Balloon flight experiment for GLAST

GLAST (Gamma-ray Large Area Telescope, Figure 1) is a gamma-ray satellite that will be launched early in the New Century, 2005. GLAST is expected to show sensitivity 50-100 times higher than that of the previous gamma-ray satellite (Figure 2).A main detector of GLAST is a LAT (Large Area Telescope), consists of a pair-conversion type gamma-ray Tracker using Silicon Strip Detector, Calorimeter made of arrayed CsI crystals, and Anti-Coincidence Detector (ACD) made of plastic scintillator.

Uno S., Mizuno T. (Hiroshima Univ.), Kamae T. (Hiroshima Univ./ SLAC), Hirano K., Mizushima H., Ogata S., Ohsugi T., Fukazawa Y.(Hiroshima Univ.), Ozaki M. (ISAS), Thompson D., Ormes J. (NASA/GSFC), Johnson N., Lovellette M.(NRA), Godfrey G., Russel JJ. (SLAC), Williams S., Lauben D. (Stanford Univ.), Johnson R.(UCSC), and other GLAST balloon team.

GLAST (Gamma-ray Large Area Telescope) Balloon Flight for GLAST

Figure 1.Schematic overview of GLAST. LAT consists of 4*4=16 modules called Tower.

Figure 2The number of Detected objects for previous and future high-energy astronomical satellites. GLAST is expected to observe more than thousands gamma-ray objects.

In order to validate the GLAST in a single-tower level, a balloon experiment is planned in this June at Palestine, Texas. Major objectives are to examine its ability to deal with gamma-ray events and to reject backgrounds. Most of the instruments are based on that used for Beam Test performed SLAC in 1999, whereas some new components (such as External Target, see Figure 5) will be added. Balloon Flight Engineering Model is now under integration at SLAC .

Figure 3A balloon ready to be launched. Instruments are in gondola that is shown in the near side of this picture.

Figure 4BFEM under integration at SLAC, with two graduatestudents from Hiroshima University.

Figure 5Plastic scintillator with photo-multiplier tube called External Target (XGT), a new instruments on board balloon. When cosmic-ray hit the target and generate pi0-meson, it will immediately decayed into gamma-rays. By introducing XGT, we can obtain tagged gamma-ray events.

Figure 6XGT are developed by Japanese GLAST group. Left figure shows its response to cosmic-ray muon and the right one shows the obtained spectrum.

Figure 7A Tracker used for the Beam Test in 1999,developed by UCSC. After being applied applying some modification, it will be used for Balloon Flight.

Figure 8A Calorimeter utilized for BeamTest, developed by NRL. Each layer of CsI crystals is arranged alternatively in two perpendicular directions in order to get the position information.

Figure 8A photo of the Pressure vessel (PV).The whole detectors of Balloon Flight are housed in the PV with a pressure of about 1 atom.

Objective 1 – gamma-ray event from XGT

In order to study the detector response and to estimate the gamma-ray event rate on Balloon, we developed Monte-Carlo simulator based on Geant 4. We also constructed cosmic-ray generator by referring the paper about previous measurements and theoretical predictions (See poster #187). During 8-hours flight, we will obtain about 500 tagged gamma-ray events generated at targets.

Figure 9A show-case event where pi-0 decayed gamma-ray generated at target is converted at Tracker and deposited most of its energy in calorimeter.

Objective 2– Background on balloon.

A Balloon Flight for GLAST also intend to measure background spectrum in high altitude, and to validate the detector’s ability to reject them. With cosmic-ray generators (poster #187) and detector simulator, we study the background.

Figure 10A sample of the background expected on balloon flight. A cosmic-ray electron hit the pressure vessel and gamma-ray generated via bremsstrahlung hit the tracker.

External Target (XGT)

Tracker Calorimeter

Pressure Vessel