Fermi Gamma-ray Space Telescope

Lightcurves

We are interested in the source intensity as a function of time. Because this lightcurve is produced for data exploration, we will work in detector count space. The gtbin tool can create lightcurves for both LAT and GBM data using all the data in the event list (the event file data type for LAT data, the TTE data type for GBM data). Thus energy and spatial selections should be made prior to generating the lightcurve with gtbin. For LAT data, the energy and spatial selection occurs initially when the event file is extracted from the FSSC database and then by using gtselect.

Once you choose the gtbin option ('LC' for lightcurve), and name the input and output files, you specify the time binning. You have three choices:

  • Linear temporal binning ('LIN')—you provide the start and stop times (in mission elapsed time—MET—described in the Time section) and bin duration.
  • Constant signal-to-noise ratio in each time bin (the 'SNR' option)—you provide the start and stop times and the value of the signal-to-noise ratio.
  • User specified time bins (the 'FILE' option)—you provide the name of the FITS file with the time binning. The gtbindef tool converts an ASCII file with the times into the properly formatted FITS file.

You can then plot the lightcurve stored in the output FITS file. For examples, see the 'Explore the LAT data,' 'Explore the LAT Data (Bursts),' and 'GBM Gamma-Ray Burst Analysis' threads.

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