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Last modified: March 2018

AHELP for CIAO 4.10


Context: tools


Create a region that shows the location of the HRMA PSF asymmetry for a source


make_psf_asymmetry_region  infile outfile x y [format] [display]
[verbose] [clobber]



Please check the PSF artifact page for the latest information on this feature.

As part of the CXC efforts to push the spatial resolution of Chandra to the sub-ACIS-pixel regime, we have identified a feature in the Chandra/HRC point spread function within the central arcsecond which may affect high fidelity deconvolutions. There is evidence that the feature is also present in Chandra/ACIS data. The problem does not affect images on scales larger than one arcsecond.

This tool creates a region file that highlights the location of this artifact for a source.


Example 1

unix% make_psf_asymmetry_region hrc.fits artifact.reg 16277.518

A region file called artifact.reg will be created that highlights the location of the PSF asymmetry for a source located at the sky coordinates of (16278.23,16415.09). The input file (hrc.fits) is used to determine the roll of the observation (the ROLL_PNT or ROLL_NOM keyword) and the detector scale (the DETNAM keyword).

The region file is in CIAO format (see "ahelp dmregions") and can be displayed in ds9 (see the next example for an example) or used to filter the input file: e.g.

unix% cat artifact.reg
unix% dmcopy "hrc.fits[sky=region(artifact.reg)]" filt.fits

Example 2

unix% make_psf_asymmetry_region hrc.fits artifact.reg 16278.23 16415.09

Setting the display parameter to yes causes ds9 to be launched, showing the contents of the output region file (artifact.reg) displayed on top of the data (hrc.fits).

This can also be achieved by saying:

unix% ds9 hrc.fits -region format ciao -region artifact.reg \
-pan to 16278.23 16415.09 physical -zoom 4

Example 3

unix% make_psf_asymmetry_region acis.fits artifact.reg 4083.21 4093.88

Here we create a region file for an ACIS observation and use the DS9, rather than CIAO, format for the output, which produces a file that looks like:

unix% cat artifact.reg
# Region file fomat: DS9 version 4.1


name type ftype def min max reqd
infile file input       yes
outfile file output       yes
x float     0.5 65535.5 yes
y float     0.5 65535.5 yes
format string   ciao ciao|ds9    
display boolean   no      
verbose integer   1 0 5  
clobber boolean   no      

Detailed Parameter Descriptions

Parameter=infile (file required filetype=input)

Input dataset

This file is used to determine the observation roll (the ROLL_PNT or ROLL_NOM keyword) and the plate scale - the width of a sky pixel in arcseconds - using the DETNAM keyword. It can be any file which contains these two keywords but it is suggested you use an image or event file (otherwise the display option will not work).

Parameter=outfile (file required filetype=output)

Output region file name

The name of the region file created by the tool. The format of the file is controlled by the format parameter.

Parameter=x (float required default= min=0.5 max=65535.5)

X coordinate of source (SKY)

The x coordinate of the source, in sky coordinates.

Parameter=y (float required default= min=0.5 max=65535.5)

Y coordinate of source (SKY)

The y coordinate of the source, in sky coordinates.

Parameter=format (string default=ciao min=ciao|ds9)

Format for output region file

The region file can be written in CIAO format, as a PIE region, or in ds9 format, as a PANDA shape.

Parameter=display (boolean default=no)

Dsiplay infile with region in ds9?

If set, the tool will start a copy of ds9 and display the contents of infile, zoom in on the source and overlay the region showing the PSF asymmetry.

Parameter=verbose (integer default=1 min=0 max=5)

Screen verbosity

At a verbose level of 0 the tool will create no screen output (other than prompting for any required parameters). The default level of 1 displays messages to indicate that the region file has been created and ds9 started (if the display parameter is set). Higher values are used for debugging.

Parameter=clobber (boolean default=no)

Clobber existing file?

If outfile already exists then it will not be overwritten unless the clobber parameter is set.

Changes in the scripts 4.10.1 (April 2018) release

Roll values

The roll is now taken from the ROLL_PNT keyword if it exists, otherwise ROLL_NOM is used. Previously ROLL_NOM was always used. This only makes a difference for data that has been corrected for astrometry shifts or reprojected, and for the small number of multi-obi observations.

HRC radii

The plate scale is now taken from the pixlib module rather than hardcoded, which has resulted in a ~0.05% decrease in the radii in the region files for HRC data.

Changes in the scripts 4.8.1 (December 2015) release

The code has been updated to avoid warning messages from NumPy version 1.9. There is no difference to how the script behaves.

Changes in the December 2011 Release

The script has been updated to run in CIAO 4.4.

About Contributed Software

This script is not an official part of the CIAO release but is made available as "contributed" software via the CIAO scripts page. Please see the installation instructions page for help on installing the package.


See the PSF artifact page for more information on this tool, including any bugs and caveats.

Refer to the CIAO bug pages for an up-to-date listing of known issues.

See Also

aconvolve, acrosscorr, arestore, arfcorr, dmcoords, dmfilth, dmregrid, install_marx, psf_project_ray, psfsize_srcs, simulate_psf, src_psffrac

Last modified: March 2018
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