Analysis Threads
The analysis threads are step-by-step guides to various types of analyses that you can do with Fermi data. You should have basic understanding of the analysis tools and the essentials of LAT analysis.
Note: These threads are based on the use of Pass 8 data. A description of modifications made for the Pass 8 data set is available here.
Many of the threads have been migrated to Jupypter notebooks in a repository on Github, which can be run interactively, and the HTML versions will no longer be updated. Links on this page have been updated accordingly and will open in a new tab on Github.
Available Analysis Threads
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These threads cover the basics of obtaining LAT data, applying selection cuts, and a few simple types of analyses.
Tutorial Name Description Extracting LAT Data Obtain data from the LAT data server. Data Preparation Perform selection cuts using the Fermitools. Explore LAT Data Explore and manipulate LAT data using some simple techniques. Explore LAT Data (for Burst) Examine LAT data for a gamma-ray burst. Using LAT All-sky Weekly Files Generate an all-sky data set that is useful for several kinds of analysis. -
These threads describe source analysis, especially maximum likelihood fitting, using both the standard command line versions of the tools and the Python interface.
Tutorial Description Binned Likelihood Perform a binned likelihood analysis, the preferred method for most types of LAT analysis. Unbinned Likelihood Perform an unbinned likelihood analysis, the preferred method for time series analysis of LAT data, where the number of events in each time bin is expected to be small. Likelihood Analysis with Python An unbinned analysis using Python. Summed Likelihood Analysis with Python Joint likelihood on two data selections using the same XML model. Binned Likelihood with Energy Dispersion Binned likelihood with energy dispersion using Python. Upper Limits with Python Determine an upper limit on the GeV emission from Swift J164449.3+573451. Extended Source Analysis Based on the one performed on Centaurus A by the LAT team (uses Python). LAT Aperture Photometry Analysis A non-likelihood (model independent) approach to measuring a source's flux. Pulsar Gating Remove the flux of a bright pulsar from a region of interest. Evaluating Effective Area Systematics Deal with systematic uncertainties when performing LAT analysis. Generating Solar and Lunar Templates Use the Solar System Tools to create a template of the Solar and Lunar emission for likelihood analysis. -
Gamma-ray burst (GRB) analysis can be done with both LAT and GBM data.
Tutorial Name Description LAT GRB Analysis Extract and model a LAT GRB observation. GRB Analysis Using GTBurst Guide to the gtburst GUI for GRB and solar flare analysis of GBM and LAT data. GBM Data Tools tutorials Tutorials on how to use various aspects of the GBM Data Tools. -
The pulsar community generally relies on non-Fermi specific tools like TEMPO2, PINT, and PRESTO for the bulk of pulsar analysis and only use the Fermitools for initial data reduction. The following analysis threads only offer basic functionality.
Tutorial Name Description Pulsar Analysis Tutorial A two-part video tutorial showing how to analyze pulse signals in LAT data. Ephemeris Computation Utility Use gtephemto get the best ephemeris available in a pulsar database for a given pulsar and instant of time.Arrival Time Correction Use the gtbarytool to perform a barycentering time correction to an event file using spacecraft orbit files. -
These tutorials demonstrate using the observation and orbit simulation tools, which might be useful to make a realistic assessment of the detection significance achievable within a given time interval or the ability to constrain source model parameters for a given source intensity.
Tutorial Name Description Observation Simulation Tutorial Simulate a Fermi observation using the gtobssimapplication.Sources available to gtobssim Examples of the types of sources that are possible to simulate using gtobssim.Orbit Simulator Tutorial Run gtorbsim, a spacecraft attitude calculator. -
These are some potentially useful resources for data analysis.
Name Description Video Tutorials Demonstrate standard analysis techniques and basic analysis software usage. Fermitools Reference Contains Unix "man page"-style guides for each tool. Using Pass 8 Data Explains the modifications made for the Pass 8 data set. Maximum Likelihood Methodology Detailed description of the maximum likelihood methodology. Spectral and Spatial Model Definitions Describe the models available to use with gtlike.XML Model Examples Example model definitions for likelihood fitting. LAT Background Models Models of Galactic diffuse and isotropic emission.