Overview: LAT Data Analysis Tools

The following set of Fermi-specific tools are used to analyze LAT data; some tools, such as gtbin, can also process GBM data products. Tool groups include: General, Likelihood, Gamma-ray Burst Analysis, Pulsar Analysis, and Observation Simulation.

General:

   gtselect

Creates a new filtered FITS file based on cuts applied to the values in each row of an input event file. Enablies more detailed selections to be made on data obtained from the data server.

   gtbin

Computes the counts maps for use in a binned likelihood analysis; bins are 'cubes' in latitude, longitude, and log(energy).

   gtbkg

Creates a background spectrum file for use in Xspec analyses.
Print Version cube_display generates an exposure map, or a set of exposure maps for different energies, from a livetime cube written by gtltcube.

Replaces the old gtexpcube application from the map_tools package; also replaces the "on-the-fly" binned exposure map calculation that was provided by gtsrcmaps.

Accounts for the phi-modulation of the effective area for the irfs that implement this dependence (e.g., P6_v11_* and P7*_V4); also includes effects of the livetime-fraction dependent efficiency that has been available for the P6_V3_DIFFUSE irfs and will continue to be available in future irfs.

   gtltcube

Integrates the livetime as a function of sky position and off-axis angle, using the spacecraft data file and the time range and GTI selections in the event file. The sky is represented using a nested HEALPix array.

   gtltsum

Adds together livetime cubes produced by gtltcube.
Given a counts light curve prepared using gtbin for a specific location on the sky, this tool computes the exposure (cm2-s) associated with each time bin, allowing a light curve in photons/s to be computed.

   gtmktime

Create Good Time Intervals (GTIs) based on selections made on the spacecraft data file variables.

   gtpsf

Calculates the effective point spread function as a function of energy at a given source location, averaged over an observation.

   gtvcut

Prints a summary of the Data Sub-Space keywords.
Likelihood:

   gtdiffrsp

Computes the event-specific response for each diffuse source in the input source model. A column containing these data is added to the event file for each source.

   gtexpmap

Computes the exposure maps for use in an unbinned likelihood analysis.

   gtfindsrc

Optimizes a point source location using the likelihood test-statistic.

   gtlike

Enables LAT data to be analyzed using an unbinned or binned formulation of the log-likelihood.

   gtltcube

Integrates the livetime as a function of sky position and off-axis angle, using the spacecraft data file and the time range and GTI selections in the event file. The sky is represented using a nested HEALPix array.

   gtmodel

Creates a model counts map by summing up convolved source maps that have been scaled by the spectral parameters given in the source model XML file.

   gtsrcmaps

Convolves components of the specified source model with the instrument response for a given observation. The geometry in sky and energy coordinates of the output maps match that of the input counts map.

   gttsmap

Computes a test statistic map for source localization and detection in an unbinned likelihood analysis.
Computes source component probabilities for event data.
Enables you to create XML source model files for use as input to the Fermi likelihood estimator program. Tip: Use ModelEditior to check your XML. Regardless of what editing tool is used to create a source model XML file, you can use ModelEditor to validate the file; just load the xml file into ModelEditor, which will generate errors if the format is not correct for use with the Science Tools.
Source Identification:

   gtsrcid

Creates a counterpart candidate catalog by correlating the objects from a list of detected sources with the objects of an existing source catalog, such as the 3EG catalog.
Gamma-ray Burst Analysis:

   gtbin

Bins an event list in time, energy, or space, and results in spectra, lightcurves or a count map.

   gtbindef

Utility used to read in an ASCII file with the time or energy bin definitions, and produce the FITS file, which can be used by gtbin.

   gtrspgen

Creates a standard FITS file (rmf) required to analyze a binned spectrum.

   gtburstfit

Analyzes burst light curves by applying a Bayesian algorithm to determine the optimum set of blocks to follow the burst profile shape; blocks may also be used by gtburstfit to construct a pulse model, which gtburstfit can fit to the data.
Pulsar Analysis:

   gtpsearch

Searches for pulsation frequencies near a known, or estimated reference frequency.
   gtpspec Searches for pulsations in a wider range of frequencies, using the Discrete Fast Fourier Transfer (FFT) technique to compute power spectrum density.
   gtptest Applies all of the statistical tests available with the gtpsearch application to a series of pulse phase values stored in given event files.

   gtpphase

Operates on an event file to compute the spin (pulse) phase for the time of each event, and writes this phase to the PULSE_PHASE column of the event file.

   gtophase

Operates on an event file to compute the orbital phase for the time of each event, and writes this phase to the ORBITAL_PHASE column of the event file.

   gtephem

Presents the user with the best ephemeris available in a pulsar database for a given pulsar and instant of time.

   gtpulsardb

Creates, filters, and/or combines pulsar ephemerides database files.

   gtbary

Performs a barycentering time correction to FITS files using GLAST orbit files.
Observation Simulation:

   gtorbsim

Generates spacecraft orbit and attitude data for a variety of pointing strategies.

   gtobssim

Generates photon events from astrophysical sources and processes those photons according to the specified instrument response functions.

Last updated by: Chuck Patterson 04/12/2011