  According to the covariant open superstring description of 1/2-BPS D-branes
in the AdS$_5\times$S$^5$ background, there are two kinds of purely instantonic
D-branes. One is the well known D(-1)-brane or D-instanton, and another is the
D1-brane spanning a two dimensional subspace inside S$^5$. We identify the
actual 1/2-BPS instantonic D1-brane configurations and their supersymmetry
structures. From the results, it is concluded that any spherical D1-instanton
with the radius equal to that of S$^5$ is 1/2-BPS. After evaluating the 1/2-BPS
D1-instanton action, we discuss the relation of D1-instanton with the $(p, q)$
string instanton. We also discuss the possible 1/2-BPS and 1/4-BPS multiple
D1-instanton configurations.

High Energy Physics - Theory