“…BH spin, inclination, study of accretion disk dynamics, GR effects from polarized thermal disk emission (Dovčiak et al, 2008;Schnittman & Krolik, 2009) ∼1-3 % A few % of PF for Cygnus X-1 in high soft state (Long et al, 1980) IXPE (2021) (Weisskopf et al, 2016;Soffitta, 2017), EXTP (Zhang et al, 2016), SOLPEX (Ste ¸ślicki et al, 2016) Blazars First peak of HBL (faint in this energy range) − Jet structure, magnetic field geometry (Zhang et al, 2014;Tavecchio et al, 2018) a few to high % depending on the B field geometry Magnetars Vacuum birefringence, signature of RICS (Taverna et al, 2014) ∼20 % XRP Emission mechanism, geometry -Polar cap/Outer gap/slot gap/striped wind models (Weisskopf et al, 2009;Harding, 2019) a few tens of % ∼15 % PF for Crab+nebula by PolarLight (Feng et al, 2020) SNR, PWN Particle acceleration process in shocks, magnetic field geometry (Bykov et al, 2009) ∼20-50 % from different regions of SNR ∼19 % PF for Crab nebula by OSO-8 (Weisskopf et al, 1978). ∼14 % PF by PolarLight (Feng et al, 2020) 10−100 keV…”