2025MNRAS.544.1220P

The unambiguous detection of magnetic star-planet interaction (SPI) via radio observations would provide a novel method for detecting exoplanets and probing their magnetic fields. Although direct radio detection of sub-Jovian planets is hindered by the low frequencies involved, models of sub-Alfvénic SPI predict that Earth-like planets in close-in orbits around M dwarfs may induce detectable emission. Here, we revisit the modelling of the expected radio emission from magnetic star-planet interaction in the iconic M-dwarf systems Proxima Centauri, YZ Ceti, and GJ 1151, where claims of SPI-related radio detections have been made. For this, we use SIRIO (Star-planet Interaction and Radio Induced Observations), a public PYTHON code that models radio emission from sub-Alfvénic SPI. We benchmark SIRIO results against those paradigmatic systems, whose SPI modelling has been previously discussed in the literature. Our results support previous findings that Proxima b, YZ Cet b, and the putative planet GJ 1151 b are most likely in the sub-Alvénic regime (assuming a hybrid potential field source surface geometry), so SPI should be at work in all of them. We find that the Alfvén wing model generally predicts a very low level of radio emission, while if magnetic reconnection takes place, prospects for detection are significantly better. We also find that free-free absorption may play a relevant role, in particular in YZ Ceti. Our SIRIO code can also be used to evaluate the feasibility of radio proposals aimed at detecting SPI, and to constrain the stellar wind mass-loss rate or planetary magnetic field.