We explicitly construct mock modular forms whose shadows are Eisenstein series of
arbitrary integral and half-integral weight, level and character at the cusps
∞ and
0.
As an application, we give an explicit construction of harmonic weak
Maass forms which are Hecke eigenforms and are the preimages of
Θk, for
k∈{3,5,7}, under the shadow
operator, where
Θ
is the classical Jacobi theta function.