Spin-down comma dynamos comma and habitability\: XMM and K2 exploration of nearby M dwarfs

The rotationactivity relation of M dwarfs is of high astrophysical interest dueto (i) the predicted dynamo transition at the fully convective boundary (SpT virgulM3), (ii) differences in angular momentum loss with respect to solartype stars,and (iii) the small radii of their planets. habitable zones where they arestrongly exposed to the stellar highenergy emission. Our combined K2 missionand Chandra study has shown that previous studies of the Xray rotationconnection are incomplete for slowly rotating and lowactivity fully convectivestars. We aim here at placing the ultimate constraints with ultradeepXMMNewton pointings for three bright, nearby fully convective (M4) stars thathave long rotation periods (30..80 d) derived by us from K2 lightcurves. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]