Chandra X-Ray Observatory
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Last modified: 13 September 2017

URL: http://cxc.harvard.edu/ciao/PSFs/chart2/runchart.html

Run ChaRT

Introducing ChaRT v2

Several changes to the options and inputs required to run ChaRT have been introduced in the latest version—allowing for simulations compatible with sub-pixel analysis, in particular—including input source spectrum format or inclusion of observation-specific aspect solution files. Details are described in the Preparing to Run ChaRT thread.

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.


User Information
Email Address
Source Coordinates
Celestial:
R.A.
Dec.
Off Axis Angle:
θ [arcmin],
ϕ [deg]
Source Spectrum
Spectrum file:
Monochromatic Energy: [keV],
Photon Flux: [photons/cm^2/sec]
Pointing Information
Observation:
OBS_ID
OBI_NUM
Upload aspect solution file:
Other, specify:
R.A.:
Dec.:
Roll:
Exposure: [ksec]
Realizations
Number of iterations
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.

Coordinates

Chart is used to simulate a point source PSF at a specific location. The user can choose to enter coordinates in either Celestial or Chandra Detector coordinates.

R.A.

The right ascension of the source position. The value may be supplied in decimal degrees or in sexagesimal format. Values are required to be J2000.

Dec

The declination of the source position. The value may be supplied in decimal degrees or in sexagesimal format. Values are required to be J2000.

Off-axis Angle

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

Azimuthal Angle

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

Source Spectrum

The spectrum of the source can be supplied as either a single monochromatic energy or by uploading a file containing the source spectrum.

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 spectrum file must contain 3, and only 3 columns in the following order: lower energy limit (keV), upper energy limit (keV), and photon flux photon/cm2/sec. Both FITS and various ASCII formats are supported.

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

Monochromatic Energy

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

Photon Flux

The photon flux, photon/cm2/sec, at the specified monochromatic energy. The value should be between 1.0e-9 and 1.0e-2 photon/cm2/sec.

Pointing Information

Users need to supply information about the Chandra pointing. Most Chandra observations are taken while the spacecraft pointing dithers around some nominal location. This has a blurring effect on the PSF as discussed in the Preparing to Run ChaRT thread.

The pointing information is supplied via the aspect solution file or by supplying a single pointing.

OBS_ID

The OBS_ID of the observation being analyzed. The aspect solution file can be retrieved from the Chandra archived automatically; saving the user from having to upload the file.

Be sure to double check the list of reasons why users not use this option in the Preparing to Run ChaRT thread.

OBI_NUM

There are a very small number of multi-obi observations: observations separated in time that share the same OBS_ID value. These observations need to be processed separately; the OBI_NUM value in the header is used to distinguish them.

This box will be disabled unless the user enters the a value for one of the mutli-obi observations into OBS_ID field.

Upload aspect solution file

Users analyzing proprietary dataset or who have made modifications to the aspect solution file must upload the aspect solution file to ChaRT.

R.A.

The right ascension of the telescope pointing. The value may be supplied in decimal degrees or in sexagesimal format. Values are required to be J2000.

Users doing analysis with Chandra detector coordinates can set this value to 0.

Dec.

The declination of the telescope pointing. The value may be supplied in decimal degrees or in sexagesimal format. Values are required to be J2000.

Users doing analysis with Chandra detector coordinates can set this value to 0.

Roll

The roll angle of the pointing relative to North. The value must be between 0 and 360 degrees.

Users doing analysis with Chandra detector coordinates can set this value to 0.

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.

Realizations

Multiple simulations using the same parameters may be necessary to obtain sufficient number of counts to overcome the statistical noise. ChaRT allows users to run upto 50 iterations each with a unique random seed.

Number of iterations

The number of simulations to perform. The same source parameters are used for each iterations, each done with a different random seed.

Users may request between 1 and 50 iterations.

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.

The random seed is incremented by 1 for each realization after the first.


Last modified: 13 September 2017
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