Chandra X-Ray Observatory
	(CXC)
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Last modified: 4 March 2014

URL: http://cxc.harvard.edu/chart/runchart.html

Run ChaRT

ChaRT is a web interface to the SAOsac raytrace code which was developed by the CXC for calibration purposes. A raytrace matching the user inputs is run through the Chandra optics to produce a collection of rays. An email is sent to the user when the raytrace data is available for download.

This web interface handles one simulation at a time (i.e. you can't submit multiple sources at once), but users can submit multiple jobs one after another to simulate multiple sources.

For detailed instructions on obtaining ChaRT inputs, follow the Preparing to Run ChaRT thread.


Email address:
Off-axis Angle [arcmin]:
Azimuthal Angle [degree]:

Select the type of simulation:

  • spectrum and exposure time
  • monochromatic energy and ray density
Spectrum File:
Exposure Time [ksec]:
Random Seed:

Explanation of ChaRT inputs

For detailed instructions on obtaining ChaRT inputs, follow the Preparing to Run ChaRT thread.

Email Address

ChaRT sends an email when your job has finished running and the data is available on the FTP site. The CXC may also contact you at this email address if there is a problem running the ChaRT job.

Off-axis Angle

The off-axis angle of the source, theta, in arcminutes.

Azimuthal Angle

The azimuthal angle of the source, phi, in degrees.

Spectrum File

The definition of the spectrum at the entrance aperture of the HRMA for which you would like a PSF to be simulated.

The format is an ASCII file consisting of two columns separated by spaces or tabs. The first column is the energy (in keV) at the center of the bin and the second column is the flux (in photons/cm2/sec) of the bin. All flux values must be non-zero; a zero in the flux column will cause ChaRT to fail.

This file may be created with the save_chart_spectrum function in Sherpa, as shown in the Preparing to Run ChaRT thread.

Exposure Time

The duration of the simulation in ksec. The maximum exposure time is 200 ksec.

This value is usually chosen to match the exposure time of an observation, which is stored in the EXPOSURE header keyword of the event file.

Monochromatic Energy

A single monochromatic energy in keV for the simulation. The allowed energy range is 0.2 - 10 keV.

Ray Density

The density of rays in rays/mm2 that will be generated at the entrance aperture. The number of rays that arrives at the focal plane is determined by the HRMA effective area for the input monochromatic energy. The allowed range is 0.0001 - 10 rays/mm2.

Random Seed

A random seed that allows the ray generator to create a thoroughly random and statistically appropriate sampling of rays. The default value, -1, indicates that the system's clock time will be used.

To recreate a previous run of ChaRT, you must enter the same seed value.


Last modified: 4 March 2014
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