A new method for ISOCAM data reduction -: I.: Application to the European Large Area ISO Survey Southern Field:: method and results

We develop a new data reduction technique for ISOCAM LW data and apply it to the European Large Area ISO Survey (ELAIS) LW3 (15-mum) observations in the southern hemisphere (S1). This method, known as LARI technique and based on the assumption of the existence of two different time-scales in ISOCAM transients (accounting for either fast or slow detector response), is particularly designed for the detection of faint sources. In the ELAIS S1 field we obtain a catalogue of 462 15-mum sources with signal-to-noise ratios greater than or equal to5 and flux densities in the range 0.45-150 mJy (filling the whole flux range between the Deep ISOCAM Surveys and the IRAS Faint Source Survey). The completeness at different flux levels and the photometric accuracy of this catalogue are tested with simulations. Here we present a detailed description of the method and discuss the results obtained by its application to the S1 LW3 data.