  GRB 121027A is un-usual with its extremely long-lasting, energetic X-ray
flares. The total energy release in X-ray flares is about one order of
magnitude higher than prompt gamma-rays, making it special from most long GRBs.
We show that while the prompt gamma-ray emission satisfies the empirical
E_{iso}-E_{p} relation of typical long GRBs, the X-ray flares, whose spectra
can be fit with a cutoff-power-law model with well-constrained E_p,
significantly deviate from such a relation. Nonetheless, a time-resolved
spectral analysis of X-ray flares suggest that the X-ray emission is consistent
with the L_{iso}-E_{p} relation of long GRBs. We constrain the minimum Lorentz
factor of the X-ray flares to be ~14, which is consistent with the
Gamma-L_{iso} relation. Our results imply that prompt gamma-ray emission and
late X-ray flares share the similar radiation mechanism, but originate from the
outflows with different Lorentz factors. We search for similar GRBs from the
Swift GRB archives, and find that the z=6.29 GRB 050904 is a carbon copy of GRB
121027A. The long-lasting, energetic X-ray flares in these GRBs demand
significant accretion at late times, which point towards a large-radius
progenitor star.
