Quasars as standard candles I: The physical relation between disc and coronal emission

E. Lusso, G. Risaliti

A tight non-linear relation exists between the X-ray and UV emission in quasars (i.e. $L_{\mathrm{X}}\propto L_{\mathrm{UV}}^{\gamma }$), with a dispersion of $\sim$0.2~dex over $\sim$3~orders of ma…