PSF photometry zero point is off compared to aperture

[jorgemarpa]

The PSF photometry is always a factor ~1.3 above the level of the aperture photometry (see figure) and it matches with the ratio between aperture flux and Gaia flux.
Note: Gaia flux values are used as prior to solve the linear model.

Figure: Comparison of mean photometry between different methods. X-axis is Kepler pipeline aperture photometry (PDCSAP). Y-axis is the ratio between "method" and PDCSAP, with "method" one of: psfmachine-aperture (blue), psfmachine-psf (orange), and Gaia G flux value (green).

We have to estimate this zero-point factor across channels to then consider correcting the PSF absolute flux or save the normalized light curves.