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Several Active Galactic Nuclei (AGNs) have been reported to harbor fast outflows exceeding 10,000 km?s?1, which are detected mostly in their low-resolution CCD X-ray spectra. Only few, however, were detected with high-resolution grating spectrometers. Most of the grating detected outflows have been observed multiple times. In these cases, the absorption spectrum changes are indicating that variability is common among these high-velocity winds. In this paper we revisit the grating observations of PG?1211+143, and PDS?456, and report preliminary results on 4C?74.26. We discuss the spectral variability of the first two sources and its implications to the outflows. 相似文献
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Patrick Cohendet Ehud Zuscovitch 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(7):23-31
La technologie spatiale s'est progressivement révélée comme un centre de propulsion technologique et économique pour les pays industriels qui ont pris partie dans l'effort de financement du programme spatial. La question que nous devons nous poser est de savoir dans quelle mesure le savoir et l'expérience accumulés lors du processus de production de cette technologie peut servir d'exemple à la forme de propagation du progrès économique pour les pays en voie de développement. 相似文献
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