XMM-Newton monitoring of X-ray variability in the quasar PKS 0558-504

We present the temporal analysis of X-ray observations of the radio-loud Na rrow-Line Seyfert 1 galaxy (NLS1) PKS 0558-504 obtained during the XMM-Newt on Calibration and Performance Verification (Cal/PV) phase. The long term l ight curve is characterized by persistent variability with a clear tendency for the X-ray continuum to harden when the count rate increases. Another s trong correlation on long time scales has been found between the variabilit y in the hard band and the total flux. On shorter time scales the most rele vant result is the presence of smooth modulations, with characteristic time of similar to2 hours observed in each individual observation. The short te rm spectral variability turns out to be rather complex but can be described by a well defined pattern in the hardness ratio-count rate plane.