Tips on using SAS and CIAO on the same data

Introduction

Both the Chandra X-ray Observatory's CIAO data analysis package and XMM-Newton's SAS software have some extremely useful functionality not found in the other dataset. Using the other analysis package on data created with one software package most often works as expected, but there are some occasions where problems (either obvious or subtle) appear.

This is an unofficial, selective and incomplete list of bugs and solution. They are randomly ordered.

• Converting XMM fits source lists into ds9-format ascii region files. (watch-out)
• CIAO DM and XMM SAS coordinate keyword differences (tip).
• Filtering XMM images with dmcopy (tip).

Converting XMM fits source lists into ds9-format ascii region files. (SAS 6.5 and Ciao v3.2: minor watch-out)

Description: The SAS task slconv can convert a fits-format source list file produced by XMM tasks eboxdetect or emldetect into a ascii region file of the format produced by ds9, with a complex set of options to control region type, size, labelling, selection and sorting. But there are some things to watch for:

• slconv truncates region sizes to be an exact integer, so for example a circular region of 1.45" would be rounded to 1", which might be a problem in some instances.
• The output region size is hardwired to be quoted as being in arcseconds, so if you want exact sizes based on the known off-axis PSF size or the fitted source extents (which are in pixels) make sure you know the pixel size of the image. slconv does not know this information yourself.
• Some sub-versions of ds9 v4 (I'm not sure which exact sub-version as yet) are confused by the ds9 v3.0 format output by slconv.
• Labeling creates an additional "text" format region, rather than attaching the label to actual region (e.g. as 'fk5;circle(295.14,-58.65,6") # color=green text={source 1}').

Work-arounds: Be careful with your radius expression! Make sure you know the pixel of your image. Avoid the labeling options, i.e. use withlabels=no on the slconv command line.

CIAO DM and XMM SAS coordinate keyword differences (SAS 6.5 and Ciao v3.2: tip)

This useful Ciao Helpdesk entry discusses the differences the differences between Ciao and SAS image coordinate keywords.

Applying ds9 region filters to XMM images with dmcopy (SAS 6.5 and Ciao v3.2: tip)

Description: (to be written)

Solution:

Document history

• 17.11.06 dks: Started documenting some of these issues.