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We report initial results from a quasi-simultaneous X-ray/optical observingcampaign targeting V4046 Sgr, a close, synchronous-rotating classical T Tauristar (CTTS) binary in which both components are actively accreting. V4046 Sgris a strong X-ray source, with the X-rays mainly arising from high-density (n_e~ 10^(11-12) cm^(-3)) plasma at temperatures of 3-4 MK. Our multiwavelengthcampaign aims to simultaneously constrain the properties of this X-ray emittingplasma, the large scale magnetic field, and the accretion geometry. In thispaper, we present key results obtained via time-resolved X-ray grating spectra,gathered in a 360 ks XMM-Newton observation that covered 2.2 system rotations.We find that the emission lines produced by this high-density plasma displayperiodic flux variations with a measured period, 1.22+/-0.01 d, that isprecisely half that of the binary star system (2.42 d). The observed rotationalmodulation can be explained assuming that the high-density plasma occupiessmall portions of the stellar surfaces, corotating with the stars, and that thehigh-density plasma is not azimuthally symmetrically distributed with respectto the rotational axis of each star. These results strongly support models inwhich high-density, X-ray-emitting CTTS plasma is material heated in accretionshocks, located at the base of accretion flows tied to the system by magneticfield lines.

The close T Tauri binary system V4046 Sgr: Rotationally modulated X-ray emission from accretion shocks