Here we specify two formats for the background template models (see bkg
) of a full-enclosure IRF:
BKG_2D
models depend onENERGY
andTHETA
, i.e. are radially symmetric.BKG_3D
models depend onENERGY
and field of view coordinatesDETX
andDETY
.
The BKG_2D
format contains a 2-dimensional array of post-select background rate, stored in the fits-arrays-bintable-hdu
format.
ENERG_LO
,ENERG_HI
-- ndim: 1, unit: TeV- Reconstructed energy axis
THETA_LO
,THETA_HI
-- ndim: 1, unit: deg- Field of view offset axis (see
coords-fov
).
- Field of view offset axis (see
BKG
-- ndim: 2, unit: s^-1 MeV^-1 sr^-1- Absolute post-select background rate (expected background per time, energy and solid angle).
Recommended axis order: ENERGY
, THETA
As explained in hduclass
, the following header keyword should be used to declare the type of HDU:
HDUDOC
= 'https://github.com/open-gamma-ray-astro/gamma-astro-data-formats'HDUVERS
= '0.3'HDUCLASS
= 'GADF'HDUCLAS1
= 'RESPONSE'HDUCLAS2
= 'BKG'HDUCLAS3
= 'FULL-ENCLOSURE'HDUCLAS4
= 'BKG_2D'
Example data file: here <./bkg_2d_full_example.fits>
.
The BKG_3D
format contains a 3-dimensional array of post-select background rate, stored in the fits-arrays-bintable-hdu
format.
ENERG_LO
,ENERG_HI
-- ndim: 1, unit: TeV- Reconstructed energy axis
DETX_LO
,DETX_HI
,DETY_LO
,DETY_HI
-- ndim: 1, unit: deg- Field of view coordinates binning (see
coords-fov
)
- Field of view coordinates binning (see
BKG
-- ndim: 3, unit: s^-1 MeV^-1 sr^-1- Absolute post-select background rate (expected background per time, energy and solid angle).
Recommended axis order: ENERGY
, DETX
, DETY
As explained in hduclass
, the following header keyword should be used to declare the type of HDU:
HDUDOC
= 'https://github.com/open-gamma-ray-astro/gamma-astro-data-formats'HDUVERS
= '0.3'HDUCLASS
= 'GADF'HDUCLAS1
= 'RESPONSE'HDUCLAS2
= 'BKG'HDUCLAS3
= 'FULL-ENCLOSURE'HDUCLAS4
= 'BKG_3D'
Further header keywords:
FOVALIGN
= 'ALTAZ' / 'RADEC'- Alignment of the field-of-view coordinate system (see
coords-fov
)
- Alignment of the field-of-view coordinate system (see
Example data file: here <./bkg_3d_full_example.fits>
.
The background rate is not a "flux" or "surface brightness". It is already a count rate, it doesn't need to be multiplied with effective area to obtain predicted counts, like gamma-ray flux and surface brightness models do. The rate is computed per observation time (without any dead-time correction, don't use livetime when computing or using the background rate).