ASCA and ROSAT observations of NGC 5548: discrepant spectral indices |
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| Authors: | K Iwasawa A C Fabian K Nandra |
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| Institution: | Institute of Astronomy, Madingley Road, Cambridge CB3 0HA; NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA |
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| Abstract: | We report on simultaneous ASCA and ROSAT observations of the Seyfert galaxy NGC 5548 made during the ASCA Performance Verification phase. Spectral features due to a warm absorber and reflection are clearly seen in the X-ray spectra. We find that the continuum spectral shape differs between the ASCA and ROSAT data sets. The photon-index obtained from the ROSAT PSPC exceeds that from the ASCA SIS ΔΓ≈0.4. The discrepancy is clear even in the 0.5–2 keV energy band over which both detectors are sensitive. The spectra cannot be made consistent by choosing a more complex model. The problem likely lies in the response curve (estimated effective area) of one, or both, detectors. There may be important consequences for a wide range of published results. |
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| Keywords: | galaxies: active galaxies: individual: NGC 5548 galaxies: Seyfert X-rays: galaxies |
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