Coherent radio bursts from known M-dwarf planet host YZ Ceti

Abstract

Observing magnetic star-planet interactions (SPI) offers promise for determining magnetic fields of exoplanets. Models of sub-Alfv\'enic SPI predict that terrestrial planets in close-in orbits around M~dwarfs can induce detectable stellar radio emission, manifesting as bursts of strongly polarized coherent radiation observable at specific planet orbital positions. We present 2-4 GHz detections of coherent radio bursts on the slowly-rotating M dwarf YZ Ceti, which hosts a compact system of terrestrial planets, the innermost orbiting with a 2-day period. Two coherent bursts occur at similar orbital phases of YZ Cet b, suggestive of an enhanced probability of bursts near that orbital phase. We model the system's magnetospheric environment in the context of sub-Alfv\'enic SPI and determine that YZ Ceti b can plausibly power the observed flux densities of the radio detections. However, we cannot rule out stellar magnetic activity, without a well characterized rate of non-planet-induced coherent radio bursts on slow rotators. YZ Ceti is therefore a candidate radio SPI system, with unique promise as a target for the long-term monitoring.