Spectral properties of X-ray bright variable sources in the Taurus molecular cloud

Aims. We analyze 19 bright variable X-ray sources detected in the XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST), to characterize the variations with time of their coronal properties and to derive information on the X-ray emitting structures. Methods. We performed time-resolved spectroscopy of the EPIC PN and MOS spectra of the XEST sources, using a model with one or two thermal components, and we used the time evolution of the temperatures and emission measures during the decay phase of flares to derive the size of the flaring loops. Results. The light curves of the selected sources show different types of variability: flares, long-lasting decay or rise through the whole observation, and slow modulation or complex flare-like variability. Spectral analysis shows typical quiescent plasma temperatures of similar to 5-10 MK and similar to 15-35 MK; the cool component generally remains constant, while the observed flux changes are due to variations of the hot component. During flares the plasma reaches temperatures up to 100 MK and luminosities up to similar to 10(31) erg s(-1). Loop sizes inferred from flare analysis are generally smaller than or comparable to the stellar radius.