Some moduli spaces for rank 2 reflexive sheaves on $ {{\mathbf{P}}^3}$

In [Ma], Maruyama proved that the set $ M({c_1},{c_2},{c_3})$ of isomorphism classes of rank $ 2$ stable reflexive sheaves on $ {{\mathbf{P}}^3}$ with Chern classes $ ({c_1},{c_2},{c_3})$ has a natural structure as an algebraic scheme. Until now, there are no general results about these schemes concerning dimension, irreducibility, rationality, etc. and only in a few cases a precise description of them is known. This paper is devoted to the following cases: (i) $ M( - 1,{c_2},c_2^2 - 2r{c_2} + 2r(r + 1))$ with $ {c_2} \geqslant 4$, $ 1 \leqslant r \leqslant ( - 1 + \sqrt {4{c_2} - 7} )/2$; and (ii) $ M( - 1,{c_2},c_2^2 - 2(r - 1){c_2})$ with $ {c_2} \geqslant 8$, $ 2 \leqslant r \leqslant ( - 1 + \sqrt {4{c_2} - 7} )/2$