Note

You are not reading the most up to date version of Gammapy documentation.
Access the latest stable version v1.3 or the list of Gammapy releases.

Point Spatial Model

This model is a delta function centered in lon_0 and lat_0 parameters provided:

$$\phi(lon, lat) = \delta{(lon - lon_0, lat - lat_0)}$$

The model is defined on the celestial sphere in the coordinate frame provided by the user.

If the point source is not centered on a pixel, the flux is re-distributed across 4 neighbouring pixels. This ensured that the center of mass position is conserved.

Example plot

Here is an example plot of the model:

from astropy.coordinates import SkyCoord
from gammapy.maps import WcsGeom
from gammapy.modeling.models import (
    Models,
    PointSpatialModel,
    PowerLawSpectralModel,
    SkyModel,
)

model = PointSpatialModel(lon_0="0.01 deg", lat_0="0.01 deg", frame="galactic",)

geom = WcsGeom.create(
    skydir=SkyCoord("0d 0d", frame="galactic"), width=(1, 1), binsz=0.1
)
model.plot(geom=geom, add_cbar=True)

YAML representation

Here is an example YAML file using the model:

pwl = PowerLawSpectralModel()
point = PointSpatialModel()

model = SkyModel(spectral_model=pwl, spatial_model=point, name="pwl-point-model")
models = Models([model])

print(models.to_yaml())

Out:

components:
-   name: pwl-point-model
    type: SkyModel
    spectral:
        type: PowerLawSpectralModel
        parameters:
        - {name: index, value: 2.0, unit: '', min: .nan, max: .nan, frozen: false,
            error: 0}
        - {name: amplitude, value: 1.0e-12, unit: cm-2 s-1 TeV-1, min: .nan, max: .nan,
            frozen: false, error: 0}
        - {name: reference, value: 1.0, unit: TeV, min: .nan, max: .nan, frozen: true,
            error: 0}
    spatial:
        type: PointSpatialModel
        frame: icrs
        parameters:
        - {name: lon_0, value: 0.0, unit: deg, min: .nan, max: .nan, frozen: false,
            error: 0}
        - {name: lat_0, value: 0.0, unit: deg, min: -90.0, max: 90.0, frozen: false,
            error: 0}