The executable ii_shadow_build creates shadowgrams of ISGRI events in the given time (Tbin) and energy (Ebin) ranges. For every shadowgram a corresponding efficiency shadowgram is created. For pixels active during the revolution (switch status ON), efficiency falls into two components and is null for the others: the first factor takes into account the dead time D of the corresponding module MDU; the second factor reflects the efficiency energy dependence, LT, for the lower energy bins due to the low threshold operation limit, such that: Eff[Tbin,Ebin,y,z]= (1-D[Tbin,mdu]) * LT[Ebin,y,z]. It is this value that is given in the shadowgram efficiency maps. The low threshold (LT) correction is performed using the same energy correction of the COR step and an erf function with time-dependent width which reproduces the degradation in energy resolution of the instrument. The position of the low threshold is evolving with time as can be seen in the Fig. 31, with the ISGRI efficiency being lower than 50% below this energy. As an example, for revolutions later than Rev.1000, energies below 22 keV should be ignored.
This executable also applies two different noisy pixel detection techniques. The first one is time-based; it discriminates every pixel for which the scientific SELECT_FLAG equals one (even only once over all the Science Window events). Note: this flag was filled by the executable ibis_isgr_evts_flag. The second method is spectral-based; it discriminates pixels by estimating their spectral deviation from the average ISGRI spectrum. This spectral method can be switched ON/OFF by parameter NoisyDetFlag.
