Transient correction of the LW-ISOCAM data for low contrasted illumination

The detector of the Long Wavelength chan- nel of the ISOCAM camera on-board the Infrared Space Observatory (ISO) presents systematic memory eects of the response which can bias the photometry by a factor as high as 40%. We show that, for uniform illumination, the non linear model developed by Fouks and Schubert (1995) for the detector of PHT-S channel of the ISOPHOT in- strument allows us to describe the LW-ISOCAM response to upward and downward steps of flux with an accuracy better than 1%. For each pixel of the detector, only two parameters have to be used. These parameters are con- stant over the whole life of ISO. On the other hand, spatial variations from pixel to pixel are signicant. We present an inversion method of the Fouks-Schubert model. Without any tting and for low contrasted illumi- nation, data are corrected with a photometric accuracy of 1%, which is typically ten times better than previous methods. We suggest that the same approach could be used for others ISO detectors, and in the future for other experiments.