  It is noted that X-ray tails (XRTs) of short, hard $\gamma$-ray bursts (SHBs)
are similar to X-ray flashes (XRFs). We suggest a universal central engine
hypothesis, as a way of accounting for this curiosity, in which SHBs differ
from long $\gamma$-ray bursts (GRBs) in prompt emission because of the
differences in the host star and attendant differences in the environment they
present to the compact central engine (as opposed to differences in the central
engine itself). Observational constraints and implications are discussed,
especially for confirming putative detections of gravitational waves from
merging compact objects.
