  A continuous one-parameter group of unitary isometries of a right Hilbert
C*-bimodule induces a quasi-free dynamics on the Cuntz-Pimsner C*-algebra of
the bimodule and on its Toeplitz extension. The restriction of such a dynamics
to the algebra of coefficients of the bimodule is trivial, and the
corresponding KMS states of the Toeplitz-Cuntz-Pimsner and Cuntz-Pimsner
C*-algebras are characterized in terms of traces on the algebra of
coefficients. This generalizes and sheds light onto various earlier results
about KMS states of the gauge actions on Cuntz algebras, Cuntz-Krieger
algebras, and crossed products by endomorphisms. We also obtain a more general
characterization, in terms of KMS weights, for the case in which the inducing
isometries are not unitary, and accordingly, the restriction of the quasi-free
dynamics to the algebra of coefficients is nontrivial.
