Instruments Compton Gamma Ray Observatory

1 instruments

1.1 batse
1.2 osse
1.3 comptel
1.4 egret

instruments

cgro carried complement of 4 instruments covered unprecedented 6 decades of electromagnetic spectrum, 20 kev 30 gev (from 0.02 mev 30000 mev). in order of increasing spectral energy coverage:

batse

the burst , transient source experiment, (batse) nasa s marshall space flight center searched sky gamma ray bursts (20 >600 kev) , conducted full sky surveys long-lived sources. consisted of 8 identical detector modules, 1 @ each of satellite s corners (left, right; front , back; top , bottom). each module consisted of both nai(tl) large area detector (lad) covering 20 kev ~2 mev range, 50.48 cm in dia 1.27 cm thick, , 12.7 cm dia 7.62 cm thick nai spectroscopy detector, extended upper energy range 8 mev, surrounded plastic scintillator in active anti-coincidence veto large background rates due cosmic rays , trapped radiation. sudden increases in lad rates triggered high-speed data storage mode, details of burst being read out telemetry later. bursts typically detected @ rates of 1 per day on 9-year cgro mission. strong burst result in observation of many thousands of gamma rays within time interval ranging ~0.1 s 100 s.

osse

the oriented scintillation spectrometer experiment, (osse), naval research laboratory detected gamma rays entering field of view of of 4 detector modules, pointed individually, , effective in 0.05 10 mev range. each detector had central scintillation spectrometer crystal of nai(tl) 12 in (303 mm) in diameter, 4 in (102 mm) thick, optically coupled @ rear 3 in (76.2 mm) thick csi(na) crystal of similar diameter, viewed 7 photomultiplier tubes, operated phoswich: i.e., particle , gamma-ray events rear produced slow-rise time (~1 μs) pulses, electronically distinguished pure nai events front, produced faster (~0.25 μs) pulses. csi backing crystal acted active anticoincidence shield, vetoing events rear. further barrel-shaped csi shield, in electronic anticoincidence, surrounded central detector on sides , provided coarse collimation, rejecting gamma rays , charged particles sides or of forward field-of-view (fov). finer level of angular collimation provided tungsten slat collimator grid within outer csi barrel, collimated response 3.8° x 11.4° fwhm rectangular fov. plastic scintillator across front of each module vetoed charged particles entering front. 4 detectors typically operated in pairs of two. during gamma-ray source observation, 1 detector take observations of source, while other slew off source measure background levels. 2 detectors routinely switch roles, allowing more accurate measurements of both source , background. instruments slew speed of approximately 2 degrees per second.

comptel

the imaging compton telescope, (comptel) max planck institute extraterrestrial physics, university of new hampshire, netherlands institute space research, , esa s astrophysics division tuned 0.75-30 mev energy range , determined angle of arrival of photons within degree , energy within 5 percent @ higher energies. instrument had field of view of 1 steradian. cosmic gamma-ray events, experiment required 2 simultaneous interactions, in set of front , rear scintillators. gamma rays compton scatter in forward detector module, interaction energy e1, given recoil electron measured, while compton scattered photon caught in 1 of second layer of scintillators rear, total energy, e2, measured. these 2 energies, e1 , e2, compton scattering angle, angle θ, can determined, along total energy, e1 + e2, of incident photon. positions of interactions, in both front , rear scintillators, measured. vector, v, connecting 2 interaction points determined direction sky, , angle θ direction, defined cone v on source of photon must lie, , corresponding event circle on sky. because of requirement near coincidence between 2 interactions, correct delay of few nanoseconds, modes of background production suppressed. collection of many event energies , event circles, map of positions of sources, along photon fluxes , spectra, determined.

egret



the energetic gamma ray experiment telescope, (egret) measured high energy (20 mev 30 gev) gamma ray source positions fraction of degree , photon energy within 15 percent. egret developed nasa goddard space flight center, max planck institute extraterrestrial physics, , stanford university. detector operated on principle of electron-positron pair production high energy photons interacting in detector. tracks of high-energy electron , positron created measured within detector volume, , axis of v of 2 emerging particles projected sky. finally, total energy measured in large calorimeter scintillation detector @ rear of instrument.