  We study the pricing problem for corporate defaultable bond from the
viewpoint of the investors outside the firm that could not exactly know about
the information of the firm. We consider the problem for pricing of corporate
defaultable bond in the case when the firm value is only declared in some fixed
discrete time and unexpected default intensity is determined by the declared
firm value. Here we provide a partial differential equation model for such a
defaultable bond and give its pricing formula. Our pricing model is derived to
solving problems of partial differential equations with random constants (de-
fault intensity) and terminal values of binary types. Our main method is to use
the solving method of a partial differential equation with a random constant in
every subinterval and to take expectation to remove the random constants.
