  In exoplanetary systems, the interaction between the central star and the
planet can trigger Auroral Radio Emission (ARE), due to the Electron Cyclotron
Maser mechanism. The high brightness temperature of this emission makes it
visible at large distances, opening new opportunities to study exoplanets and
to search for favourable conditions for the development of extra-terrestrial
life, as magnetic fields act as a shield that protects life against external
particles and influences the evolution of the planetary atmospheres. In the
last few years, we started an observational campaign to observe a sample of
nearby M-type stars known to host exoplanets with the aim to detect ARE. We
observed YZ Ceti with the upgraded Giant Metrewave Radio Telescope (uGMRT) in
band 4 (550-900 MHz) nine times over a period of five months. We detected radio
emission four times, two of which with high degree of circular polarization.
With statistical considerations we exclude the possibility of flares due to
stellar magnetic activity. Instead, when folding the detections to the orbital
phase of the closest planet YZ Cet b, they are at positions where we would
expect ARE due to star-planet interaction (SPI) in sub-Alfvenic regime. With a
degree of confidence higher than 4.37 sigma, YZ Cet is the first extrasolar
systems with confirmed SPI at radio wavelengths. Modelling the ARE, we estimate
a magnetic field for the star of about 2.4 kG and we find that the planet must
have a magnetosphere. The lower limit for the polar magnetic field of the
planet is 0.4 G.
