  X-ray transients appeared in optically non-active galactic nuclei have been
observed in recent years. The most popular model explaining this kind of
phenomena is the conventional tidal disruption model. In this model, when a
star moves within the tidal radius of a black hole, part of the star materials
will fall into the black hole through an accretion disk, which gives rise to
the luminous flare. We propose that the X-ray emission may not necessarily come
from radiation of the accretion disk alone. Instead, it may be related to a
jet. As the jet travels in the interstellar medium, a shock is produced and
synchrotron radiation is expected. We compared the model light curve and the
synchrotron radiation spectrum with the observed data, and find that our model
explains the observed light curve and late-time spectrum well. Our model
predicts that these transient active galactic nuclei could be sources of the
future gamma-ray satellites, e.g. GLAST and the emission region will be
expanding with time.
