  For an extension of the previous work on gravitational lensing by massless
braneworld black holes, we investigate their microlensing phenomena and shadows
and discuss how to distinguish them from standard Schwarzschild black holes and
Ellis wormholes. Microlensing is known as the phenomenon in which luminosity
amplification appears when a bright object passes behind a black hole or
another massive object. We find that, for the braneworld black hole as well as
for the Ellis wormhole, there appears luminosity reduction just before and
after the amplification. This means that observation of such a reduction would
indicate the lens object is either a braneworld black hole or a wormhole,
though it is difficult to distinguish one from the other by microlensing
solely. Therefore, we next analyze the optical images, or shadows of the
braneworld black hole surrounded by optically thin dust, and compare them to
those of the Ellis wormhole. Because the spacetime around the braneworld black
hole possesses unstable circular orbits of photons, a bright ring appears in
the image, just as in Schwarzschild spacetime or in the wormhole spacetime.
This indicates that the appearance of a bright ring does not solely confirm a
braneworld black hole, a Schwarzschild, nor an Ellis wormhole. However, we find
that only for the wormhole is the intensity inside the ring larger than that
the outsider intensity. Therefore, with future high-resolution observations of
microlensing and shadows together, we could identify the braneworld black holes
if they exist.
