...
| term | definition | links |
|---|---|---|
| ACD | (Anti-Coincidence Detector) The ACD is the collection of scintillating tiles that detect charged particles, and is crucial to background rejection. The ACD covers the tracker (the part of the LAT that converts gamma rays into electron-positron pairs and then tracks these pairs' trajectories). Charged particles will also register as signals in the tracker, so the ACD is used to determine if a signal is actually a charged particle and not a gamma ray. If an ACD tile has a "hit" (detects a charged particle) that lines up with a signal, then that fact is used to "veto" the signal (i.e., declare that it's not a gamma ray). | |
| Acceptance | Defined as the effective area integrated over the solid angle subtended by the field of view (units: m^2 sr). It is a measure of the "effective volume" of the entire field of view. | LAT performance page |
| AGN (group) | (Active Galactic Nuclei) | AGN group page |
| ARR | (Autonomous Repoint Request) When the Gamma-ray Burst Monitor (GBM, the secondary instrument on Fermi) detects a gamma-ray burst (GRB) that is especially bright or high-fluence (i.e., emitting many photons over a period of time), it sends a message to the spacecraft to maneuver itself so that the GRB is close to the center of the LAT field of view for 2.5 hours (previously, 5 hours). This allows the LAT to get good observations of the GRB for a longer period of time than it would otherwise be able to obtain. | more info |
| ASP | (Automated Science Processing) A set of automated science analyses runs on the data when it comes to the ground, to detect sources that are changing rapidly in time. These are often gamma-ray bursts (GRB), which are exploding transient phenomena, or active galactic nuclei (AGN), which can sometimes flare and emit more gamma rays than they normally do for short periods of time. | ASP Data viewer |
| ATel | (Astronomer's Telegram) | |
| ATS | (Absolute Time Sequence) A series of spacecraft and/or instrument commands that are loaded on the Fermi spacecraft. | |
...
| term | definition | links |
|---|---|---|
| C&A (group) | (Calibration and Analysis) | C&A group page |
| CAL | (Calorimeter) The calorimeter is the part of the LAT that records stops each electron-positron pair and records its energy, after the tracker has converted the photons into these pairs. The main purpose of the calorimeter is to record the energy, but the CAL is also able to roughly track the trajectories. Physically, it is located at the bottom of the LAT. It is made of cesium iodide (CsI) crystals. | |
| cat. / Cat. | (category) Papers written by the LAT collaboration are assigned a category out of I, II, and III. | category explanation |
| catalog | A catalog is a paper that contains information on all of a certain type of object that the LAT has observed. Catalogs can be more general ("all objects in the sky that emit gamma rays") or more specific ("all pulsars"). | LAT catalogs |
| Catalog (group) | Catalog group page | |
| clean (event class) | ||
| CR | (cosmic ray) Cosmic rays are the main source of background that the LAT detects. | |
| CTB | (Classification Tree Bill/Best) | |
...
| term | definition | link |
|---|---|---|
| TDRSS | (Tracking and Data Relay Satellite System) | |
| TGFs | (terrestrial gamma-ray flashes) | |
| theta | ||
| ToO | (Target of Opportunity) | more info |
| transient | ||
| transient (event class) | ||
| TRK | (Tracker) The Tracker is a part of the LAT whose purpose is twofold: 1) To convert gamma rays into electron-positron pairs, and 2) To track these pairs of charged particles through the instrument in order to figure out where the original gamma ray came from. The Tracker is made of alternating layers of tungsten foils (to convert the gamma rays) and silicon strip detectors (to track the pairs), arranged in 64 columns (8 by 8). | |
| Trunc64 | ||
| TS | (test statistic) |
...