  Classical T Tauri stars (CTTSs) accrete matter from the inner edge of their
surrounding circumstellar disks. The impact of the accretion material on the
stellar atmosphere results in a strong shock, which causes emission from the
X-ray to the near-infrared (NIR) domain. Shock velocities of several 100 km
s$^{-1}$ imply that the immediate post shock plasma emits mainly in X-rays.
Indeed, two X-ray diagnostics, the so-called soft excess and the high densities
observed in He-like triplets, differentiate CTTSs from their non-accreting
siblings. However, accretion shock properties derived from X-ray diagnostics
often contradict established ultraviolet (UV)-NIR accretion tracers and a
physical model simultaneously explaining both, X-ray and UV-NIR accretion
tracers, is not yet available.
  We present new XMM-Newton and Chandra grating observations of the CTTS T
Tauri combined with UV and optical data. During all epochs, the soft excess is
large and the densities derived from the O VII and Ne IX He-like triplets are
compatible with coronal densities. This confirms that the soft X-ray emission
cannot originate in accretion funnels that carry the bulk of the accretion rate
despite T Tauri's large soft excess. Instead, we propose a model of radially
density stratified accretion columns to explain the density diagnostics and the
soft excess. In addition, accretion rate and X-ray luminosity are inversely
correlated in T Tauri over several epochs. Such an anti-correlation has been
observed in samples of stars. Hence the process causing it must be intrinsic to
the accretion process, and we speculate that the stellar magnetic field
configuration on the visibile hemisphere affects both the accretion rate and
the coronal emission, eventually causing the observed anti-correlation.
