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It is possible for an observation to use 'mixed-modes'. Some scans could use binning mode and other scans could use phased-array mode.
Summary
For binned mode, the pulsar metadata is part of the SDM and can be handled with an extension of the standard SDM ingestion with additional fields in the database for the metadata.
For phased-array mode, the pulsar metadata is contained in the .ar and .cf PSRFITS files. In this case, it might be technically more feasible to extract the metadata from the PSRFITS files and place them in a metadata.json file that represents metadata per scan/subscan (IF?).
The PSRFITS files represent ancillary products of the execution block science product. They do, however, provide additional metadata for the execution block at the individual scan level.