Subsections

• E..2.1 Actions
• E..2.2 Usage and Inputs
• E..2.3 Data Products

E..2 EXTRACT_EVENTS Stage

This stage is a subset of the EXTRACT_SPECTRA Stage (§E.3). To save computer time it would be run (instead of running EXTRACT_SPECTRA) in preparation for the optional stage SHOW_REGIONS, as shown in Figure 8.

E..2.1 Actions

• Data from the neighborhood of the source are selected to help visualize the source in the SHOW_REGIONS stage.

• The PSF fraction associated with the source extraction region is computed for all the energies at which a PSF is available. A warning is printed if the source extraction region falls outside the field of view of the PSF images so the observer will know that the PSF fraction is underestimated.

• The observation data is filtered by the source extraction region to produce a source event list.

• The source events are energy filtered and various statistics are computed on the in-band events and saved as FITS keywords in obs.stats including:
  X_DATA, Y_DATA: the mean sky coordinates of the in-band extracted events.
  

  EX_DATA, EY_DATA: 1-sigma error estimates for X_DATA, Y_DATA.¹⁵

• Plots summarizing the results of EXTRACT_EVENTS are presented. These plots are diagnostic tools that help you spot problems in your data, in your catalog, in your CIAO configuration, in the CIAO software, or in the AE software. Some plots may also convey scientifically interesting information about your sources.

The source extraction region ({sourcename}/{obsname}/extract.reg) is of course normally a polygon constructed by the CONSTRUCT_REGIONS stage. Any CIAO-compatible region file may be used however, including ones containing multiple components using the ``+'' and ``-'' CIAO syntax. For example, to extract a source suffering pileup on observer may replace AE's region with an annular region. Whatever region is found in extract.reg is used both to filter the event data and to filter the PSF images to compute a PSF fraction curve.

E..2.2 Usage and Inputs

acis_extract, srclist_filename, obsname, obsdata_filename, /EXTRACT_EVENTS, ENERGY_RANGE=[energy,energy], EMAP_FILENAME=filepath, WARNING_REGION_FILENAME=filepath, NEIGHBORHOOD_SIZE=value, /REUSE_NEIGHBORHOOD

acis_extract, srclist_filename, obsname, /EXTRACT_EVENTS, /PLOT

EXAMPLE:
idl $\vert\&$ tee extract_events_1875.log

acis_extract, 'all.srclist', '1875', '../obs1875/spectral.evt', /EXTRACT_EVENTS, ENERGY_RANGE=[0.5,8], EMAP_FILENAME='../obs1875/obs.emap', WARNING_REGION_FILENAME='warning.reg'

acis_extract, 'all.srclist', '1875', /EXTRACT_EVENTS, /PLOT

• The optional ENERGY_RANGE parameter defines the band over which statistics are computed; default is [0.5,8.0].

• The optional WARNING_REGION_FILENAME parameter names a CIAO region file that defines regions of the field on which sources will require special attention. AE will determine what fraction of the source events fall in the ``warning regions'', and report the fraction in the keyword WARNFRAC in obs.stats.

• The optional NEIGHBORHOOD_SIZE parameter specifies the minimum width/height (in arcseconds) of the source neighborhood that is extracted; default is 50.

• The optional keyword /REUSE_NEIGHBORHOOD directs AE to use any existing neighborhood.evt file it finds from a previous run, saving significant time for an observation with many events.

• If the optional parameter /ONLY_EDITED is set the only sources processed are those for which the extraction region file (extract.reg) appears to have been edited by DS9 (e.g. during the SHOW_REGIONS stage). This is merely a convenience for the situation where reprocessing a complete catalog would take a long time and making a list of the extraction regions you've edited would be a hassle.

E..2.3 Data Products

For each source the following files are produced:

{sourcename}/{obsname}/neighborhood.evt:

a FITS event list covering the immediate neighborhood of the source

{sourcename}/{obsname}/obs.psffrac:

a FITS file containing a table of PSF fractions at all the energies for which a PSF was computed.

{sourcename}/{obsname}/source.evt:

the events falling in the source extraction region

{sourcename}/{obsname}/obs.stats:

a FITS file containing keyword information about this observation of the source

Several interactive plots show characteristics of the source extraction; see our AE recipes (§7.1) for descriptions of each.