Aspect Histogram File (ahst3.fits)
The aspect histogram file consists of a single FITS format file for each observation that records the histogram of aspect pointing and roll offsets during the observation. The aspect histogram is used in catalog processing to compute the response matrix averaged over the observation.
FITS HDUs (CXC Data Model blocks):
- ACIS: asphist0, asphist1, asphist2, asphist3, asphist4, asphist5, asphist6, asphist7, asphist8, asphist9
- HRC: ASPHIST
The ahst3.fits file is generated by the asphist tool, as users would in CIAO data analysis.
The aspect histogram FITS file is named: 〈i〉〈s〉〈obs〉_〈obi〉N〈v〉[_〈c〉]_ahst3.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, and 〈c〉 is the cycle. The optional discriminator identified in square brackets is included only for ACIS alternating exposure (interleaved) mode observations.