ASTERIX ROSAT Tutorials - Initial.csh

The initial.csh script

The following links provide access to a script (and its associated files) - INITIAL.CSH - which reduces ROSAT data, creates images and performs preliminary source searching.

Our intention is that this script will provide an introduction into ROSAT data reduction techniques and illustrate of the flexibility of ASTERIX programs when used in scripts.

These scripts can be downloaded from the browser. They are also available from our FTP site - ftp.sr.bham.ac.uk - in directory /pub/asterix/examples.

If you have any problems locating or running these scripts please contact us.

Download

• Download the script and its associated files :

  Initial script tar.

• View the script :

  View initial script

• View the help :

  Initial help

Note - other files (default.set pkstart extra) which are required are included in the .tar file.

Method

Briefly the script performs the following tasks :

• 1. Unpack data (gunzip,tar,uncompress.)
• 2. Get good time periods. XRTHK
• 3. Sort cube. XRTSORT
• 4. Create background cube with annulus.
• 5. Background subtract data and create background model. XRTSUB
• 6. Project to images and source search. PROJECT PSS
• 7. Recreate background cube this time excluding point sources found in 6).
• 8. Repeat 5), 6), 7) and 8) until same number of sources are found each time.
• 9. Check that background model does appear to give a good description of the data. Warn if it doesn't.
• 10. Final background subtraction. Correct cube (dead time,wires,counts/sec,etc) and attach a spectral response.
• 11. Create final images. Clean up.

Additional points

Note :

• The Background - Defining a background model is and instrument dependant processes. For ROSAT this process is iterative. Because initially there is no background model XRTSUB uses an assumed source free section of the data (an output from XRTSORT or in this case simply a copy of the original dataset) to generate a model. The approximate model created by XRTSUB is used in PSS to identify any faint sources in the assumed source free section. These faint sources are masked out of the source free section and the data again input into XRTSUB and PSS. This continues until no new sources are found.

• Spectral cubes - Rather then work with images the initial.csh script uses spectral cubes of information and projects them to images where images are required. Spectral cubes are larger but they are generally found to be more flexible and a requirement for certain applications.

• Scaling factor - A section of this script (lines @175-240) checks the scaling background factor. This is a useful check but a less important consideration with respect to data reduction.