> aststart
If you are using a version of ASTERIX earlier than 2.3-0 you will need to convert your FITS data into HDS files using the command:
> xrtconv
Begin by getting a summary of the observation with the command showxrt.
ROSAT data is in the form of event tables, that is a logical record containing detection attributes such as position, time, etc. Most analysis cannot make use of the data in this form, but requires uniformly binned data. The ASTERIX command to bin data is xrtsort. With this you can make images, spectra, light curves, etc. It's probably best to make an image first. From this you can select regions for further study using Isys.
Isys or the command driven image processing can be used to inspect the image. Specific regions can then be resorted either by entering simple parameters into xrtsort, such as positions and radii of circles or annuli, or a regional description can be exported from Isys in ARD format (Askii Region Description) then entered into xrtsort. Subsequently the background can be extracted with xrtsub, calibrations and corrections applied with xtrcorr, and an energy response applied with xrtresp. ASTERIX spectral fitting can then be used directly, if you have it installed, or the command ast2xsp can be used to format the data to a form suitable for xspec.
More detailed guidance on data analysis techniques appears in subsequent sections of this guide.