Fermi Gamma-ray Space Telescope

LAT Target of Opportunity Observations

The Fermi Project Scientist (or his/her designee) may declare a Target-of-Opportunity (TOO) pointed observation if warranted, prompted by observer request. Because of the large field of view of the instruments and the characteristics of the gamma-ray sky, this is anticipated to happen infrequently (see below) when in the standard sky survey observing mode.

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, the current default, 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.

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,

Standard LAT data release policies apply to TOO observations. The LAT team will release high-level data (lightcurve etc) on a sample of 23 selected 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 publically within days of acquisition.

TOO Resources