XSPEC and Response Modeling Keith Arnaud Center for Research Excellence in Space Science and Technology University of Maryland College Park and NASA’s Goddard Space Flight Center

XSPEC has the capacity to use models which apply to the instrumental response. rmodel and rnewpar are the instrumental analogs for the source models applied using model and newpar. Calibration uncertainties which can be defined in terms of a parametrized model can then be included in the fitting. Response model parameters can be given Bayesian priors reflecting the current calibration knowledge.

XSPEC source models have been very successfully because there is a single uniform interface which all must follow. We need the equivalent for instrumental response models. The simplest is: myModel(const RealArray& parameters, const int spectrum, ARF& arf, RMF& rmf) where parameters are the model parameters, spectrum the spectrum number of the response, arf and rmf the vector and matrix parts of the spectral response which might be altered in the function. The ARF and RMF classes would be similar to those defined at http://heasarc.gsfc.nasa.gov/docs/software/lheasoft/headas/heasp/node18.html

Are there any models for calibration uncertainties which could not be handled by such an interface? Is there anything else which should be included in the function input or output?