  To probe the magnetic activity levels of asymptotic giant branch (AGB) stars,
we used XMM-Newton to search for X-ray emission from two well-studied objects,
TX Cam and T Cas. The former star displays polarized maser emission indicating
magnetic field strengths of B ~ 5 G; the latter is one of the nearest known AGB
stars. Neither star was detected by XMM-Newton. We use the upper limits on EPIC
(CCD detector) count rates to constrain the X-ray luminosities of these stars,
and derive L_X < 10^{31} erg s^{-1} (<10^{30} erg s^{-1}) for an assumed X-ray
emission temperature T_X = 3x10^6 K (10^7 K). These limits represent <~ 10% (<~
1%) of the X-ray luminosity expected under models in which AGB magnetic fields
are global and potentially play an important role in collimating and/or
launching AGB winds. We suggest, instead, that the B field strengths inferred
from maser observations are representative of localized, magnetic clouds.
