  Let $n$ be a positive integer and let $0 < \alpha < n.$ In this paper, we
continue our study of the integral equation $$ u(x) = \int_{R^{n}}
\frac{u(y)^{(n+\alpha)(n-\alpha)}{|x - y|^{n-\alpha}}dy.$$ We mainly consider
singular solutions in subcritical, critical, and super critical cases, and
obtain qualitative properties, such as radial symmetry, monotonicity, and upper
bounds for the solutions.
