GammaLib

I have effective area data saved to a fits file ('EFFECTIVE AREA’, columns: ENERG_LO, ENERG_HI, THETA_LO, THETA_HI, EFFAREA, EFFAREA_RECO), and read in to a GObservation via GCTAAeff2D().

When I then get the effective area from the GObservations object, at different energies and theta offsets (from camera center), the interpolation works fine within the bounds of the given fits file (the green box in the attached plot). But, when you ask for the effective area where both the energy and offset are higher (the red box in the plot) than the ones given in the fits file, the interpolation starts to return very high, incorrect values. The further in energy/offset you go, the higher the incorrect values become.

Here’s the code I used to get the effective area:

import gammalib

obs = load_runs() # custom loading function, loads event lists/irfs from fits files, returns GObservations() object

# pick energy range and # of bins
energy_min, energy_max = gammalib.GEnergy(), gammalib.GEnergy()
nenergy = 15
energy_min.GeV( 1.0)
energy_max.TeV(50000.0) # way larger than normal

# pick theta offset range and # of bins
ntheta, theta_min, theta_max = 15, 0.0, 3.5 # 3.5 also way larger than normal

# bin widths
edelta = ( energy_max.log10TeV() - energy_min.log10TeV() ) / nenergy
thetadelta = ( theta_max - theta_min ) / ntheta

# get the first observation
run = gammalib.GCTAObservation( obs[0] )        

# loop over each bin in each theta/energy axis, 
# and get the effective area at the bin center
for i in range(nenergy) :
  en = ( (i+0.5) * edelta ) + energy_min.log10TeV()
  for j in range(ntheta) :
    th = ( (j+0.5) * thetadelta ) + theta_min

    # get the effective area
    eff = run.response().aeff()( en, th*gammalib.deg2rad) # cm^2
    print 'en=%f log10(TeV)    theta=%f deg    effarea=%fcm^2' % ( en, th, eff )

I recognize that fov’s and energies that large aren’t physically possible with current-gen detectors, and I’m not sure if there’s some checks to prevent accessing this region of the parameter space, but I thought I should post an issue about it, since that area should return 0.0 .