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

¹ INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy e-mail: francio@astropa.unipa.it
² Dipartimento di Scienze Fisiche ed Astronomiche, Università di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
³ Paul Scherrer Institute, Würenlingen and Villigen, 5232 Villigen PSI, Switzerland
⁴ Columbia Astrophysics Laboratory, Mail Code 5247, 550 West 120th Street, New York, NY 10027, USA
⁵ INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy

Received: 10 October 2006
Accepted: 12 November 2006

Abstract

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 ~5–10 MK and ~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 ~10³¹ erg s^-1. Loop sizes inferred from flare analysis are generally smaller than or comparable to the stellar radius.