For each stack containing more than one observation interval, the Pre-Calibrate/Pre-Detect pipeline is run to prepare for the fine astrometry step. The goal of this pipeline is to identify bright sources in each of the observations. These sources are later used in the fine astrometry correction step.
Reprocess the datasets with the same CALDB
A new bad pixel file is created to ensure that all observation-specific hot pixels and afterglow events are included in the mask, and excluded from the analysis.
The OBI is then reprocessed to apply the latest calibration—gain, ACIS time-dependent gain, ACIS charge transfer inefficiency (CTI), HRC degap, etc. A unique CALDB is used for catalog processing; it is frozen for the duration of the processing run so that the same calibration is applied to all the datasets in that version of the catalog. The same processing tools are used as in the Chandra Standard Data Processing pipeline: acis_process_events for ACIS data and hrc_process_events for HRC data.
Standard filtering is applied to the data to apply the good time intervals (GTIs) and remove bad events with bad grades or status flags. ACIS datasets are destreaked. Average dead time corrections are calculated for HRC datasets.
Run wavdetect to identify bright point sources
For each observation in a multi-observation stack, the wavdetect program is run with conservative parameter settings to identify bright point sources suitable for astrometrically matching the observations that comprise each observation stack.
Output data products
The Pre-calibrate pipeline produces only temporary files; no archive data products are generated.