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Eklenme Tarihi: 18-11-08
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Dosya Açıklaması : X-ray astronomy is a relatively new field because earth s atmosphere is opaque to X-rays. The serious studies in this field really began in 1960 s. Until this time the sun was the first and only celestial object which was an intense source in X-ray waveband. Because of earths atmosphere absorbs most of the rays in this waveband, it was needed to examine them above the atmosphere and in the first rocket flight the first extrasolar X-ray source Sco x-1 was detected. After that discovery, the first satellite, Uhuru, which was dedicated to X-ray astronomy was launched. It used two beryllium-window proportional counters with mechanical collimators to map the X-ray sky between 2 and 6 keV as the satellite rotated.[4] Uhuru had a time resolution of 0.1 s and was used to discover the Doppler shifts in the pulse period of Cen X-3 that revealed it as a binary system. The Einstein observatory was launched November 1978. It was the first X-ray satellite to provide high-resolution imaging with a grazing-incidence mirror. The European X-Ray Observatory Satellite (EXOSAT) had a 90 hour orbital period which allowed continuous observations of X-ray sources lasting several days without the interference of earth occultations. EXOSAT led to the discovery of quasi-periodic oscillations in the light curves of X-ray binaries. EXOSATs ability to perform long, uninterrupted observations enabled the nature of X-ray bursts to be determined. The third Japanese X-ray satellite Ginga had a large effective area above 10 keV which led to the discovery of cyclotron lines in the spectra of seven X-ray binaries, compared to the two cyclotron line sources that were known previously. ROSAT provided high-resolution imaging and a deep all-sky survey in soft X-rays below 2 keV. NASA Advanced X-ray Astrophysics Facility AXAF is another long- duration orbiting observatory that was scheduled to became operational in 1999.[5] Starting with the Sun as the only celestial source of X-ray, today we know that there are many kinds of X-ray sources in the universe. As being discussed in more detail in the later parts of the report it is known that Rotation-powered pulsars can emit X-rays through synchrotron radiation. Supernova remnants emit X-rays from shocks as ejecta collide with and sweep up the interstellar medium. The the hot coronae of stars emit soft X-rays. However, the accretion of matter onto compact objects is the driving force behind X-ray binaries and active galactic nuclei, which are among the most luminous sources. Thermal emission from gravitationally bound, hot intracluster gas makes galaxy clusters X-ray emitters. Normal galaxies emit X-rays due to a hot interstellar medium, X-ray binaries, and supernova ...