  We investigate circumstellar and explosion properties of Type Ibn supernovae
(SNe) by analyzing their bolometric light curves. Bolometric light curves of
Type Ibn SNe generally have a large contrast between peak luminosity and
late-phase luminosity, which is much larger than those of 56Ni-powered SNe.
Thus, most of them are likely powered by the interaction between SN ejecta and
dense circumstellar media. In addition, Type Ibn SNe decline much faster than
Type IIn SNe, and this indicates that the interaction in Type Ibn SNe ceases
earlier than in Type IIn SNe. Thus, we argue that Type Ibn SN progenitors
experience high mass-loss rates in a short period just before explosion, while
Type IIn SN progenitors have high mass-loss rates sustained for a long time.
Furthermore, we show that rise time and peak luminosity of Type Ibn and Type
IIn SNe are similar and thus, they have similar explosion properties and
circumstellar density. The similar circumstellar density in the two kinds of
SNe may indicate that mass-loss rates of Type Ibn SN progenitors are generally
higher than those of Type IIn as the wind velocities inferred from narrow
spectral components are generally higher in Type Ibn SNe. We also show that
56Ni mass and explosion energy of Type Ibn SNe may be smaller than those of
other stripped-envelope SNe, probably because they tend to suffer large
fallback or some of them may not even be terminal stellar explosions.
