Dependence of the normalized torque γΓ∕Γ₀ on the planet mass M_p (top) and α viscosity (bottom). Additionally, the top horizontal axis of each panel shows the position of the outer gap edge r_edge as resulting from Eq. (24). Circles and solid black lines correspond to simulations with gap irradiation; diamonds and dashed grey lines correspond to reference non-radiative simulations. Open symbols correspond to simulations without torque oscillations (i.e. Rossby-stable) while filled symbols mark simulations with gap edge instabilities. Data points are labelled with the corresponding torque reduction factor f_irr (Eq. (35)). Clearly, gap edge irradiation reduces the magnitude of the torque (or even causes torque reversal) for M_p < 1 M_J and α > 10⁻³.