Fermi Gamma-ray Space Telescope

Target of Opportunity Observations

Please note: 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. Please see this page for details regarding this event and of Fermi's new observing strategy. The following text has been preserved for historical/informational purposes.

The Fermi Project Scientist (or her/his designee) may declare a Target-of-Opportunity (TOO) pointed observation if warranted, prompted by observer request. If you are in the process of developing a TOO request, please consider submitting a preliminary TOO request so that the project can help in the planning process.

The Project Scientist will consult with the FSSC regarding the feasibility and impact of a TOO observation. The TOO observation will be implemented within 6 hours after the Project Scientist authorizes the observation; the actual time will likely be much shorter. Not all TOO observations will need to be implemented as soon as possible, and you may request implementation during the next business day.

In the process of evaluating the impact of a TOO, the Project Scientist will review any scheduled or ongoing multiwavelength observations that have been reported to the FSSC multiwavelength reporting page, and attempt to minimize the impact. If the Project Scientist deems those scheduled observations to be of higher priority than the TOO, they will likely deny the request.

Please note that survey mode observations, including the newly implemented galactic center biased observing mode, provides coverage of the entire sky every 3 hours. This ensures continuous monitoring of all sources on timescales greater than 3 hours, guaranteeing gamma-ray data for a wide range of studies. During this three-hour period, each region of the sky will be observed for around 30 minutes, as a result of the very wide field of view of the LAT (>2.5 sr). Sky survey data from the LAT are likely to address the needs of the great majority of studies, including those that would commonly require TOO observations at other types of facilities.

The scientific motivation for TOO pointed mode observations with Fermi must therefore be very compelling and strongly justified. However, we encourage you to submit a preliminary TOO Request early, even before the scientific justification is complete, when planning a TOO so that we can work with you to determine the best observing strategy for your specific request.

A pointed mode observation can provide around a factor of two increase in sensitivity for a given time interval. Due to Fermi's low-Earth orbit, nearly all pointed observations will be interrupted by Earth occultation. Pointed observations will also have a detrimental effect on coverage of the rest of the sky, which may hurt multiwavelength campaigns and uniformity of time monitoring studies. The project can determine if pointed mode observations are necessary or if a modified survey strategy would fit your needs. Please contact the project for more details or submit a preliminary TOO request.

Standard LAT data release policies apply to TOO observations. The LAT team will release high-level data (lightcurve etc) on a sample of sources and on any object which flares above 1e-6 /cm^2/s (E>100 MeV). All LAT photon event data including the TOO and monitored sources is released publicly within days of acquisition.

TOO Resources

Last updated by: Joseph Eggen 10/15/2019