...
| 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 |
F
| term | definition | link |
|---|---|---|
| F2F | Face-to-face | |
| FA | (flare advocate) Flare Advocates are volunteers who watch the LAT gamma-ray sky on one-week shifts, looking for flares of known or unknown gamma-ray sources. | Flare Advocates Confluence Main Page |
| FITS / fits / .fits / fit (file type) | (Flexible Image Transport System) FITS files are often used in astronomy, and are made of one or more HDUs (Header and Data Unit). Each HDU has a header with general information about the file, the instrument, etc., as well as a table or image. Public LAT data is always (?) distributed as FITS files. | FITS Support Office |
| FltOps | (Flight Operations) | |
| FOT | (Flight Operations Team) The FOT is the staff at the Mission Operations Center (at NASA Goddard), which controls the spacecraft. The FOT is responsible for, among other things, inputting special maneuvers such as TOOs. | |
| FOV / FoV | (field of view) The FOV is the useful solid angle on the sky seen by a Fermi instrument at one time. The LAT FOV is about 2.4 steradians; the GBM FOV is about 8.5 steradians (everything in the sky not blocked by the Earth). | |
| front | The front half of the LAT is the 12 layers of thinner tungsten (which converts the photons into electron-positron pairs) that are at the top of the LAT. Photons that convert in this region tend to better reconstructed than photons that convert in the back (or bottom). It is possible to only use the front or back events on their own in an analyses, but generally, the fact that events are either front- or back-converting is automatically accounted for in the analysis software and instrument response functions. | |
| front-converting | Front-converting events are photons that are converted into electron-positron pairs in the top portion of the LAT (see front). | |
| FSRQ | (Flat Spectrum Radio Quasar) FSRQs, along with BL Lac objects, make up the sub-class of Active Galactic Nuclei called blazars, the most common type of extragalactic source seen by the LAT. | |
| FSSC | (Fermi Science Support Center) | Fermi Science Support Center |
| FSW | (Flight Software) | |
| FT1 (file) | FT1 files are the LAT public data files with information on each individual photon. | |
| FT2 (file) | FT2 files are the LAT public data files with information on the spacecraft (where it is, where it's pointing, etc.). | |
| FTOOLS | A package of tools to manipulate FITS files. | FTOOLS main page |
| FUG | (Fermi Users Group) An advisory panel of scientists from gamma-ray and related disciplines. The FUG represents all scientists who use Fermi data. | Fermi Users Group |
| fv | (Fits Viewer) fv is a program to view FITS files. | fv main page |
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| term | definition | link |
|---|---|---|
| HEASARC | (High Energy Astrophysics Science Archive Research Center) | HEASARC NASA page |
| HMB or HMXB | (High-mass binary/High-mass X-ray binary) HMB systems consist of a compact object (neutron star or black hole) orbiting a high-mass normal star. The LAT sees a number of HMB systems, with orbital periods ranging from 4.8 hours (Cygnus X-3) to about 5 years (Eta Carinae). |
I
| term | definition | link |
|---|---|---|
| IEM | Interstellar Emission Model | |
| IGRB | Isotropic Gamma Ray Background | |
| IRF | (Instrument Response Function) | Cicerone |
| ISOC | (Instrument Science Operations Center) |
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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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| term | definition | link |
|---|---|---|
| zenith | The point on the sky that is opposite to the Earth for the Fermi spacecraft. |  (diagram from Wikipedia) (imagine the person is Fermi) |
| zenith angle cut | The zenith angle cut defines the maximum zenith angle for all the photons that will be used in an analysis. The zenith angle cut is used to cut down on the emission from the Earth limb (the part of the Earth that is in the LAT field of view). | |
AG component