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Fig. 6


Left: possible constraints on the hard X-ray polarization fraction of Cygnus X-1 for some of the model predictions proposed in literature (see text for details), predicting about 15%, 25%, and 50% polarization in the low hard state (total flux ~1 Crab) and about 55% polarization in the high soft state (total flux ~300 mCrab). Expected errors are shown as shaded regions. Right: feasibility of phase-resolved polarimetry with CZTI for Crab. The top panel shows Crab pulse profile in 100–300 keV. The middle panel shows polarization in 16 phases, as expected from an interpolation of the polarization measured by Integral in four regions of Crab pulse profile. The shaded region represents possible constraints on phase-wise polarization measurement with CZTI for a total exposure time of 1 Ms. The bottom panel shows the required exposure time to determine polarization for all phases with minimum 3 sigma (solid lines) and 5 sigma (dashed lines) confidence levels. It can be seen that with a total exposure time of ~2 Ms, polarization in most of the phases can be constrained with better than 5-sigma confidence.

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