M. W. Wise, D. P. Huenemoerder, and J. E. Davis
MIT/ASC
The AXAF Science Center Data System will include the ability to simulate the detailed response of the AXAF to X-ray sources. These simulations will be used for a variety of purposes including: development of processing algorithms; ground-based and on-orbit performance prediction; testing of the standard processing pipelines; and scientific observation planning and prediction. As part of this modelling effort, the AXAF Science Center group at MIT has developed a modular, portable, stand-alone simulator MARX (Model of AXAF Response to X-rays). MARX includes models of the AXAF mirrors, the low- and high-energy transmission grating assemblies (LETG and HETG), and the HRC and ACIS focal plane detectors. The modular design allows the user to choose among several modes of operation, such as either a ray-trace of the AXAF mirrors or a model of the mirrors based on data obtained from external performance models. A number of simple source models (extended or point-like) are supported and users may extend the capabilities by incorporating their own models. Sources may have arbitrary spectral energy distributions. Output is in the form of a photon event list from which images and spectra may be extracted. The simulator is reasonably compact (requiring only 6 MBytes for the entire distribution) and fast (3000 photons/sec on a SPARC 20). It is written in C and has been successfully compiled under SunOS, Solaris, and Linux. The simulator was originally developed to provide sample AXAF data with an exactly known instrument response in order to develop and test spectral extraction and analysis algorithms. It has also become a useful tool for scientific observation planning. To demonstrate its capabilities, we present simulated AXAF images and spectra for several cosmic sources including: stellar coronae; the central regions of nearby galaxies; cluster cooling flows; high redshift clusters; and active galactic nuclei. We will also show sample performance predictions for the ground calibration sources at the AXAF X-ray calibration facility. Although developed initially for internal use, the AXAF Science Center does plan to make MARX available to the community as a tool for proposal planning.