Gamma-ray Large Area Space Telescope Large Area Telescope Research Articles

The Gamma‐Ray Albedo of the Moon

We use the GEANT4 Monte Carlo framework to calculate the γ-ray albedo of the Moon due to interactions of cosmic-ray (CR) nuclei with moon rock. Our calculation of the albedo spectrum agrees with the EGRET data. We show that the spectrum of γ-rays from the Moon is very steep with an effective cutoff around 3-4 GeV (600 MeV for the inner part of the Moon disk) and exhibits a narrow pion-decay line at 67.5 MeV, perhaps unique in astrophysics. Apart from other astrophysical sources, the albedo spectrum of the Moon is well understood, including its absolute normalization; this makes it a useful standard candle for γ-ray telescopes. The steep albedo spectrum also provides a unique opportunity for energy calibration of γ-ray telescopes, such as the forthcoming Gamma Ray Large Area Space Telescope (GLAST). Since the albedo flux depends on the incident CR spectrum, which changes over the solar cycle, it is possible to monitor the CR spectrum using the albedo γ-ray flux. Simultaneous measurements of CR proton and helium spectra by the Payload for Antimatter-Matter Exploration and Light-Nuclei Astrophysics (PAMELA), and observations of the albedo γ-rays by the GLAST Large Area Telescope (LAT), can be used to test the model predictions and will enable the LAT to monitor the CR spectrum near the Earth beyond the lifetime of the PAMELA.

Environmental tests of the flight GLAST LAT tracker towers

The Gamma-ray Large Area Space telescope (GLAST) is a gamma-ray satellite scheduled for launch in 2008. Before the assembly of the Tracker subsystem of the Large Area Telescope (LAT) science instrument of GLAST, every component (tray) and module (tower) has been subjected to extensive ground testing required to ensure successful launch and on-orbit operation. This paper describes the sequence and results of the environmental tests performed on an engineering model and all the flight hardware of the GLAST LAT Tracker. Environmental tests include vibration testing, thermal cycles and thermal-vacuum cycles of every tray and tower as well as the verification of their electrical performance.

High efficiency plastic scintillator detector with wavelength-shifting fiber readout for the GLAST Large Area Telescope

This paper describes the design and performance studies of the scintillator tile detectors for the anti-coincidence detector (ACD) of the Large Area Telescope (LAT) on the Gamma ray Large Area Space Telescope (GLAST), scheduled for launch in early 2008. The scintillator tile detectors utilize wavelength-shifting fibers and have dual-photomultiplier-tube readout. The design requires highly efficient and uniform detection of singly charged relativistic particles over the tile area and must meet all requirements for a launch, as well as operation in a space environment. We present here the design of three basic types of tiles used in the ACD, ranging in size from ∼450 to ∼2500 cm 2, all ∼1 cm thick, with different shapes, and with photoelectron yield of ∼20 photoelectrons per minimum ionizing particle at normal tile incidence, uniform over the tile area. Some tiles require flexible clear fiber cables up to 1.5 m long to deliver scintillator light to remotely located photomultiplier tubes.

The GLAST large area telescope: Design, construction, test and calibration

The Gamma-ray Large Area Space Telescope (GLAST) is an international, multi-agency satellite mission with a vast and ambitious physics program in gamma-ray astronomy, particle astrophysics and cosmology. The Large Area Telescope (LAT) is the main instrument onboard GLAST and will detect high energy gamma rays with unprecedented resolution and sensitivity. After successful integration of the three detector subsystems—a silicon-strip tracker-converter, a CsI imaging calorimeter and an outer plastic scintillator serving as anti-coincidence detector—into the telescope, the LAT was installed on the satellite in preparation for the January 2008 launch. Highlights of the LAT instrument performance and of the main technological challenges encountered during the telescope design, commissioning and calibration phases are discussed here, as well as their impact on the mission discovery potential.

GLAST large area telescope multiwavelength planning

Gamma-ray astrophysics depends in many ways on multiwavelength studies. The Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) Collaboration has started multiwavelength planning well before the scheduled 2007 launch of the observatory. Some of the high-priority multiwavelength needs include: (1) availability of contemporaneous radio and X-ray timing of pulsars; (2) expansion of blazar catalogs, including redshift measurements; (3) improved observations of molecular clouds, especially at high galactic latitudes; (4) simultaneous broad-band blazar monitoring; (5) characterization of gamma-ray transients, including gamma ray bursts; (6) radio, optical, X-ray and TeV counterpart searches for reliable and effective sources identification and characterization. Several of these activities are needed to be in place before launch.

The anti-coincidence detector for the GLAST large area telescope

This paper describes the design, fabrication and testing of the Anti-Coincidence Detector (ACD) for the Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT). The ACD is LATs first-level defense against the charged cosmic ray background that outnumbers the gamma rays by 3–5 orders of magnitude. The ACD covers the top and four sides of the LAT tracking detector, requiring a total active area of ∼8.3 m 2. The ACD detector utilizes plastic scintillator tiles with wavelength shifting fiber readout. In order to suppress self-veto by shower particles at high gamma-ray energies, the ACD is segmented into 89 tiles of different sizes. The overall ACD efficiency for detection of singly charged relativistic particles entering the tracking detector from the top or sides of the LAT exceeds the required 0.9997.

GLAST Tracker

The Large Area Telescope (LAT) on board the Gamma-ray Large-Area Space Telescope (GLAST) is a pair-conversion gamma-ray detector designed to explore the gamma-ray universe in the 20 MeV–300 GeV energy band. The Tracker subsystem of the LAT will perform tracking of electron and positrons to determine the origin of the gamma-ray. The design and performance of the GLAST LAT Tracker are described in this paper.

The GLAST large area telescope instrument

The LAT instrument on the Gamma-ray Large Area Space Telescope (GLAST) project is a gamma-ray pair-conversion telescope designed to improve upon the sensitivity of the Compton Gamma-Ray Observatory EGRET instrument by at least a factor of 30. The LAT design is based upon a silicon-strip tracker/converter, a CsI calorimeter, and a plastic-scintillator anticoincidence shield. The project is approaching its critical design review and is scheduled for launch in 2006. This talk gives an overview of the LAT science objectives, the LAT design, and the status of the engineering effort and instrument production plans.