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Last modified: 1 Dec 2006
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Create a PSF

[CIAO 3.4 Science Threads]


Overview

Last Update: 1 Dec 2006 - updated for CIAO 3.4: ChIPS version

Synopsis:

The Chandra Ray Tracer (ChaRT) gives the best available HRMA Point Spread Function (PSF) for a point source at any off-axis angle and for any energy or spectrum. The PSF libraries are used in this thread to create a PSF for a specific observation. A comparison of these methods is available from the ChaRT webpages.

Purpose:

To create an image of the PSF for a source, and normalize it to the source flux. The PSF changes with source position and photon energy, and is created by interpolation of a library of pre-launch calibration files (the PSF hypercube library).

Read this thread if:

you would like to create a PSF for an HRC or ACIS imaging observation.

Related Links:

Proceed to the HTML or hardcopy (PDF: A4 | letter) version of the thread.



Contents


The PSF Libraries

To create a PSF for a source, the PSF library for the instrument of interest (i.e. ACIS or HRC) must be installed. These libraries are supplied as part of the CALDB and can be downloaded if they are not already available. The ACIS and HRC libraries are stored in $CALDB/data/chandra/acis/cpf/2dpsf/ and $CALDB/data/chandra/hrc/cpf/2dpsf/ respectively: 

unix% ls -1 $CALDB/data/chandra/acis/cpf/2dpsf/
README.txt
acisi1998-11-052dpsf1N0002.fits
acisi1998-11-052dpsf2N0002.fits
acisi1998-11-052dpsf3N0002.fits
acisi1998-11-052dpsf4N0002.fits
aciss1998-11-052dpsf1N0002.fits
aciss1998-11-052dpsf2N0002.fits
aciss1998-11-052dpsf3N0002.fits
aciss1998-11-052dpsf4N0002.fits
cxcpsflib.manual.ps@

unix% ls -1 $CALDB/data/chandra/hrc/cpf/2dpsf/
README.txt
cxcpsflib.manual.ps@
hrci1998-11-052dpsf1N0002.fits
hrci1998-11-052dpsf2N0002.fits
hrci1998-11-052dpsf3N0002.fits
hrci1998-11-052dpsf4N0002.fits
hrcs1998-11-052dpsf1N0002.fits
hrcs1998-11-052dpsf2N0002.fits
hrcs1998-11-052dpsf3N0002.fits
hrcs1998-11-052dpsf4N0002.fits

The PSF changes with both the energy of the incoming photons and their location on the focal plane of the instrument, as described in the Chandra Proposers' Observatory Guide. Each library contains a grid of PSF images covering a range of energies and locations on the detector plane; linear interpolation of these images is used to create the requested PSF.

Currently the PSF library is evaluated at five energies - 0.277 keV, 1.4967 KeV, 4.51 keV, 6.4 keV, and 8.6 keV - for a range of positions that depend on which library is used. A summary of the available libraries is available in the PSF Library section of the CIAO dictionary. The recommended libraries are the f1 and f2 files for each detector; use the f1 library if the off-axis angle of the source is within the library's field of view, otherwise use the f2 library (see the PSF library manual (PS, 16pp) for the area covered by each library).


Get Started

Sample ObsID used: 1838 (ACIS-S, G21.5-09)

File types needed: evt2; asol1

In this thread we only use data in the energy range 0.3 to 8 keV; an image of the source region is also created: 

unix% dmcopy "acisf01838N001_evt2.fits[energy=300:8000]" acis_1838_evt2.fits
unix% dmcopy "acis_1838_evt2.fits[bin x=3821:4320:1,y=4000:4499:1]" img_src_0.3-8keV.fits

Characterizing the Source