Fermi Gamma-ray Space Telescope

Frequently Asked Questions

    General

  1. When was Fermi launched?
  2. What was Fermi called before launch?
  3. Where can I find out about the Fermi Guest Observer (GI) Program?
  4. How can I get email notices of Fermi news, software releases, etc.?
  5. What if I have additional questions not covered here?
  6. Is there a list of published Fermi papers that I can consult?

    7. Observations

  7. How will I learn that Fermi has detected a burst?
  8. Are you currently accepting Target-of-Opportunity (ToO) requests?
  9. What is Fermi's observing schedule?

    10. Obtaining Data

  10. What data products are available?
  11. How do I request a file containing only the spacecraft data?
  12. How do I download the weekly spacecraft and data files without using a browser?
  13. How do I download the spacecraft file for the entire mission?
  14. How can I use the weekly spacecraft files to create a parital or entire mission long file?
  15. How do I download Fermi data from the AWS Cloud?

    16. Analyzing Data

  16. How do I obtain and install the current version of the data analysis tools?
  17. How do I get help with the Fermi data?
  18. I think I found a software bug. How do I report it?

  1. When was Fermi launched?

    Fermi was launched June 11, 2008.

  2. What was Fermi called before launch?

    GLAST -- Gamma-ray Large Area Telescope.

  3. Where can I find out about the Fermi Guest Observer (GI) Program?

    See the GI Program page.

  4. How can I get email notices of Fermi news, software releases, etc.?

    Subscribe to the Fermi mailing lists.

  5. What if I have additional questions not covered here?

    Submit any questions through the FSSC helpdesk.

  6. Is there a list of published Fermi papers that I can consult?

    See the Fermi publications page.

  7. How will I learn that Fermi has detected a burst?

    Subscribe to the GCN (Gamma-ray burst Coordinates Network). When either the LAT or the GBM detects a burst, a series of messages will be sent to the ground through TDRSS, resulting in GCN Notices that are fixed format messages disseminated by e-mail, page or internet socket. Additional Notices will be sent out as a result of ground processing. In addition, as a result of further ground processing, the instrument teams may send out GCN Circulars, free format messages relaying information such as burst durations, fluences, spectral parameters, etc. Finally, check the GRB page on the FSSC website for links to other sources of burst information.

  8. Are you currently accepting Target-of-Opportunity (ToO) requests?

    No. On March 16 2018, the spacecraft suffered a mechanical failure and can no longer move one of its solar arrays. While Fermi was able to resume normal operations quickly, ToOs will not be done for the forseeable future.

  9. What is Fermi's observing schedule?

    Check the posted observing timeline.

  10. What is data products are available for download?

    Check the data products page.

  11. How do I request a file containing only the spacecraft data?

    You may download the spacecraft data file directly from the LAT data server.

    Put any coordinates and radius (or leave them blank) and select the time range that you are interested in (for example: 2008-08-04T15:43:37 to 2009-09-04T08:41:20 (239557417 to 273746480 seconds Mission Elapsed Time)). You can also enter "start, end" for the times.

    Make sure that the box for "Spacecraft data file" is checked and the other are not checked. Then click on "Start Search". The spacecraft data file returned will be valid for the entire sky.

  12. How do I download the weekly spacecraft and data files without using a browser?

    You can use wget to download the weekly files. For the weekly photon files, use the following command:

    wget -m -P . -nH --cut-dirs=4 -np -e robots=off \
    https://heasarc.gsfc.nasa.gov/FTP/fermi/data/lat/weekly/photon/

    and for the weekly spacecraft files, use:

    wget -m -P . -nH --cut-dirs=4 -np -e robots=off \
    https://heasarc.gsfc.nasa.gov/FTP/fermi/data/lat/weekly/spacecraft/

    You may wish to update the mission-long spacecraft file instead.

  13. How do I download the spacecraft file for the entire mission?

    The mission-long spacecraft file is available at the FTP site:
    https://heasarc.gsfc.nasa.gov/FTP/fermi/data/lat/mission/spacecraft/

  14. How can I use the weekly spacecraft files to create a parital or entire mission long file?

    Download the weekly files you want as (see above). You can use the -N option and wget will skip any files that you already have unless the timestamp on the remote file is newer.

    Create a text file that lists all the spacecraft files (I'm assuming you're in the directory with the weekly files):

    ls lat_spacecraft_weekly_w*.fits > weekly.list

    Merge the files with ftmerge:

    ftmerge @weekly.list lat_spacecraft_weekly_merged.fits lastkey='TSTOP,DATE-END' clobber=yes

    The lastkey parameter will copy the stop times from the last file. Otherwise, it just copies everything from the first file.

    This doesn't update the checksum (so ftverify will give a warning) or modify other header keywords, but that shouldn't affect analysis. You can fix those with ftchecksum and fmodhead if you wish.

  15. How do I download Fermi data from the AWS Cloud?

    To provide an alternate means of data access, the HEASARC has mirrored much of its archive (including Fermi data) to Amazon Web Services (AWS) cloud storage. Note that the update frequency between the HEASARC and AWS varies. GBM trigger/burst data files are synced to AWS shortly after they are archived at the FSSC. LAT weekly files are updated every Thursday at 1am ET, and GBM daily data products are not currently mirrored. The HEASARC has instructions describing how to access data in the AWS cloud.

    Fermi users may want to download specific data directories, e.g., for a GBM trigger. This can be done using AWS command line utilites or with curl/wget.

    The AWS command line utilities can be installed with homebrew on macOS and Linux.

     brew install awscli

    See the AWS Getting Started Guide for other ways to install the CLI tools and their usage.

    As an example, the data for the trigger bn250101395, which is available at the HEASARC URL https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250101395

    can be fetched using: 

    aws s3 sync s3://nasa-heasarc/fermi/data/gbm/triggers/2025/bn250101395 bn250101395 --no-sign-request

    which will create the local directory bn250101395 and copy the contents of the remote directory into it. In this case, that will be the current, previous, and quicklook directories and their GBM data files. Running the command again will just download any new files.

    Similarly, the LAT weekly photon files can be downloaded using: 

    aws s3 sync s3://nasa-heasarc/fermi/data/lat/weekly/photon photon --no-sign-request

    If you cannot or do not want to install awscli, here is an example of doing the same thing using curl and wget in the bash shell: 

    url="s3://nasa-heasarc/fermi/data/gbm/triggers/2025/bn250101395/"; \
curl -s "https://$(echo "${url#*://}" | cut -d/ -f1).s3.amazonaws.com/?list-type=2&prefix=$(echo "${url#*://*/}" | sed 's#/*$#/#')" \
  | grep -Eo '<Key>[^<]+' \
  | sed "s#<Key>#https://$(echo "${url#*://}" | cut -d/ -f1).s3.amazonaws.com/#" \
  | wget -i - -P "$(basename "${url%/}")"

    You can replace the URL string with the LAT photon file one used above to download all the photon files.

  16. How do I obtain and install the current version of the data analysis tools?

    See the Fermitools dowload page.

  17. How do I get help with the Fermi data analysis?

    Start with Fermitools documentation. If you encounter trouble running the tools, please check the Troubleshooting and Error Reporting pages. If you still need assistance, submit questions through the FSSC helpdesk.

  18. I think I found a software bug. How do I report it?

    Please check the Troubleshooting page and the Github trackers listed on the Error Reporting page to see if it has already been reported. If not or if you have additional information about the bug, following the error reporting procedures given there.