Expected flux density for auroral radio emission arising from a star-planet interaction in the system GJ 1151 – GJ 1151 c as a function of orbital distance. The interaction is clearly in the supra-Alfvénic regime (i.e. Alfvén Mach number ; top panel) at the location of the planet (vertical dashed line). Therefore, star–planet interaction cannot account for the observed LOFAR radio emission. The planet in the bottom panel is drawn at around 0.1 mJy in the y-axis, which corresponds to the 1 σ level of the LOFAR radio observations. See main text for details.