The nature of magnetic activity at the low-mass end of the main-sequence

We propose XMMNewton observations of 4 carefully selected ultracool dwarfs(UCDs), supported by EVLA monitoring, to systematically investigate magneticactivity near the spectral type M/L transition. Our targets are nearby (< 20pc),known to maintain magnetic fields (direct field detections), they yield evidencefor chromospheres (Halpha emission) and have known rotation rate (v sini). Thisallows us to study the connection between chromospheric and coronal activity,their relation with rotation, and possibly study flares at the bottom of themainsequence. In AO11 only two objects, both slowly rotating, were observed.For AO13 we focus on fast rotators. A statistical and unbiased sample is neededto test our hypothesis of two populations of UCDs with distinct radio/Xray/rotation properties. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]