  We describe the small-time heat kernel asymptotics of real powers $\Delta^r$,
$r \in (0,1)$ of a non-negative self-adjoint generalized Laplacian $\Delta$
acting on the sections of a hermitian vector bundle $\mathcal E$ over a closed
oriented manifold $M$. First we treat separately the asymptotic on the diagonal
of $M \times M$ and in a compact set away from it. Logarithmic terms appear
only if $n$ is odd and $r$ is rational with even denominator. We prove the
non-triviality of the coefficients appearing in the diagonal asymptotics, and
also the non-locality of some of the coefficients. In the special case $r=1/2$,
we give a simultaneous formula by proving that the heat kernel of
$\Delta^{1/2}$ is a polyhomogeneous conormal section in $\mathcal E \boxtimes
{\mathcal E}^* $ on the standard blow-up space $M_{heat}$ of the diagonal at
time $t=0$ inside $[0,\infty)\times M \times M$.
