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(abridged) The radio-quiet quasar PG1416-129 (z=0.129) exhibits atypicaloptical and X-ray properties. Between 1990 and 2000, in response to its opticalcontinuum decrease, the ``classical'' broad component of Hbeta almostcompletely disappeared, with a factor of 10 decrease in the line flux. In theX-ray band, this object was observed by Ginga in 1988 to have the hardestquasar photon index, with Gamma=1.1+/-0.1. We present an XMM/EPIC observationof PG1416-129 performed in July 2004. We analyze the time-averaged pn spectrumof this quasar, as well as perform time-resolved spectroscopy. We find thatduring the present XMM observation, PG1416-129 still has a rather hard photonindex, both in the soft and hard energy ranges, compared to radio-quiet quasarsbut compatible with the photon index value found for radio-loud quasars. Thisobject also shows long-term luminosity variability over 16 years by a factor ofthree with a variation of photon index from ~1.2 to ~1.8. In the soft energyband (0.2-2keV), we found a very weak soft X-ray excess compared to other RQquasars. The whole time averaged spectrum is fit very well either by X-rayionized reflection from the accretion disk surface, by a warm absorber-emitterplus power-law, or by a smeared absorption/emission from a relativisticoutflow. While no constant narrow FeK line at 6.4keV is observed, we find thepossible presence of two non-simultaneous transient iron lines: a redshiftednarrow iron line at about 5.5keV (96.4% confidence level according tomulti-trial Monte-Carlo simulations) at the beginning of this observation andthe appearance of a line at 6.3-6.4keV (99.1% c.l.) at the end of theobservation. These variable lines could be generated by discrete hot-spots onthe accretion disk surface.

An XMM-Newton view of the X-ray flat radio-quiet quasar PG 1416-129