X-ray activity versus rotation for the full sample, M-, K-, G-, and F-type stars (from top to bottom). Left panels: X-ray luminosity in the energy band 0.2− 2.0 keV versus Kepler P_rot. Right panels: X-ray activity index versus Rossby number. Colours and symbols follow the convention defined in Fig. 10. The stars in the sample of Wright et al. (2011) are shown as small black dots. The solid lines represent the best-fit relations between X-ray emission and rotation period found by Pizzolato et al. (2003) for stellar mass ranges corresponding approximately to spectral types.