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| 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 pairsis used to measure the energy of incident gamma rays. It measures the energy deposited by the electromagnetic shower that develops from the gamma ray after pair production. 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. | §2.2.2 |
| cat. / Cat. | (category) Papers involving the LAT Collaboration are assigned a category - 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) | |
| CTB | (Classification Tree Bill) |
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| term | definition | link |
|---|---|---|
| Earth limb / Earth's limb | The Earth is a bright emitter of gamma rays, due to cosmic rays interacting with the atmosphere. | |
| EBL | (Extragalactic Background Light) When used in gamma-ray astrophysics, EBL usually means the infrared-optical-ultraviolet light that fills intergalactic space, coming from all the stars that ever existed. Gamma rays can be absorbed by the EBL through the process of photon-photon pair production, in which a high-energy gamma ray collides with a low-energy IR-optical-UV photon to produce an electron-positron particle pair. | |
| EDISP | (energy dispersion) The energy dispersion is a measure of how accurately we can reconstruct the energy of a photon from the energy it deposits in the LAT calorimeter. The energy dispersion is a part of the LAT Instrument Response Functions (IRFs), and ; however information on the energy dispersion is not automatically taken into account in the Science Tools for standard LAT analysis. | Cicerone |
| effective area | The number of photons detected divided by the source flux. The LAT effective area is a function of photon energy and inclination angle. | |
| EGB | (Extragalactic Background) After accounting for known sources of gamma rays from individual sources and diffuse radiation within our Milky Way Galaxy, there is a residual component called the EGB. Some or most of the EGB is thought to originate from unresolved sources at large distances. | |
| EPO (group) | (Education and Public Outreach) | EPO group link |
| event | An "event" is a catch-all name for "things that the LAT detects" (although sometimes it is used specifically to mean photons). In practice, these are either photons or cosmic rays. | |
| event class | Events that are detected by the LAT are sorted into different classes based on how confident we are that the event is a photon. | Cicerone |
| Evo | Video conferencing software that has now been superseded by SeeVogh. | |
| exposure |
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| term | definition | link |
|---|---|---|
| L1Proc | (Level 1 Processing) | |
| LAT | (Large Area Telescope) The LAT is the main instrument on Fermi. The parts of the LAT are the Tracker, Calorimeter, and ACD. | |
| light curve | A light curve is generally a plot of the photon flux versus time. | |
| likelihood | Maximum likelihood analysis, likelihood for short, is the principal statistical analysis tool used in LAT analysis to evaluate significance of any signal. | |
| livetime | ||
| LLE | (LAT Low Energy) LLE is a loose event selection that starts at 30 MeV (while the standard LAT event classes start at 100 MeV). The LLE is background-dominated, so it is only appropriate for short, transient events such as gamma-ray bursts or solar flares. | |
| LMC | (Large Magellanic Cloud) The LMC is a small neighboring galaxy to our Milky Way. The same processes that produce gamma rays in our Galaxy produce a gamma-ray signal in the LMC detectable by the LAT. | |
| LPA | (LAT Physics Acquisition) |
M
| term | definition | link |
|---|---|---|
| M31 | M31, the Andromeda Galaxy, is the closest large spiral galaxy to our own. It is the only such galaxy to be seen as a gamma-ray source. | |
| MC | (Monte Carlo) | |
| merit / merit file | ||
| MET | (Mission Elapsed Time) Many missions record times in MET, which is the number of seconds since January 1, 2001. | A tool for converting from MET to dates |
| MIP | (minimum ionizing particle) | |
| MOC | (Mission Operations Center) | |
| MSP | (millisecond pulsar) MSPs are generally considered to be "recycled" pulsars, neutron stars in binary systems, spun up by accretion from their companion star. As the name implies, MSPs have rotation periods in the millisecond range. Think kitchen blender speed, only on an object the size of the Washington Beltway having a mass 1.5 times that of our Sun. | |
| multimessenger | Multimessenger studies include data from instruments that detect things other than light. For instance, one might combine LAT data (photons) with neutrinos, cosmic rays, gravitational waves, etc. | |
| MW | (multiwavelength) Multiwavelength studies are conducted across different wavelengths and energies. For instance, one might combine LAT data (MeV-GeV) with optical, radio, IR, TeV, etc. data. |
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| term | definition | link |
|---|---|---|
| TDRSS | (Tracking and Data Relay Satellite System) TDRSS is an array of satellites in geosynchronous orbit. These satellites relay data from missions like Fermi to ground stations. | |
| TEM | (Trigger Event Tower Electronics Module) | |
| TGFs | (terrestrial gamma-ray flashes) TGFs are very short (less than 1 millisecond) flashes of low-energy gamma rays produced near thunderstorms on Earth. The large electric fields of thunderstorms accelerate electrons to high enough energies that they can produce gamma rays as they interact with air molecules. | |
| theta | ||
| ToO | (Target of Opportunity) | more info |
| transient | ||
| transient (event class) | ||
| TRKTKR | (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). | §2.2.1 |
| Trunc64 | ||
| TS | (test statistic) |
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