Fermi Gamma-ray Space Telescope

Aug 03, 2015

Fermi-LAT Data Issue

There was a small glitch in Fermi-LAT data processing that has caused problems with a small amount of LAT data. This involved a problem with the detector calibration constants used in the LAT data processing pipeline that affected all the data corresponding to UTC 2015-07-27 19:04:46.642804 to 2015-07-30 11:03:18.085494. Click here for more details.

The problem has now been identified and resolved, and the data are being correctly processed. The aforementioned bad data segment (amounting to about 64 hours) has been marked as BAD in the spacecraft files in the FSSC dataserver and will thus cause the bad time intervals to automatically be skipped if you use the standard data selections with gtmktime. So from today, any data downloaded can be used without concern (you will simply see a gap corresponding to the bad interval). If you downloaded data from the affected time interval before today, we recommend that you redownload the data to pick up the spacecraft file with the updated BAD intervals.

The data will need to be reprocessed with the appropriate calibrations before it can be marked as GOOD and used for science analysis. We anticipate that will happen next week, and we'll keep you posted on the details. If you intend to use data from the affected period, we strongly recommend that you redownload the data after it has been reprocessed.