  Short gamma-ray bursts may originate from the merger of double neutron stars
(NS) or that of a black hole (BH) and an NS. We propose that the bright X-ray
flare related to the central engine reactivity may hint a BH-NS merger, since
such a merger can provide more fall-back materials and therefore a more massive
accretion disk than the NS-NS merger. Based on the observed 49 short bursts
with Swift/X-ray Telescope follow-up observations, we find that three bursts
have bright X-ray flares, among which three flares from two bursts are probably
related to the central engine reactivity. We argue that these two bursts may
originate from the BH-NS merger rather than the NS-NS merger. Our suggested
link between the central engine-powered bright X-ray flare and the BH-NS merger
event can be checked by the future gravitational wave detections from advanced
LIGO and Virgo.
