Top left panel: detection significances achievable on the entire sky by the omni-directional instruments on board INTEGRAL, together with those of the IBIS/ISGRI and IBIS/PICsIT (see Fig. 4 for a more detailed description of the imaging instrument sensitivity for observations within their FoVs). The detection significances have been normalized to the maximum value that can be obtained by the SPI-ACS in the most favorable orientation and considering a 1 s event whose emission is characterized by a Comptonized spectral model with α = −0.5 and Ep = 600 keV. A shaded region is drawn for each instrument to represent how the detection significances change at different zenith angles (explicitly marked on the figure axes), also taking into account the dependence of the instrument sensitivity as a function of the azimuthal angles (not explicitly indicated in the figure). For each zenith angle, we computed the distribution of the significances for all relevant azimuthal angles; for clarity, we excluded from the shaping of the shaded regions the 10% worst and 10% best values. The satellite pointing direction is toward zenith angle 0 deg, while the axis pointing from SPI to IBIS is along the 90 deg direction. Top right panel: same as top left, but for an 8 s event whose emission is characterized by a Band spectral model (Band et al. 1993) with α = −1, Ep = 300 keV, and β = −2.5. Bottom panel: sketch of INTEGRAL derived from the INTEGRAL mass model (TIMM) showing the satellite pointing direction (zenith angle 0 deg), the axis connecting SPI to IBIS (zenith angle 90 deg), and the location of the different instruments.
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