7.3 Other General Parameters

In the sections below where each AE stage is described, there are several parameters besides catalogs and source lists which commonly occur.

obsname:

a string that identifies an observation (usually an ObsId e.g. ``1875''); it will name a sub-directory created for each source.

EXTRACTION_NAME

an optional string or string array that identifies a set of extraction parameters. If supplied, the AE output files are structured with an extra directory level using the specified name(s). For example, if the observer wished to perform the extraction twice, with two different sets of PSF fractions, then EXTRACTION_NAME could be used to put the output from the two extractions in separate directories. Similarly, data products produced by merging multiple extractions can be named via the MERGE_NAME parameter to the MERGE_OBSERVATIONS Stage (§7.16).

obsdata_filename:

the file name of the single-observation event list you wish to use for extraction. This manual will not attempt to discuss the various recipes observers use to prepare ACIS data for spectral extraction. The only event list columns used by AE are TIME, CCD_ID, CHIPX, CHIPY, DETX, DETY, X, Y, PI, and ENERGY; discarding the other columns will reduce AE run times.

The event data must be in the tangent plane coordinate system of the observation, not ``reprojected'' to some other observation (§7.5). When performing an AE extraction for spectral analysis, we recommend that the event list should NOT be strongly filtered by energy, and that ``flaring pixels'' should be retained. The spectra can be more correctly band-limited later during spectral analysis.

emap_filename:

the file name of a single-observation exposure map that is aligned with the event data, that represents any masking done to the event data, and that has a field of view corresponding to the event data you're extracting. The CXC provides threads and scripts for constructing exposure maps. We use the tool ae_make_emap (§7.20). It's unclear whether the energy band used in computing the exposure map has any significant effect on the results. AE was written with the expectation that the exposure map has units of $seconds \times cm^2 \times counts/photon$ (i.e. the normalize="no" option was supplied to mkexpmap). Note the exposure maps supplied to the EXTRACT_SPECTRA and EXTRACT_BACKGROUNDS stages of AE are integrated over the source and background extraction regions in order to derive appropriate scaling for the background spectrum. The integrals alone determine the scaling; the EXPOSURE keywords in the two event lists are ignored.

There is no specific binning requirement for the exposure map, however keep in mind that in AE both point source masks and background regions are ultimately defined as regions corresponding to sets of exposure map pixels rather than as geometric regions (e.g. ds9 region files). We recommend an exposure map pixel size of 1 sky pixel or smaller, particularly if the tools ae_better_masking or ae_better_backgrounds are to be used (§7.12.2).