The PSF density and the cumulative PSF of all telescope-detector combinations aboard the ROSAT satellite as used by the EXSAS analysis system (and the standard ROSAT data analysis system) are described here. All these distributions, save those for the WFC, are azimuthally averaged parts of the observed PSFs and depend on the energy E of the infalling photons as well as the off-axis angle over the corresponding energy range and the off-axis angle range for each mirror-detector optical unit. The derivation of the survey PSF from the PSF in pointing mode is given. Equally, the broadening of the PSF due to the attitude jitter is modelled and verified by a ROSAT HRI observation of a millisecond pulsar without wobbling.
A lot of work went into ground calibrations and in-flight calibrations carried out by many colleagues at the Max-Planck-Institut für extraterrestrische Physik, Garching, Germany, the Astronomisches Institut of the University of Tübingen, Germany, X-ray Astronomy Group of the Department of Physics and Astronomy, University of Leicester, United Kingdom, the United States ROSAT Science Data Center, Harvard University, Smithonian Center for Astrophysics, Cambridge, MA, and the NASA Goddard Space Flight Center, Greenbelt, MD. All of them have contributed to the present knowledge about the mirrors and detectors aboard of ROSAT which provided the base for the implementation of the PSF related software into the EXSAS analysis system. Here is not the place to ascribe the contributions in more detail to persons or groups. In this respect, the interested reader is referred to the related documents below.
It is a pleasure for the author to thank his colleagues P. Predehl and U. Zimmermann from his institute for painstakingly reading the manuscript and for the many constructive comments. Figures 22 and 23 are courtesies of W. Becker from the same institute. The author would also like to thank Frederic Magnard, Institut d'Astrophysique, Paris, for pointing out to him a small difference between Fig. 4 and the corresponding formula (9) in an earlier version.
The ROSAT project has been supported by the German BMFB, DLR, and the Max-Planck society.
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