RX ROSAT/ASCA data analysis system

updated: 1/5/2000


The major software packages available for examining and analyzing ROSAT and ASCA data, HEASOFT, IRAF/PROS, and MIDAS/EXSAS, meet the needs of most users. However, all software has limitations, and good observers are often never completely satisfied by the job done by someone else's software. There is no single best way to analyze data. Do we need more integrated packages for analyzing ROSAT data? My inclination was to say no, but I found myself doing just that once ROSAT data tapes began arriving at my door. I have been using IDL for nearly two decades, and so found it convenient to use IDL to examine the data. My needs - to read the data in, plot the images, extract sources, and performing timing and spectral analyses - are similar to those of most users. Eventually I put together series of IDL procedures which form a fairly complete ROSAT and ASCA data examination and analysis package. As the code was written with partial support from ROSAT funding, I have decided to make it available to the community. Of course this software is customized to my peculiar analysis needs, and is no more appropriate to the general user than any other package. What can I offer that IRAF/PROS or EXSAS does not? Mainly, I offer software which runs in the IDL environment. Users of IDL need not be reminded of the power of the languge for data examination and for the display of data, nor do they need be reminded of the ease with which procedures can be modified to suit, or written from scratch. I offer this software both as a reasonably complete package for doing simple examination and analysis of ROSAT data, and as a starting point for more detailed tasks. This code complements the procedures available from the ROSAT IDL library at the HEASARC.


The procedures all use a set of variables stored in common. The data, either from the QPOE (.FITS) file or the images, are read into common variables. In this way the data, once read in, are accessible to all procedures, as well as for interactive use. A main program is used to define the common blocks, so that they will be available interactively, though it is not necessary to do this. A driver can be used to read in the data and populate the common variables. By default, the QPOE file is read in, as are the broad-band image and exposure map (or the HRI image, if appropriate). One can read in more, or less, by setting the appropriate keywords. The events are stored in a structure variable. In general, the user is not prompted for inputs; they are passed via keywords, with defaults pre-assigned. On-line help is available to remind the user what keywords are available. A more detailed LATEX documentation file exists. The system currently runs under IDL version 5.1 on VMS and UNIX systems.


The software includes code to:

  • Read in and display FITS images.

  • Overplot coordinate grids, X-ray sources, SIMBAD identifications, HST GSC entries, or arbitrary coordinates, on the image.

  • Read in the QPOE file.

  • Select photons from the QPOE file by X,Y position on the sky or in the detector, by arrival time, or by PH or PI bin.

  • Merge QPOE files and/or images from different observations.

  • Construct images from selected photons.

  • Extract source and background photons. These are placed into structure variables with the same structure as the full events list.

  • Make pulse height spectra in either 256 bins or the 34 SASS bins. Optionally, a .PHA file readable by XSPEC can be produced.

  • Perform timing analyses on the source counts. One can bin the data and plot light curves, plot the distribution of photon arrival intervals, perform K-S tests, and do FFT period-finding analyses.

  • Undertake source detection, using code based on the CAL EINSTEIN system (under development).

    I am continually adding to the set of procedures as I think of new things to do, and will consider suggestions to augment the package.


    Documentation is available in this postscript file. The procedures can be found in the following gzipped tar files: