) sources that are extracted on-axis (THETA
') and are uncrowded (PSF_FRAC
) in both ObsIDs.
If a reference catalog (such as 2MASS) has been converted into the format used by our match_xy tool, then the offset between it and each ObsID is also estimated.
EXAMPLE (assuming the standard directory structure (§3):
setenv OBS_LIST ""
foreach dir (../obs*)
if (! -d $dir) continue
set obs=`basename $dir | sed -e "s/obs//"`
setenv OBS_LIST "$OBS_LIST $obs"
end
echo $OBS_LIST
idl
.run ae
; Without a reference catalog
ae_interObsID_astrometry, strtrim(strsplit(getenv('OBS_LIST'), /EXTRACT), 2)
; With a reference catalog
.run match_xy
event2wcs_astr = get_astrometry_from_eventlist('../../tangentplane_reference.evt')
twomass_cat = build_FITS_cat('2mass_highqual.fits', event2wcs_astr, RA_EXPRESSION='tb.RAJ2000', DEC_EXPRESSION='tb.DEJ2000', RA_ERROR_EXPRESSION='(tb.errmaj+tb.errmin)/2', DEC_ERROR_EXPRESSION='(tb.errmaj+tb.errmin)/2', NAME='TWOMASS')
ae_interObsID_astrometry, strtrim(strsplit(getenv('OBS_LIST'), /EXTRACT), 2), ASTROMETRY=event2wcs_astr, REF_CATALOG=twomass_cat
The collated FITS table itself can be searched for a list of LABELs using the tool ae_label2name.
EXAMPLE:
.run ae
ae_label2name, ['101','202','303'], 'all.collated'
ae_label2name, 3, 'all.collated'
The parameter labels can either be a string array, or an integer.
If an integer is supplied, then the tool prompts for you to enter the specified number labels.
Alternatively, such a table can be constructed in ASCII form using the LABEL_FILENAME option to the Collate Stage (§7.12), and then searched for a specific LABEL either manually or with grep. For example, if the Collate Stage has produced the ASCII table label.txt then this shell alias would change directories to the source with the specified label:
alias asl 'setenv LINE `grep -i "(\!:1)" label.txt`; echo $LINE; if ( "$LINE" != "" ) pushd `echo $LINE | cut -c 1-18`;'
EXAMPLE:
; Create an emap at 1 keV named 'fullfield_1' using six CCDs and an emap named 'iarray_1' using only ACIS-I.
.run ae
ae_make_emap, 'acis.evts', ['fullfield_1','iarray_1'], CCD_LIST=['012367','0123'], ARDLIB_FILENAME='./ardlib.par', ASPECT_FN='acis.asol1', PBKFILE='acis.pbk0', MASKFILE='acis.msk1', MONOENERGY=1.0
EXAMPLE:
.run ae
ae_group_spectrum, '182029.89-161044.4.pi', '182029.89-161044.4_bkg.pi', '', SNR_RANGE=[5,10]
EXAMPLE:
.run ae
ae_timerange_extract, '182029.80-161045.5', '6420', '270786808.58:270854668.99', '6420.1', EVTFILE='spectral.evt'
ae_timerange_extract, '182029.80-161045.5', '6420', '270854678.71:270897521.73', '6420.2', EVTFILE='spectral.evt'
ae_timerange_extract, '182029.80-161045.5', '6420', '270897531.45:270938175.77', '6420.3', EVTFILE='spectral.evt'
CIAO provides a tool named srcextent that may be helpful to you. AE provides a very simple tool named ae_radial_profile that can quickly scan every AE source for signs that a source might be inconsistent with the PSF. The tool compares the merged event data with the merged PSF. The basic call is shown below. The 2011mar16 or later version of our TARA package is required.
If you ran AE's MERGE stage with a MERGE_NAME option, then supply that same option above.
The output data structure (``report'' above) is an array of structures Each source reports K-S probabilities quantifying the similarity between the event data and PSF model within a circular aperture defined by SRC_RADIUS, in three ways:
From this report, you can make a list of sources that claim inconsistency with the PSF (low K-S values) using forprint, e.g.
Then, you can run ae_radial_profile a second time on this shorter source list, using the PLOT option to produce three interactive plots for the source showing cumulative distributions of radial distance, X-offset, and Y-offset; press the ``next source'' to move to the next source.
The tool takes an optional ENERGY_RANGE parameter that specifies the event energy band on which you want to compare to the PSF
The default is [0.5,8] keV, which may be too broad for your taste or not appropriate for the PSF energy you have used.
Although the plots look reasonable, I certainly cannot guarantee that there are no mistakes in this tool. In such code it's easy to be off-by-one-pixel in a calculation, or to confuse PSF pixels and sky pixels, or to make any number of other mistakes. For any source that this tool claims is ``extended'', you should try to verify that conclusion by other means.
The ae_radial_profile code is fairly well commented. You should be able to read it without too much difficulty if you want to understand what it is doing.
In October 2010 the Chandra X-ray Center announced the discovery of a hook-shaped feature in the Chandra PSF
that extends 
0.8" from the main peak and contains 5% of the flux. Its location depends upon the roll angle of the observation; given its limited spatial extent, the hook is not discernable for sources observed substantially off-axis. At this time, its energy dependence (either spatially or as a fraction of the total power) is not well-characterized. No revised PSF models incorporating the hook-shaped feature are currently available.
Since this feature is not represented in the available PSF models, image reconstructions may generate spurious candidate point sources near bright sources (e.g. those with 
100 counts obtained with a single roll angle and located 
4' off-axis), where enough counts might be distributed along the hook that it could be reconstructed into what appears to be one or more independent, faint point sources.
Until a model for this feature is available, observers are encouraged to review the regions around all bright sources expected to be significantly contaminated by the hook feature to identify detections that are spatially coincident with the hook feature. Such sources should be considered suspicious, unless they contain substantially more than 5% of the flux of their neighboring bright source.
The tool ae_make_psf_hook_regions will construct a region file marking the hook region (for each ObsID) around sources that have more than a specified number of counts expected in the hook and lie within a specified off-axis angle. For example:
Once a list of suspicious detections is identified, their individual extractions can be examined with the hook regions displayed via the SHOW stage, e.g.
Running ChaRT is not easy, but we've written a tool (ae_chart_interface) that calculates the ChaRT parameters you need, downloads the rays, and processes them into an AE-compatible set of PSF images. The ChaRT PSF is blurred by the same method used in AE (§5.1.2). For example, to create ChaRT PSFs for observation ``4495'' at the location of the source ``104357.47-593251.3'':
.run ae ae_chart_interface, '104357.47-593251.3', '4495'Supply the optional parameter /PIPELINE_RANDOMIZATION, described in §E.1, as appropriate.
Then, cd to the source's observation directory and create a symbolic link that will cause the ChaRT PSFs to be used by AE:
cd 104357.47-593251.3/4495 mv source.psf AE_source.psf ln -s chart_source.psf source.psf.
EXAMPLE:
plot_spectra.pl 18*/nogrp_tbabs_vapec/ldata.ps
This tool is a re-implementation of the Perl tool spectra_viewer.pl developed by Konstantin Getman. The X Windows program gv is used to display the Postscript spectra produced by XSPEC. You must have the GNU implementation of gv (version 3.6.1 or higher) in your Unix path.
EXAMPLE:
.run ae
; Set the default ``best model'' to ``nogrp_tbabs_vapec'' for all sources.
; Use /FORCE keyword to override any existing BEST_MDL values.
ae_default_model_preference, 'all.srclist', 'nogrp_tbabs_vapec'
; Interactively review each source.
ae_spectra_viewer, 'all.srclist', HDUNAME='*'
; Collate the ``best model'' results.
acis_extract, 'all.srclist', COLLATED_FILENAME='best_model.collated', HDUNAME='BEST_MDL'
By careful construction of the source list passed to ae_spectra_viewer the observer can review the sources in whatever order is most convenient, or review only a subset of the catalog. For example you might collate (§7.12) the fit results from a standard model for the whole catalog, and then make a list of the sources with suspicious fit results for interactive review.
EXAMPLE:
.run ae
ae_perform_fit, '181948.82-160624.2', 'nogrp_tbabs_vapec'
<source>/spectral_models/.
The COLLATE stage of AE produces a FITS table with vector columns, in order to record source properties over many energy bands. The tool ae_flatten_collation transforms the AE collation into a more convenient and scientifically useful FITS table.
The tool hmsfr_tables (in acis_extract_tools.pro) converts the FITS table produced by ae_flatten_collation into several LATEX tables of AE results that we find useful in our star formation research. Stubs of these are shown in Figures 1, 2, and 3. Several IDL ``.sav'' files holding various source parameters are also produced. This program has not yet been adequately documented, although the code comments give some information and it is used in our example recipe (§7.1).