International Gamma-Ray Astrophysics Laboratory

The INTErnational Gamma-Ray Astrophysics Laboratory (shortened INTEGRAL ) is a satellite European Astrophysique for the study of the gamma rays. To date (at the end of 2007), INTEGRAL is always in function.

Mission and orbit

The Gamma rays and the X-rays cannot penetrate in the atmosphere Ground stre. The direct observations such rays can thus be done only since space. INTEGRAL was launched from the space center of Baïkonour, with the Kazakhstan, the October 17th 2002, by a Russian rocket Proton on an elliptic orbit very , with one sidereal period of 3 Jour S . The Orbite of INTEGRAL was selected so that the satellite passes the maximum of time apart from the Ceinture of radiations around the Earth. The satellite is controlled since ESOC, with Darmstadt, in Germany, thanks to two antenna S located in Belgium and California (the United States of America). The consumption of the Carburant of INTEGRAL follows the predictions, and the satellite already exceeded its 2,2 years life time envisaged. It should continue to operate until the December 31st 2012.

Instruments

The 4 instruments on board INTEGRAL are coalignés to be able to observe the same field at the same time. The 3 instruments of high energy use the technique of the Masque coded, since there do not exist Miroir S which allow the focusing of the x-rays and of the Gamma rays. These coded masks were mainly developed by the Université of Valence, in Spain.

The imagor of INTEGRAL is called IBIS ( Imager one Board the INTEGRAL Satellite ). He can observe between 15 keV and 10 MeV. Its space resolution is 12 minutes of arc, but the Déconvolution can reduce it to a much better value, reaching a Minute of arc. A mask of 95 by 95 rectangular tiles of Tungstène is located at 3,2 Mètre S above the detectors. The system of detectors of IBIS contains a foreground of 128 by 128 tiles of Tellurure of cadmium (called INTEGRAL ISGRI for Software Gamma-Ray To color ), then a second plan of 64 by 64 tiles of Iodure of cesium ( PICsIT , for Pixellated Cesium-Iodid Telescopes ). ISGRI is sensitive until approximately 500 KeV, while PICSIT extends up to 10 MeV. The two instruments are surrounded by protective screens in Tungstène and Plomb.

The primary Spectromètre on board INTEGRAL is called SPI ( INTEGRAL SPectrometer for ). It observes between 20 keV and 8 MeV. SPI also consists of a mask coded of tiles hexagonal S of Tungstène, with the top of a made detector of 19 crystals of Germanium. These crystals are cooled actively by a mechanical system, and give a resolution in energy between 2 keV and 1MeV.

IBIS and SPI needs a method to stop ambient radiation (like the cosmic rays. This method consists in using a plastic mask scintillating of located behind the tungsten tiles. This mask absorbs the secondary radiation produced by the impacts on tungsten. This mask is supplemented by a scintillating screen of Germanate of bismuth, is located around and on the back of SPI . This system is called ACS ( AntiCoincidence Shield ). The enormous surface of the ACS in fact almost an instrument with him all alone. Since it is sensitive to the rays coming from all the directions in the sky, it is a detector of natural Gamma rays. Recently, of new algorithms allowed to use the ACS like a Télescope, thanks to the phenomenon of double Diffusion Compton. Thus, the ACS can be used “to observe” objects apart from the field of sight of the satellite.

INTEGRAL has moreover two instruments for the x-rays known as “soft”, between 3 and 35 keV. These two instruments, called JEM-X are identical, and increase the field of Wavelength covered by the satellite. Its space resolution is better than that of IBIS because the smallest wavelengths. Its detectors are Scintillateur S gas with the Xénon and Méthane.

Finally, INTEGRAL has also an optical camera: OMC ( Optical Monitor Camera ), sensitive to the wavelengths of the visible field and Ultraviolet. It is mainly an instrument of support.

The satellite has also a monitor of radiation, called IREM ( INTEGRAL Radiation Environment Monitor ), to monitor the orbital basic level, and is also useful for the calibration of the data. IREM is sensitive to the electron S and the Proton S present in the Ceinture of radiation Ground stre, like with the cosmic rays. If the basic level is too high, IREM can extinguish the scientific instruments, in order to protect them.

See too

Internal bonds

References

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