Investigation of X-ray Objects with Astro-D and ROSAT

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ASCA (ASTRO-D), the fourth X-ray astonomy satellite of ISAS,Japan, was launched in February, 1993. ASCA is an X-ray astronomy observatory which is, for the first time, capable of performing imaging and spectroscopic observations simultaneously over a wide energy range 0.5-10 keV.Whereas, ROSAT,the X-ray astronomy satellite of the Max-Planck Institute, Germany, was launched in June, 1990. ROSAT is also an X-ray astronomy observatory which is characterized by its excellent imaging capability, although it is limited to narrower energy bands than ASCA.ASCA has much higher spectral capability than ROSAT,while ROSAT has much finer imaging capability and higher source detection sensitivity that ASCA.Both observatories are really complimetary to each other.An extensive collaboration between Japanese and German scientists has been carried out in performing simultaneous observations, cross-calibrations of the X-ray telescopes, exchanging the data, developping analysis software, discussing the sc … More ientific yields, presenting the results to international communities, future development of instruments and so on.The ASCA instruments cover the most important energy band for plasma diagnostics, because all the K-lines and the K-absorption edges from oxygen through iron at various ionization stages lie within this band. The CCD camera of ASCA can resolve all major lines individually. Motion of plasma of the order or greater than 1000 km/s can be measured significantly from Doppler shift of the line energies. These capabilities of ASCA allow diagnostics of accreting matter around such compact objeots as neutron stars and black holes. On the other hand, the ROSAT telescope provides an accurate position of each X-ray sources and enables us to indentify the X-ray sources with optically known sources. The highly resolved spatial information with ROSAT also provides powerful means for the investigations of extended plasmas in supernova remnants, galaxies, and clusters of galaxies. Combining these characteristics of the two observatories, several remarkable scientific results have already been obtained and shown in many scientific papers. This collaborative study should be kept continuing in future. Less