acis_extract, srclist_filename, /CHECK_POSITIONS, ENERGY_RANGE=[energy
, /SKIP_RECONSTRUCTION, /SKIP_CORRELATION, THETA_RANGE=[value
acis_extract, srclist_filename, /CHECK_POSITIONS, /PLOT
idl tee check_positions_1875.log
acis_extract, 'all.srclist', /CHECK_POSITIONS
acis_extract, 'all.srclist', /CHECK_POSITIONS, /PLOT
- The optional ENERGY_RANGE parameter defines the energy filter used in construction of the multi-ObsId data image; default is [0.5,8.0].
- The optional THETA_RANGE parameter can be used to select a subset of sources for which this stage will be run, based on their off-axis angles.
- The optional keywords /SKIP_RECONSTRUCTION and /SKIP_CORRELATION can be supplied to speed up this stage by skipping the data image reconstructions
and/or skipping the computation of a correlation position estimate.
- The optional keyword MAXLIKELIHOOD_ITERATIONS can be supplied to specify the number of reconstruction iterations; default is 400.
If a vector of integers is supplied (e.g. [10,20,100,500]) then the reconstructed image is saved after each of the specified number of iterations.
For each source the following files are produced:
- a FITS file containing keyword information about the source
- the multi-ObsId (all observations) data image (primary HDU), and reconstructed image (first extension)
- a PostScript atlas containing the raw and reconstructed neighborhood images printed 6 to a page. If you want to preview this atlas you may find that converting to PSF (distill) and viewing with Acroread gives a much better rendering than viewing the PostScript with gv or ghostview.
- a DS9 region file containing a ``point'' region at the position of each event in neighborhood.img
- a DS9 region file containing the source extraction polygons for all the observations, plus markers for the three estimates of the source position (catalog position, correlation peak, and mean of event data).
Several interactive plots show characteristics of the position estimates.
The task of choosing, for each source, which of the available position estimates is best has no simple or obvious solution.
The mean data (RA_DATA, DEC_DATA) and correlation (RA_CORR, DEC_CORR) position estimates can clearly be corrupted by a sloping background caused by the wings of a nearby source.
We strongly suggest in our personal AE recipe (§7.1
) that the observer visually review the position adjustments proposed by AE before adopting them.
Franz Bauer has investigated the various
techniques for calculating source positions, using multiple data sets
for the Chandra Deep Field North, which has good radio and optical
source positions. Based on his work, the PSU ACIS group has decided to
use centroid positions for sources ' off-axis and matched-filter
(correlation) positions for sources ' off-axis.
For some crowded sources the observer may feel that the original position estimate is the most reliable one, and will want to avoid re-positioning those sources.
The observer is encouraged to use the PROVENANCE source property (§7.2) to tag such sources so they can be excluded from re-positioning operations.
7.9.5 PSF and Neighborhood Image Binning
Note that the pixel size used in the multi-ObsId PSF image file and the neighborhood image file will often differ.
The multi-ObsId PSF image is saved at high resolution (by MERGE_OBSERVATIONS), but is re-binned (locally in this stage) to a more appropriate resolution before constructing a matching neighborhood image and performing image reconstruction.
If you wish to manually
run a maximum likelihood reconstruction (outside of AE) then you may need to rebin the PSF to match an existing neighborhood image, as shown by the IDL
You'll need a TARA
release dated April 2007 or later to get the proper version (1.7 or higher) of the tool maxlik.pro
; To test reconstruction set data_name=psf_name
psf_name = 'source.psf'
data_name = 'neighborhood.img'
; Determine the ratio of PSF and data bin sizes.
psf =readfits(psf_name, psf_hdr)
rebin_ratio = sxpar(data_hdr,'CDELT1')/sxpar(psf_hdr,'CDELT1')
; If rebin ratio is not an integer then this approach won't work.
rebin_ratio = round(abs(rebin_ratio))
if (rebin_ratio GT 1) then begin
; Rebin the PSF and save to a temporary file.
print, 'rebinning the PSF'
temp_name = 'temp.fits'
cmd = string(psf_name, rebin_ratio, rebin_ratio, temp_name, F="(%'dmcopy ""%s[bin #1=::%d,#2=::%d]"" %s')")
psf_name = temp_name
; Now we can do reconstructions:
Niter = 200
maxlik, data_name, psf_name, Niter, maxlik_img, maxlik_header, /plot
; The final iteration is returned in the \IDL\ array "maxlik_img".
writefits, 'maxlik200.fits', maxlik_img, maxlik_header
Next: 7.10 SHOW_REGIONS Stage
Up: 7 Using ACIS Extract
Previous: 7.8 MERGE_OBSERVATIONS Stage
Penn State Department of Astronomy