Improved Reduction Algorithm for ISOPHOT-S Chopped Observations

Abstract

The astronomical data gathered by the extrinsic photoconductors on-board the ISO satellite were greatly affected by the high energy radiation environment in space. In addition so called transients with long time constants make automated pipeline processing of the data a challenge. ISOPHOT-S is the high sensitivity spectrometer of the ISOPHOT instrument, featuring two 64 element Si:Ga arrays for the wavelength range of 2.5 to 11.6 microns. It collected a wealth of almost 300 observations of extragalactic nuclei at a spectral resolution of ~100. Most of those observations were performed using the chopped observing mode, justifying a dedicated effort to revise and improve the automatic processing techniques in order to derive a homogeneously reduced dataset with realistic uncertainties. The improvements compared to the original standard pipeline processing include techniques like ramp subdivision, smoothed sigma kappa deglitching, spike filtering and accounting for a non-Gaussian signal distribution due to the glitch residuum.