  In this paper we construct closed expressions that correspond to the
topological charges of the various 1/2-BPS states of the maximal 10 and
11-dimensional supergravity theories. These expressions are related to the
structure of the SUSY algebras in curved spacetimes. We mainly focus on IIB
SUGRA and 11-dimensional SUGRA in a double M9-brane background, with an
emphasis on the SL(2,R) multiplet structure of the charges and how these map
between theories. This includes the charges corresponding to the multiplets of
7- and 9-branes in IIB. We find that examining the possible multiplet
structures of the charges provides another tool for exploring the spectrum of
BPS states that appear in these theories. As a prerequisite to constructing the
charges we determine the field equations and multiplet structure of the
11-dimensional gauge potentials, extending previous results on the subject. The
massive gauge transformations of the fields are also discussed. We also
demonstrate how these massive gauge transformations are compatible with the
construction of an SL(2,R) covariant kinetic term in the 11-dimensional
Kaluza-Klein monopole worldvolume action.
