Bad Pixel File (bpix3.fits)
The bad pixel file consists of a single FITS format file for each observation that records the bad pixel information for the observation. The bad pixel information is used in catalog processing to flag for removal the effects of detector bad pixels during the observation.
FITS HDUs (CXC Data Model blocks):
- ACIS: BADPIX0, BADPIX1, BADPIX2, BADPIX3, BADPIX4, BADPIX5, BADPIX6, BADPIX7, BADPIX8, BADPIX9
- HRC: BADPIX
![[NOTE]](../../imgs/note.png)
For ACIS, the bpix3.fits file is the same as the bpix1.fits file from the Chandra Data Archive. The HRC bpix3.fits may have a newer degap correction applied than the bpix1.fits version.
The bad pixel FITS file is named: 〈i〉〈s〉〈obs〉_〈obi〉N〈v〉[_〈c〉]_bpix3.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.
![[TIP]](../../imgs/tip.png)
Bad pixel files are used in nearly all data processing and data product extraction. In CIAO, setting the bad pixel file in the analysis reference data library before starting analysis with a corresponding event file is advised, even if a specific tool does not wind up using it.