Fermi Gamma-ray Space Telescope

Cicerone: Data - Data Access


The LAT event data are restricted to the LAT team during Phases 0 and 1, the first ~14 months of the Fermi mission. During these Phases, the LAT team will be turning on and calibrating their detector, and carrying out an all-sky survey. Summary information, such as spectra and lightcurves of ~23 sources of interest to the scientific community and of bright transient sources, is regularly released to the general community. All the LAT event data will become public after the beginning of Phase 2.

GBM burst event data will be public from the beginning of the mission, although systematic uncertainties will most likely be greater during Phases 0 and 1.

Extracting the Data

The public LAT data can be accessed using the FSSC data server. On this webpage you specify the desired selection criteria such as time range and spatial region. Use of this webpage should be self-explanatory. Soon after you submit the request you will be presented with a webpage with links to the event and spacecraft files that you can then ftp back to your computer. Information on the selection criteria are included in a FITS header in the event file; the Fermitools use this selection information.

The event files can be very large. If you use the ftp function built into your web browser, ensure that the browser's cache is large enough to accommodate the files; otherwise only part of the file may be read.

The GBM burst event data is available through Browse tables specific to Fermi. The data from each burst are packaged together with background files and response matrices.

Further Data Selections

Further data selections can be performed on the LAT event file that was extracted from the FSSC or HEASARC websites by using the gtselect tool. More refined selection criteria are available using this tool than when extracting the data through the data extraction website. The additional selection criteria are recorded in a FITS header in the resulting event file.

Subsets of the GBM TTE data are selected when binning these data for lightcurves or count spectra using gtbin.

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