SOFT VARIABILITY AND REFLECTION FEATURES IN THE X-RAY-SPECTRUM OF THE SEYFERT-GALAXY NGC-5506

Observations of the Seyfert 2 galaxy NGC 5506 obtained by Ginga in 1991 July 6-10, are presented. In addition to an iron emission line around 6.4 keV, soft excess emission below 3 keV and a hard tail-like feature are detected. On one episode on July 9, the spectrum softened, over a 5 hr time scale, to a maximum level after which it returned to the level seen on the other observation days. The softness variability may be described in terms of the partial covering model, while the high-energy feature is best described by a feature representing reflection by cold, dense matter. On July 6 and 10, the covering fraction was approximately 80%, but on July 9 this value declined to a minimum value of approximately 60%. While we do not rule out the presence of ionized matter, the lack of correlation of the spectral softness with the continuum flux rules out models based on photoionization as the softness variability mechanism. It is suggested that this mechanism resides in the inner accretion disk where the dip in the apparent covering fraction is due to instabilities in the accretion flow.