  We present the results of a five-day monitoring campaign with XMM-Newton of
six X-ray bright young stellar objects (YSOs) in the star-forming complex L1551
in Taurus. All stars present significant variability on the five-day time
scale. Modulation of the light curve on time scales comparable with the star's
rotational period appeared to be present in the case of one weak-lined T Tauri
star. Significant spectral variations between the 2000 and the 2004
observations were detected in the (unresolved) classical T Tauri binary system
XZ Tau: a hot plasma component which was present in the X-ray spectrum in 2000
had significantly weakened in 2004. As XZ Tau N was undergoing a strong optical
outburst in 2000, which had terminated since then, we speculate on the possible
relationship between episodic, burst accretion, and X-ray heating. The
transition object HL Tau underwent a strong flare with a complex temperature
evolution, which is indicative of an event confined within a very large
magnetic structure (few stellar radii), similar to the ones found in YSOs in
the Orion Nebula Cluster.
