  Thermal radiation, peaking in soft X-rays, has now been detected in a handful
of GRB afterglows and has to date been interpreted as shock break-out of the
GRB's progenitor star. We present a search for thermal emission in the early
X-ray afterglows of a sample of Swift bursts selected by their brightness in
X-rays at early times. We identify a clear thermal component in eight GRBs and
track the evolution. We show that at least some of the emission must come from
highly relativistic material since two show an apparent super-luminal expansion
of the thermal component. Furthermore we determine very large luminosities and
high temperatures for many of the components-too high to originate in a SN
shock break-out. Instead we suggest that the component may be modelled as late
photospheric emission from the jet, linking it to the apparently thermal
component observed in the prompt emission of some GRBs at gamma-ray and hard
X-ray energies. By comparing the parameters from the prompt emission and the
early afterglow emission we find that the results are compatible with the
interpretation that we are observing the prompt quasi-thermal emission
component in soft X-rays at a later point in its evolution.
