  We calculated the bolometric images of relativistic slim disks during
radiation-pressure-driven thermal instability. When the mass-accretion rate
exceeds the critical one, an inner region of the standard accretion disk bursts
to change to a slim disk state having a large scale height. That is, the inner
region of the disk becomes high temperature, and the thickness of the disk
increases due to the increase of the radiation pressure. As a result, we found
that the observed image of the disk during the burst strongly depends on the
inclination angle. That is, radiation from the innermost disk would be occulted
by the disk outer rim for high inclination angles($i \gtrsim 70^\circ$). We
also calculated the spectral energy distribution during thermal instability.
The Wien peak of the spectrum of high inclination angles becomes softer than
that of low inclination angles due to the geometrical thickness. From these
facts, even if the burst happens in black hole candidates, we may not observe
the burst when the inclination angle is large. We may suggest that numerous
luminous black hole candidates are still hidden in our Galaxy.

Astrophysics