Source Region Per-Observation Detections Exposure Map Files (regexp3.fits)
The source region exposure map consists of a single FITS format file for each source region of each observation that results from catalog processing, for each science energy band. A full resolution instrument map that covers the detected source region rectangular bounding box is generated at the equivalent monochromatic energy for each energy band, and the exposure map is computed by applying the aspect histogram sampled at 0.5 arcsec resolution and blocking in SKY coordinates. The blocking factor matches that used for the corresponding full-field image file. The rectangular SKY region filter is equal in size to the background region of interest (ROI) corresponding to the detected source region.
ACIS Region-of-Interest Exposure Map
The per-observation region exposure map FITS file is named: 〈i〉〈s〉〈obs〉_〈obi〉N〈v〉[_〈c〉]_〈r〉〈b〉_regexp3.fits
where 〈i〉 is the instrument designation, 〈s〉 is the data source; 〈obs〉 is the observation identification; 〈obi〉 is the observation interval identification; 〈v〉 is the data product version number; 〈c〉 is the cycle; 〈r〉 is the region ID, formatted as "rnnnn", where nnnn is the 4-digit region number, formatted with leading zeros; and 〈b〉 is the energy band designation. The optional discriminator identified in square brackets is included only for ACIS alternating exposure (interleaved) mode observations.