  X-ray luminosities of accreting T Tauri stars are observed to be
systematically lower than those of non-accretors. There is as yet no widely
accepted physical explanation for this effect, though it has been suggested
that accretion somehow suppresses, disrupts or obscures coronal X-ray activity.
Here, we suggest that the opposite might be the case: coronal X-rays modulate
the accretion flow. We re-examine the X-ray luminosities of T Tauri stars in
the Orion Nebula Cluster and find that not only are accreting stars
systematically fainter, but that there is a correlation between mass accretion
rate and stellar X-ray luminosity. We use the X-ray heated accretion disk
models of Ercolano et al. to show that protoplanetary disk photoevaporative
mass loss rates are strongly dependent on stellar X-ray luminosity and
sufficiently high to be competitive with accretion rates. X-ray disk heating
appears to offer a viable mechanism for modulating the gas accretion flow and
could be at least partially responsible for the observed correlation between
accretion rates and X-ray luminosities of T Tauri stars.
