First detection of variable radio emission originating from the infant planetary system V1298 Tau

Context. V1298 Tau is a very young and magnetically active K1V star that hosts a benchmark multi-planetary system to study planet formation and evolutionary history at the earliest stages. Thanks to the high interest, it has been the target of a multi-wavelength follow-up.Aims. We selected V1298 Tau for a first targeted follow-up at radio frequencies with the Karl G. Jansky Very Large Telescope (JVLA), the upgraded Giant Metrewave Radio Telescope (uGMRT), and the Sardinia Radio Telescope (SRT) to search for emission in the overall frequency range 0.55–7.2 GHz. Detecting radio emission from such a very active star is key to characterising its magnetosphere, allowing us in principle to probe the strength of the coronal magnetic field and plasma density. Methods. Observations were carried out between October 2023 and September 2024: three epochs (total of ∼180 min on-source) with uGMRT band-4 (0.55–0.75 GHz), 12 epochs (total of ∼427 min on-source) with the JVLA using L (1–2 GHz) and C (4.5–6.5 GHz) bands, and three epochs (total of ∼56 min on-source) with SRT using C-high band (6–7.2 GHz). Results. We report the first detection of radio emission from V1298 Tau at different epochs using the JVLA. The emission has maximum peak flux densities of 91±10 and 177±6 µJy/beam in the L- and C-band, respectively. From a comparison with contemporary optical photometry, we found that the detected emission with the highest fluxes are located around a phase of minimum of the photospheric light curve. Although the uGMRT and SRT observations could not detect the source, we measured 3σ flux density upper limits in the range ∼41–56 µJy/beam using uGMRT, while with SRT we reached upper limits down to 13 mJy. The lack of a significant fraction of circular polarisation indicates that the observed flux is not due to electron cyclotron maser emission from star-planet interaction, and it is likely produced by gyrosynchroton and/or cyclotron emission from the corona triggered by stellar magnetic activity, although we cannot exclude thermal emission, due to a lack of constraints on the brightness temperature.