Versions Compared

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

...

termdefinitionlinks
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

LAT Instrument Paper

cat. / Cat.(category)
Papers involving the LAT Collaboration are assigned a category - I, II, and III. 
category explanation
catalogA 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 charged, high-energy particles from outer space.
Mostly are protons, some are electrons and heavier elements. They range from a few MeV to EeV.
Cosmic rays are the main source of background that the LAT detects. 

 
CTB(Classification Tree Bill) 

...

termdefinitionlink
Earth limb / Earth's limb

The Earth is a bright emitter of gamma rays, due to cosmic rays interacting with the atmosphere.
When the Earth is in the LAT field of view, the part of the Earth that is visible is known as the Earth limb.
Almost all LAT analysis needs to minimize the contribution from the Earth limb.
(see zenith angle cut

 
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 areaThe number of photons detected divided by the source flux.
The LAT effective area is a function of photon energy and inclination angle.

FSSC page
LAT performance page

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
eventAn "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 classEvents 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.
see also "SeeVogh" 

 
exposure  

...

termdefinitionlink
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.
For pulsars, a light curve is usually a plot of the photon flux versus the pulsar phase. 

 
likelihoodMaximum 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

termdefinitionlink
M31M31, 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.
 
multimessengerMultimessenger 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. 
 

...

termdefinitionlink
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

LAT Instrument Paper

Trunc64  
TS(test statistic) 

...