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ASP Conference Series, Vol. 145, 1998

Editors: R. Albrecht, R. N. Hook and H. A. Bushouse

**S. Doe, M. Ljungberg, A. Siemiginowska and W. Joye**

AXAF Science Center, MS 81, Smithsonian Astrophysical
Observatory, 60 Garden Street, Cambridge, MA 02138 USA

The AXAF is NASA's ``Advanced X-ray Astrophysics Facility,'' scheduled
for launch on 27 August 1998. The AXAF Science Center Data Systems
will provide the astronomical community with software to reduce and
analyze AXAF data. In particular, our team is working on a fitting and
modeling application suitable for analysis of AXAF data. We have two
main design goals: to provide modeling in up to 4 dimensions, for
functions truly *f*(*E*,*x*,*y*,*t*); and, to package together a wider variety
of optimization algorithms and fit statistics. Meeting these goals
will enable users to take advantage of the quality of AXAF data.

We have taken an object-oriented approach to the design of the fitting application. Figure 2 shows an example; these are the classes associated with the ``Search Parameter Space'' box shown in the previous figure. Since the design for the classes associated with the other two boxes is substantially the same, we show here only the ``Method'' class.

We provide a number of different optimization algorithms (e.g., the simplex method, Powell minimization, grid search, etc.); each of these are contained in their own separate derived class as shown in Figure 2. All of these classes inherit from the base ``Method'' class, which contains information all the derived classes use. This structure has made it particularly easy for us to ``plug-in'' new algorithms as they are requested by our scientists. There is also a class associated with the Method class called the ``MethodParam'' class; this class contains the convergence criteria used by the various optimization algorithms.

Thus, we have three types of base classes to manage--the Method, Model and Statistic classes. (A ``model'' is composed of an arithmetic combination of functions derived from the Model classes; the fit statistics of the Statistic classes are used to compare the data with the ``predicted data'' generated by models.) Figure 3 shows the managers we use to keep track of the algorithms and models currently in use. The Method and Statistic managers need merely to point at the algorithm currently in use; the Model Manager, on the other hand, needs to construct the model by evaluating three model stacks, the source, background, and instrument model stacks, and then combining them appropriately (i.e., the background model is added to the source model, and the result is convolved with an instrument model). The source model alone may be used, if no background or instrument models have been defined.

We have implemented a version of the fitting application which is currently undergoing alpha testing at the ASC. This version has capabilities which include the following:

- Command-line interface
--Command completion, history, vi, emacs keymaps, escape to shell.

--Execute scripts, create logs.

- Multiple data sets
--E.g., fit data from different missions to the same model.

- Modeling in 1 and 2 dimensions
- Filtering of data in memory
- Modeling ``mini-language''
--Build model out of arithmetic combination of functions.

- Interaction with SAOtng, GNUPLOT, SM
- Selected XSPEC compatibility
- Dynamic linking to user algorithms

This version will serve as the foundation of the flight version.

The first release of ASC software is scheduled for June 1998. For the June release, we must add the following capabilities to the fitting application:

- Implementation of ``joint-mode'' analysis
- Modeling in up to 4 dimensions for functions truly
*f*(*E*,*x*,*y*,*t*) - Additional algorithms and statistical approaches
- Interface with ASC Data Model
- Support for X-ray gratings on AXAF
- Support for external AXAF simulators
- GUI

Adding this functionality to the fitting application will provide AXAF users with a powerful tool for the analysis of AXAF data.

This project is supported by NASA contract NAS8-39073 (ASC). We would like to thank Mark Birkinshaw for making his OPTIM library available at the ASC.

Birkinshaw, M., 1995, CfA internal memo

Doe, S., Conroy, M., & McDowell, J., 1996, in Astronomical Data Analysis Software and Systems V, ASP Conf. Ser., Vol. 101, eds. G. H. Jacoby and J. Barnes (San Francisco, ASP), 155

Doe, S., Siemiginowska, A., Joye, W., & McDowell, J., 1997, in Astronomical Data Analysis Software and Systems VI, ASP Conf. Ser., Vol. 125, eds. Gareth Hunt and H. E. Payne (San Francisco, ASP), 492

© Copyright 1998 Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, California 94112, USA

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