  We present NKBB, an XSPEC model for the thermal spectrum of thin accretion
disks in parametric black hole spacetimes. We employ the Novikov-Thorne model
for the description of the accretion disk and the formalism of the transfer
function proposed by Cunningham for storing all the relativistic effects of the
spacetime metric. The current version of the model assumes the Johannsen
metric, but it can be easily extended to any stationary, axisymmetric, and
asymptotically-flat spacetime without pathological properties. The model can be
used within the XSPEC package to test the Kerr nature of astrophysical black
holes with the continuum-fitting method.
