Friday, 20 April 2007

Data Analysis and Archive for CGRO

The Compton Gamma Ray Observatory (CGRO) was a space observatory detecting light from 20 KeV to 30 GeV in Earth orbit from 1991 to 2000. It featured four main telescopes in one spacecraft covering x-rays and gamma-rays, including various specialized sub-instruments and detectors. Following 14 years of effort, the observatory was launched on the Space ShuttleAtlantis, mission STS-37, on 5 April 1991 and operated until its deorbit on 4 June 2000. It was deployed in low earth orbit at 450 km (280 mi) to avoid the Van Allen radiation belt. It was the heaviest astrophysical payload ever flown at that time at 17,000 kilograms (37,000 lb).

The CGRO was part of NASA's Great Observatories series, with the Hubble Space Telescope, the Chandra X-ray Observatory, and the Spitzer Space Telescope. It was the second of theNASA "Great Observatories" to be launched to space, following the Hubble Space Telescope. CGRO was named after Dr. Arthur Holly Compton (Washington University in St. Louis), Nobel prize winner, for work involved with gamma ray physics. CGRO was built by TRW (now Northrop Grumman Aerospace Systems) in Redondo Beach, CA. CRGO was an international collaboration and additional contributions came from the European Space Agency and various Universities, as well as the U.S. Naval Research Laboratory,

Data Analysis for CGRO


Wednesday, 18 April 2007

A space observatory The Compton Gamma Ray Observatory (CGRO)

Edited by:
Arip Nurahman
(Teacher and Professional Lecturer)
Guru dan Dosen Profesional

Compton Gamma Ray Observatory
Cartoon CGRO.jpg
General information
NSSDC ID 1991-027B
Organization NASA
Major contractors TRW
Launch date 5 April 1991
Launched from Kennedy Space Center
Launch vehicle Space Shuttle Atlantis STS-37
Mission length 9 years, 2 months
Deorbited 4 June 2000
Mass 17,000 kg (37,000 lb)
Orbit height 450 km (280 mi)
Orbit period 90 min (1.5 h)
Telescope style Scintillation detectors
Wavelength Gamma
Diameter N/A
Collecting area Varies by instrument
Focal length N/A
BATSE all-sky monitor
OSSE pointed detectors
COMPTEL imaging telescope
EGRET wide field telescope
Website NASA Compton Gamma Ray Observatory

Space observatory

A space observatory is any instrument in outer space which is used for observation of distant planets, galaxies, and other outer space objects.A large number of observatories have been launched into orbit, and most of them have greatly enhanced our knowledge of the cosmos.Performing astronomy from the Earth's surface is limited by the filtering and distortion of electromagnetic radiation due to the Earth's atmosphere.

This makes it desirable to place astrononomical observation devices into space.As a telescope orbits the Earth outside the atmosphere it is subject neither to twinkling (distortion due to thermal turbulences of the air) nor to light pollution from artificial light sources on the Earth.

But space-based astronomy is even more important for frequency ranges which are outside of the optic window and the radio window, the only two wavelength ranges of the electromagnetic spectrum that are not severely attenuated by the atmosphere.

For example, X-ray astronomy is nearly impossible when done from the Earth, and has reached its current important stand within astronomy only due to orbiting satellites with X-ray telescopes such as the Chandra observatory or XMM-Newton observatory.

Infrared and ultraviolet are also greatly blocked.

Compton Gamma Ray Observatory

The Compton Gamma Ray Observatory (CGRO) was the second of the NASA "Great Observatories" to be launched to space, following the Hubble Space Telescope.The observatory was launched on the Space Shuttle Atlantis, mission STS-37, on 5 April 1991.It was deployed in low earth orbit at 450 km in order to avoid the Van Allen radiation belt.It was the heaviest astrophysical payload ever flown at that time, at 17000 kg. The CGRO is part of NASA's Great Observatories series, with the Hubble Space Telescope, the Chandra X-ray Observatory, and the Spitzer Space Telescope.

See also


External links

Arip Nurahman

Guru dan Dosen Profesional

Semoga Bermanfaat

Tuesday, 10 April 2007

Compton Gamma Ray Observatory Education

Basic results

  • The EGRET instrument conducted the first all sky survey above 100 MeV. Using four years of data it discovered 271 sources, 170 of which were unidentified.
  • The COMPTEL instrument completed an all sky map of 26Al (a radioactive isotope of aluminum).
  • The OSSE instrument completed the most comprehensive survey of the galactic center, and discovered a possible antimatter "cloud" above the center.
  • The BATSE instrument averaged one gamma ray burst event detection per day for a total of approximately 2700 detections. It definitively showed that the majority of gamma-ray bursts must originate in distant galaxies, not nearby in our own Milky Way, and therefore must be enormously energetic.
  • The discovery of the first four soft gamma ray repeaters; these sources were relatively weak, mostly below 100 keV and had unpredictable periods of activity and inactivity
  • The separation of GRBs into two time profiles: short duration GRBs that last less than 2 seconds, and long duration GRBs that last longer than this.

GRB 990123

Gamma ray burst 990123 (23 January 1999) was one of the brightest bursts recorded at the time, and was the first GRB with an optical afterglow observed during the prompt gamma ray emission (a reverse shock flash). This allowed astronomers to measure a redshift of 1.6 and a distance of 3.2 Gpc (10 Gly). Combining the measured energy of the burst in gamma-rays and the distance, the total emitted energy assuming an isotropic explosion could be deduced and resulted in the direct conversion of approximately two solar masses into energy. This finally convinced the community that GRB afterglows resulted from highly collimated explosions, which strongly reduced the needed energy budget.

Miscellaneous results

Education & Outreach

Sunday, 1 April 2007

Compton Gamma Ray Observatory Instruments

CGRO carried a complement of four instruments that covered an unprecedented six decades of the electromagnetic spectrum, from 20 keV to 30 GeV (from 0.02 MeV to 30000 MeV). In order of increasing spectral energy coverage:


  • The Burst and Transient Source Experiment, (BATSE) by NASA's Marshall Space Flight Center searched the sky for gamma ray bursts (20 to >600 keV) and conducted full sky surveys for long-lived sources. It consisted of eight identical detector modules, one at each of the satellite's corners (left, right; front and back; top and bottom). Each module consisted of both a NaI(Tl) Large Area Detector (LAD) covering the 20 keV to ~2 MeV range, 50.48 cm in dia by 1.27 cm thick, and a 12.7 cm dia by 7.62 cm thick NaI Spectroscopy Detector, which extended the upper energy range to 8 MeV, all surrounded by a plastic scintillator in active anti-coincidence to veto the large background rates due to cosmic rays and trapped radiation. Sudden increases in the LAD rates triggered a high-speed data storage mode, the details of the burst being read out to telemetry later. Bursts were typically detected at rates of roughly one per day over the 9-year CGRO mission. A strong burst could result in the observation of many thousands of gamma rays within a time interval ranging from ~0.1 s up to about 100 s.


  • The Oriented Scintillation Spectrometer Experiment, (OSSE), by the Naval Research Laboratory detected gamma rays entering the field of view of any of four detector modules, which could be pointed individually, and were effective in the 0.05 to 10 MeV range. Each detector had a central scintillation spectrometer crystal of NaI(Tl) 12 in (303 mm) in diameter, by 4 in (102 mm) thick, optically coupled at the rear to a 3 in (76.2 mm) thick CsI(Na) crystal of similar diameter, viewed by seven photomultiplier tubes, operated as a phoswich: i.e., particle and gamma-ray events from the rear produced slow-rise time (~1 μs) pulses, which could be electronically distinguished from pure NaI events from the front, which produced faster (~0.25 μs) pulses. Thus the CsI backing crystal acted as an active anticoncidence shield, vetoing events from the rear. A further barrel-shaped CsI shield, also in electronic anticoincidence, surrounded the central detector on the sides and provided coarse collimation, rejecting gamma rays and charged particles from the sides or most of the forward field-of-view (FOV). A finder level of angular collimation was provided by a tungston slat collimator grid within the outer CsI barrel, which collimated the response to a 3.8° x 11.4° FWHM rectangular FOV. A plastic scintillator across the front of each module vetoed charged particles entering from the front. The four detectors were typically operated in pairs of two. During a gamma-ray source observation, one detector would take observations of the source, while the other would slew slightly off source to measure the background levels. The two detectors would routinely switch roles, allowing for more accurate measurements of both the source and background. The instruments could slew with a speed of approximately 2 degrees per second.


  • The Imaging Compton Telescope, (COMPTEL) by the Max Planck Institute for Extraterrestrial Physics, the University of New HampshireNetherlands Institute for Space Research, and ESA's Astrophysics Division was tuned to the 0.75-30 MeV energy range and determined the angle of arrival of photons to within a degree and the energy to within five percent at higher energies. The instrument had a field of view of one steradian. For cosmic gamma-ray events, the experiment required two nearly simultaneous interactions, in a set of front and rear scintillators. Gamma rays would Compton scatter in a forward detector module, where the interaction energy E1, given to the recoil electron was measured, while the Compton scattered photon would then be caught in one of a second layer of scintillators to the rear, where its total energy, E2, would be measured. From these two energies, E1 and E2, the Compton scattering angle, angle θ, can be determined, along with the total energy, E1 + E2, of the incident photon. The positions of the interactions, in both the front and rear scintillators, was also measured. The vectorV, connecting the two interaction points determined a direction to the sky, and the angle θ about this direction, defined a cone about V on which the source of the photon must lie, and a corresponding "event circle" on the sky. Because of the requirement for a near coincidence between the two interactions, with the correct delay of a few nanoseconds, most modes of background production were strongly suppressed. From the collection of many event energies and event circles, a map of the positions of sources, along with their photon fluxes and spectra, could be determined.


  • The Energetic Gamma Ray Experiment Telescope, (EGRET) measured high energy (20 MeV to 30 GeV) gamma ray source positions to a fraction of a degree and photon energy to within 15 percent. EGRET was developed by NASA Goddard Space Flight Center, the Max Planck Institute for Extraterrestrial Physics, and Stanford University. Its detector operated on the principle of electron-positron pair production from high energy photons interacting in the detector. The tracks of the high-energy electron and positron created were measured within the detector volume,and the axis of the V of the two emerging particles projected to the sky. Finally, their total energy was measured in a large calorimeter scintillation detector at the rear of the instrument.