  Following hep-th/0305177, we write the boundary state of half S-brane in
bosonic string theory as a grand canonical partition function of a unitary
matrix model. From this representation, it follows that the annulus amplitude
can be written as a grand canonical partition function of a unitary two-matrix
model. We also show that the contribution of the exponentially growing
couplings to the timelike oscillators can be resummed in a certain annulus
amplitude.
