  Flux calibration of spectra in reverberation mapping (RM) is most often
performed by assuming the flux constancy of some specified narrow emission
lines, which stem from an extended region that is sometimes partially spatially
resolved, in contrast to the point-like broad-line region and the central
continuum source. The inhomogeneous aperture geometries used among different
observation sets in a joint monitoring campaign introduce systematic deviations
to the fluxes of broad lines and central continuum, and intercalibration over
these data sets is required. As an improvement to the previous empirical
correction performed by comparing the (nearly) contemporaneous observation
points, we describe a feasible Bayesian method that obviates the need for
(nearly) contemporaneous observations, naturally incorporates physical models
of flux variations, and fully takes into account the measurement errors. In
particular, it fits all the data sets simultaneously regardless of samplings
and makes use of all of the information in the data sets. A Markov Chain Monte
Carlo implementation is employed to recover the parameters and uncertainties
for intercalibration. Application to the RM data sets of NGC 5548 with joint
monitoring shows the high fidelity of our method.
