X-ray study of accretion flow in narrow-line Seyfert 1 galaxies

We analyzed 13 narrow-line Seyfert 1 galaxies (NLS1s) observed with XMM-Newton. Their X-ray continua are well parameterized by a combination of a hard power law and thermal emission from a standard Shakura-Sunyaev accretion disk. However, the observed disk temperatures are significantly higher than the prediction from the standard disk, and the temperatures are distributed within an extremely narrow range (0.15-0.22 keV) in spite of the wide range of luminosities (LX = 1041-45 erg s-1). Furthermore, we found an anti-correlation between the disk temperature and luminosity of PKS 0558-504. These results strongly indicate the breakdown of the standard accretion picture in NLS1s. We suggest that a slim disk, which is a stable disk solution under a high mass-accretion rate, could be able to explain the observational results, if the photon trapping effect is properly taken into account.