XMM-NEWTON OBSERVATIONS OF LUMINOUS NARROW-LINE SEYFERT 1 GALAXIES

摘要

We present results from the XMM-Newton observations of four optically-luminous narrow-line Seyfert 1 galaxies. The obtained X-ray spectra showed that intrinsic absorption is unlikely to be present; all the four X-ray spectra are steep, as is typical among narrow-line Seyferts. Utilizing simultaneous UV observations by the OM, we also investigate the spectral energy distributions in the UV-X-ray band. One object (RX J1225.7+2055) of the four was found to be X-ray weak (the spectral energy index between 2500A and 2keV: α{sub}(ox)～2.0) during our observations. Compiling values of α{sub}(ox) from a larger sample of narrow-line Seyferts, we find that, although the sample is small, the α{sub}(ox) distribution suggests that X-ray weakness may occur more frequently among more luminous objects. This suggest that X-ray weakness may be caused by high accretion rate. We try to interpret the α{sub}(ox) dependence on the optical luminosity, based on simple disk models of an accretion disk sandwiched by coronae.