3.3 Basic Extraction

With the various data products required by CIAO located in an observation directory as described above, and with sources created and listed in the source list all.srclist, a basic extraction of the sources from one observation can be accomplished with the following IDL commands (executed from the point_sources run directory):

    obsname  = '1875'
    ; Create extraction regions.
    ae_make_catalog       , obsname, EVTFILE='spectral.evt',PIPELINE_RANDOMIZATION=0
    
    ; Extract spectra and backgrounds.
    ae_standard_extraction, obsname, EVTFILE='spectral.evt'

    ; Repeat the following two commands as needed to improve the size of the background region for each source.
    ae_adjust_backscal_range, MIN_NUM_CTS=100

    ae_standard_extraction, obsname, EVTFILE='spectral.evt', SRCLIST_FILENAME='rerun.srclist', $
                            EXTRACT_SPECTRA=0, TIMING=0, /REUSE_MASKING

    ; Perform photometry, and prepare spectra for fitting.
    acis_extract, 'all.srclist', /MERGE_OBSERVATIONS

• The ae_make_catalog tool (§7.2.2) builds non-overlapping extraction regions for the sources. Those regions are nominally sized to enclose 90% of the local PSF (§5.9), but are iteratively reduced to avoid overlapping extractions in crowded areas. The parameter PIPELINE_RANDOMIZATION is explained in §7.6.

• The tool ae_standard_extraction runs the EXTRACT_SPECTRA (§7.9), EXTRACT_BACKGROUNDS (§7.13), and TIMING (§7.11) stages of AE.

• The call to the ae_adjust_backscal_range tool and repeated call to ae_standard_extraction improve the size of the background region, as described in §7.15.

• The MERGE_OBSERVATIONS Stage is described in §7.16.

Potentially valuable diagnostic plots are available from all these AE stages, as described in §7. For simplicity in this Getting Started tutorial, we omit the plots. We recommend that you visually review the extraction regions (polygons) which are shown in a ds9 session spawned by ae_make_catalog. We also recommend that you visually review the background event list and exposure map formed by masking the point sources which are shown in a ds9 session spawned by ae_standard_extraction.

We recommend that you consider any warning or error messages produced by CIAO or AE; use egrep to scan for them in the log:

  egrep -i "WARNING|ERROR" AE_simple_run.log | egrep -v "error=|No HDUNAME"

Many data products (discussed in other sections) are produced for each source, including source and background spectra, RMF and ARF files, ready for spectral fitting.