[, method, ax])	Plot residuals.
residuals(self[, method])	Compute the spectral residuals.
stack(self, other)	Stack this dataset with another one.
stat_array(self)	Likelihood per bin given the current model parameters
stat_sum(self)	Total statistic given the current model parameters.

Attributes Documentation

data_shape

Shape of the counts data

energy_range

Energy range defined by the safe mask

excess

Excess (counts - alpha * counts_off)

likelihood_type = 'cash'

mask

Combined fit and safe mask

mask_safe

models

Models (gammapy.modeling.models.SkyModels).

parameters

List of parameters (Parameters)

tag = 'SpectrumDataset'

Methods Documentation

copy(self)

A deep copy.

classmethod create(e_reco, e_true=None, region=None, reference_time='2000-01-01')

Creates empty spectrum dataset.

Empty containers are created with the correct geometry. counts, background and aeff are zero and edisp is diagonal.

The safe_mask is set to False in every bin.

Parameters

e_recoQuantity

edges of counts vector

e_trueQuantity

edges of effective area table. If not set use reco energy values. Default : None

regionSkyRegion

Region to define the dataset for.

reference_timeTime

reference time of the dataset, Default is “2000-01-01”

fake(self, random_state='random-seed')

Simulate fake counts for the current model and reduced irfs.

This method overwrites the counts defined on the dataset object.

Parameters

random_state{int, ‘random-seed’, ‘global-rng’, RandomState}

Defines random number generator initialisation. Passed to get_random_state.

npred(self)

Return npred map (model + background)

plot_counts(self, ax=None)

Plot predicted and detected counts.

Parameters

axAxes

Axes object.

Returns

axAxes

Axes object.

plot_fit(self)

Plot counts and residuals in two panels.

Calls plot_counts and plot_residuals.

plot_residuals(self, method='diff', ax=None, **kwargs)

Plot residuals.

Parameters

axAxes

Axes object.

method{“diff”, “diff/model”, “diff/sqrt(model)”}

Normalization used to compute the residuals, see SpectrumDataset.residuals()

**kwargsdict

Keywords passed to CountsSpectrum.plot()

Returns

axAxes

Axes object.

residuals(self, method='diff')

Compute the spectral residuals.

Parameters

method{“diff”, “diff/model”, “diff/sqrt(model)”}

Method used to compute the residuals. Available options are:

• diff (default): data - model

• diff/model: (data - model) / model

• diff/sqrt(model): (data - model) / sqrt(model)

Returns

residualsCountsSpectrum

Residual spectrum

stack(self, other)

Stack this dataset with another one.

Safe mask is applied to compute the stacked counts vector. Counts outside each dataset safe mask are lost.

Stacking is performed in-place.

The stacking of 2 datasets is implemented as follows. Here, \(k\) denotes a bin in reconstructed energy and \(j = {1,2}\) is the dataset number

The mask_safe of each dataset is defined as:

\[\begin{split}\epsilon_{jk} =\left\{\begin{array}{cl} 1, & \mbox{if bin k is inside the energy thresholds}\\ 0, & \mbox{otherwise} \end{array}\right.\end{split}\]

Then the total counts and model background bkg are computed according to:

\[ \begin{align}\begin{aligned}\overline{\mathrm{n_{on}}}_k = \mathrm{n_{on}}_{1k} \cdot \epsilon_{1k} + \mathrm{n_{on}}_{2k} \cdot \epsilon_{2k}\\\overline{bkg}_k = bkg_{1k} \cdot \epsilon_{1k} + bkg_{2k} \cdot \epsilon_{2k}\end{aligned}\end{align} \]

The stacked safe_mask is then:

\[\overline{\epsilon_k} = \epsilon_{1k} OR \epsilon_{2k}\]

Please refer to the IRFStacker for the description of how the IRFs are stacked.

Parameters

otherSpectrumDataset

the dataset to stack to the current one

stat_array(self)

Likelihood per bin given the current model parameters

stat_sum(self)

Total statistic given the current model parameters.