Effective area format¶
Here we specify the format to store the effective area (see Effective Area) of a full-enclosure IRF. It is possible to store as a function of the true energy or as a function of the reconstructed energy.
AEFF_2D¶
Effective Area vs true energy¶
The effective area as a function of the true energy and offset angle is saved as a BINTABLE HDU with required columns listed below.
Columns:
ENERG_LO
,ENERG_HI
– ndim: 1, unit: TeV- True energy axis
THETA_LO
,THETA_HI
– ndim: 1, unit: deg- Field of view offset axis
EFFAREA
– ndim: 2, unit: m^2- Effective area value as a function of true energy
Recommended axis order: ENERGY
, THETA
Header keywords:
If the IRFs are only known to be “valid” or “safe” to use within a given energy range, that range can be given via the following two keywords. The keywords are optional, not all telescopes use the concept of a safe range; e.g. in CTA at this time this hasn’t been defined. Note that a proper scheme to declare IRF validity range (e.g. masks or weights, or safe cuts that depend on other parameters such as FOV offset) is not available yet.
LO_THRES
type: float, unit: TeV- Low energy threshold
HI_THRES
type: float, unit: TeV- High energy threshold
If the effective area corresponds to a given observation with an OBS_ID
,
that OBS_ID
should be given as a header keyword. Note that this is not
always the case, e.g. sometimes IRFs are simulated and produced for instruments
that haven’t even been built yet, and then used to simulate different kinds of
observations.
As explained in HDU classes, 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
= ‘0.2’HDUCLASS
= ‘GADF’HDUCLAS1
= ‘RESPONSE’HDUCLAS2
= ‘EFF_AREA’HDUCLAS3
= ‘FULL-ENCLOSURE’HDUCLAS4
= ‘AEFF_2D’
The recommended EXTNAME
keyword is “EFFECTIVE AREA”.
Effective Area vs reconstructed energy¶
The effective area as a function of the reconstructed energy, may be stored as
an additional HDU within the FITS file. Note in this case, the ENERG_LO
and ENERG_HI
columns
contain the reconstructed energy instead of the true energy.
The format is analog to the one described in aeff_2d
, except for the HDUCLAS4
keyword:
HDUCLAS4
= ‘AEFF_2D_RECO’
The EXTNAME
keyword is recommended to be “EFFECTIVE AREA (RECO)”.
Example data file: here
.