In this chapter we discuss the tasks in xray:xdataio for the input and output of photon lists which are provided as FITS files (with or without a primary array) and which contain one or more extension tables - either ASCII or binary format. The tasks we describe will also access/convert primary and/or secondary images (arrays). (There is also a selection of FITS tools in the ftools package and other input/output tasks in the dataio package of IRAF.)
FITS provides the rules and framework for file structures to TRANSPORT data. Most implementations differ from each other in the selection of optional keywords and in the use of extension tables and images. For this reason, the Einstein Observatory FITS files are different from the US version of ROSAT data, and the MPE ROSAT files come in a third flavor. In order to minimize this disparity, the so called ``Rationalized Data Format" (RDF) was constructed in 1993. Many of the optional choices available have been chosen in the hope that most X-ray missions will adhere to them, thus standardizing X-ray data formats to a greater extent. RDF is used for ROSAT data processed in the US and by MPE commencing April 1994.
To a large extent, the input tasks are designed to recognize differences between FITS flavors for a number of ROSAT processing stages, thus the user does not need to know the particulars of the data formatting. With the implementation of RDF, many modifications to the internal file structure of qpoe files were made. Thus if you have qpoe files on disk generated prior to PROS vs 2.3 (Dec 93 release), you should run upqpoerdf. For more information on RDF files, read the help file explain_xdata. Also, see the Data Products Guide for descriptions of ROSAT files.