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In recent years, thanks to new facilities such as LOFAR capable of sensitiveobservations, much work has been done on the detection of stellar radioemission at low frequencies. Such emission has commonly been shown to becoherent emission, generally attributed to electron-cyclotron maser emission,and has usually been detected from main-sequence M dwarfs. Here we report thefirst detection of coherent emission at low frequencies from T Tauri stars,which are known to be associated with high levels of stellar activity. UsingLOFAR, we have detected several bright radio bursts at 150 MHz from twoweak-line T Tauri stars: KPNO-Tau 14 and LkCa 4. All of the bursts have highbrightness temperatures ($10^{13} - 10^{14}\ \mathrm{K}$) and high circularpolarization fractions (60 - 90 \%), indicating that they must be due to acoherent emission mechanism. This could be either plasma emission orelectron-cyclotron maser (ECM) emission. Due to the exceptionally highbrightness temperatures seen in at least one of the bursts ($\geq 10^{14}\\mathrm{K}$), and the high circular polarization levels, it seems unlikely thatplasma emission could be the source and so ECM is favoured as the most likelyemission mechanism. Assuming this is the case, the required magnetic field inthe emission regions would be 40 - 70 G. We determine that the most likelymethod of generating ECM emission is plasma co-rotation breakdown in thestellar magnetosphere. There remains the possibility, however, it could be dueto an interaction with an orbiting exoplanet.

Detection of coherent low-frequency radio bursts from weak-line TTauri stars