Torsors under some group schemes of order $p\sp n$

Let R be a complete dvr with perfect residue field k of characteristic p>0. Let be the class of R-affine, commutative, smooth of relative dimension one group schemes generically isomorphic to Gm. Let be the class of finite flat commutative group schemes of order pn defined as kernels of the isogenies . We provide an explicit description of torsors over R-schemes under the group schemes and Gλ,n