X-Ray Observations of PKS 0558-504: a Test of Models for Narrow-Line Seyfert 1 Galaxies

Recent ROSAT observations of narrow-line Seyfert 1 galaxies find a very steep soft spectrum and rapid variability. It has been suggested that these properties result from an extreme value of a yet unknown physical parameter; a high accretion rate, low black hole mass or face-on orientation have been suggested. During a Ginga observation of bright NLS1 PKS 0558-504, a flare was observed rise time so rapid for this luminous object that the emission must be beamed. If reconfirmed, this behavior would support the face-on orientation model. PKS 0558-504 is one of the few NLS1s known to be bright enough above 10 keV that good spectral constraints on the reflection component, common in broad-line Seyfert 1s, is possible. We propose a 60ks RXTE observation; if a SAX priority