Template spectral model

This model is defined by custom tabular values.

The units returned will be the units of the values array provided at initialization. The model will return values interpolated in log-space, returning 0 for energies outside of the limits of the provided energy array.

The class implementation follows closely what has been done in naima.models.TemplateSpectralModel

Example plot

Here is an example plot of the model:

import numpy as np
from astropy import units as u
import matplotlib.pyplot as plt
from gammapy.modeling.models import (
    Models,
    PowerLawNormSpectralModel,
    SkyModel,
    TemplateSpectralModel,
)

energy_bounds = [0.1, 1] * u.TeV
energy = np.array([1e6, 3e6, 1e7, 3e7]) * u.MeV
values = np.array([4.4e-38, 2.0e-38, 8.8e-39, 3.9e-39]) * u.Unit("MeV-1 s-1 cm-2")
template = TemplateSpectralModel(energy=energy, values=values)
template.plot(energy_bounds)
plt.grid(which="both")

Example of extrapolation

The following shows how to implement extrapolation of a template spectral model:

energy = [0.5, 1, 3, 10, 20] * u.TeV
values = [40, 30, 20, 10, 1] * u.Unit("TeV-1 s-1 cm-2")
template_noextrapolate = TemplateSpectralModel(
    energy=energy,
    values=values,
    interp_kwargs={"extrapolate": False},
)
template_extrapolate = TemplateSpectralModel(
    energy=energy, values=values, interp_kwargs={"extrapolate": True}
)
energy_bounds = [0.2, 80] * u.TeV
template_extrapolate.plot(energy_bounds, label="Extrapolated", alpha=0.4, color="blue")
template_noextrapolate.plot(
    energy_bounds, label="Not extrapolated", ls="--", color="black"
)
plt.legend()

<matplotlib.legend.Legend object at 0x7ff41dd10c40>

Spectral corrections to templates can be applied by multiplication with a normalized spectral model, for example gammapy.modeling.models.PowerLawNormSpectralModel. This operation creates a new gammapy.modeling.models.CompoundSpectralModel

new_model = template * PowerLawNormSpectralModel(norm=2, tilt=0)

print(new_model)

CompoundSpectralModel
    Component 1 : TemplateSpectralModel

    Component 2 : PowerLawNormSpectralModel

type    name     value    unit   error   min max frozen link prior
---- --------- ---------- ---- --------- --- --- ------ ---- -----
          norm 2.0000e+00      0.000e+00 nan nan  False
          tilt 0.0000e+00      0.000e+00 nan nan   True
     reference 1.0000e+00  TeV 0.000e+00 nan nan   True
    Operator : mul

YAML representation

Here is an example YAML file using the model:

model = SkyModel(spectral_model=template, name="template-model")
models = Models([model])

print(models.to_yaml())

components:
-   name: template-model
    type: SkyModel
    spectral:
        type: TemplateSpectralModel
        parameters: []
        energy:
            data:
            - 1000000.0
            - 3000000.0
            - 10000000.0
            - 30000000.0
            unit: MeV
        values:
            data:
            - 4.4e-38
            - 2.0e-38
            - 8.8e-39
            - 3.9e-39
            unit: 1 / (cm2 MeV s)
metadata:
    creator: Gammapy 2.0.dev155+g9309a089d
    date: '2024-12-18T16:14:27.335636'
    origin: null