Sensitivity curves for α as a function of the ULDM mass m for the system J1903+0327 (with parameters given in Table E.2) for masses near the resonant one at ω_b = m. Dashed lines account for all the ULDM effects on the parameter Θ′, while the solid lines are obtained neglecting the ULDM effect on all parameters but P_b. Each colour corresponds to a particular random realisation of the parameters 𝜚 and Υ