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FSSC: Fermi Data : Data Server Caveats

Caveats About the Fermi Data Server

Here we provide a listing of known issues, errors, or other conditions with the FSSC's LAT data server that may affect the science data or the delivery of data.

Query Results

If END is used for the time entry, the LAT events and spacecraft files use the same time for that end of the data file.

Weekly Files

On March 14 2022, the LAT data server transition to new hardware. As part of the transition and to make use of the new hardware, parts of the backend software were extensively updated, including the software that ingests new LAT data and creates the weekly files. The entire LAT data set was ingested again using the new routines (which are also much faster).

If you have a job that regularly downloads the weekly files (e.g., using rsync), it may see all the weekly files as updated and download them all again. The difference between the old and new sets are minor:
  • The photon and event weekly files are now sorted by time. Previously, this was not always the case. New data was added to weekly files in the order it was received, which was not always time-ordered. This is most evident in the files since the last reprocessing in 2018.
  • Different CREATOR and VERSION values in the FITS header.
  • The DATE keyword is different since it represents the file creation time.
  • DATE-OBS and DATE-END, which specify the calendar dates covered by the file, were fixed to match TSTART and TSTOP, which are the dates in Mission Elapsed Time. Previously, they were not correct and were taken from the last run file ingested.
  • CHECKSUM will be different, although DATASUM may be the same.
  • There may be some last decimal digit differences in the ONTIME keyword (a floating-point number).
The old weekly files are still available in the archive.

Please contact the FSSC helpdesk with any questions.