  Motivated by the recent work of Robinson and Wilczek, we evaluate the
gravitational anomaly of a chiral scalar field in a Vaidya spacetime of
arbitrary mass function, and thus the outgoing flux from the time-dependent
horizon in that spacetime. We show that this flux differs from that of a
perfect blackbody at a fixed temperature. When this flux is taken into account,
general covariance in that spacetime is restored. We also generalize their
results to the most general static, and spherically symmetric spacetime.
