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In mid-January 2008, EX Lup, the prototype of the small class of eruptivevariables called EXors, began an extreme outburst that lasted seven months. Weobserved EX Lup during about 21 h with XMM-Newton, simultaneously in X-rays andUV, on August 10-11, 2008 -- a few days before the end of its 2008 outburst --when the optical flux of EX Lup remained about 4 times above its pre-outburstlevel. The observed spectrum of the low-level period is dominated below ~1.5keV by emission from a relatively cool plasma (~4.7 MK) that is lightlyabsorbed (NH~3.6E20 cm^-2) and above ~1.5 keV by emission from a plasma that is~ten times hotter and affected by a photoelectric absorption that is 75 timeslarger. During the X-ray flare, the emission measure and the intrinsic X-rayluminosity of this absorbed plasma component is five times higher than duringthe low-level period. The soft X-ray spectral component is most likelyassociated with accretion shocks, as opposed to jet activity, given the absenceof forbidden emission lines of low-excitation species (e.g., [O I]) in opticalspectra of EX Lup obtained during outburst. The hard X-ray spectral component,meanwhile, is most likely associated with a smothered stellar corona. The UVemission is reminiscent of accretion events, such as those already observedwith the Optical/UV Monitor from other accreting pre-main sequence stars, andis evidently dominated by emission from accretion hot spots. The largephotoelectric absorption of the active stellar corona is most likely due tohigh-density gas above the corona in accretion funnel flows (abridged).

A few days before the end of the 2008 extreme outburst of EX Lup : accretion shocks and a smothered stellar corona unveiled by XMM-Newton