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

¹ Max-Plank-Institut für Extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany e-mail: dporquet@mpe.mpg.de
² Laboratory for High Energy Astrophysics, Code 662, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
³ Dept. of Physics and Astronomy, Johns Hopkins University, 3400 N.  Charles Street, Baltimore, MD 21218, USA
⁴ Dept. of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁵ Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AW, UK

Received: 15 July 2006
Accepted: 20 November 2006

Abstract

Aims.The radio-quiet quasar PG 1416-129 () exhibits atypical optical and X-ray properties. Between 1990 and 2000, in response to its optical continuum decrease, the “classical” broad component of Hβ almost completely disappeared, with a factor of 10 decrease in the line flux. In addition, the width of the broad component of the Hβ line decreased significantly from 4000 km s^-1 to 1450 km s^-1. In the X-ray band, this object was observed by Ginga in 1988 to have the hardest quasar photon index, with . We present an XMM-Newton/EPIC observation of PG 1416-129 performed in July 2004.

Methods.We analyze the time-averaged pn spectrum of this quasar, as well as perform time-resolved spectroscopy.

Results.We find that during the present XMM-Newton observation, PG 1416-129 still has a rather hard photon index, both in the soft (0.2–2 keV) and hard (2–12 keV) energy ranges, compared to radio-quiet quasars (BLS1 and NLS1) but compatible with the photon index value found for radio-loud quasars. This object also shows long-term luminosity variability over 16 years by a factor of three with a variation of photon index from ~1.2 to ~1.8. In the soft energy band (0.2–2 keV), we found a very weak soft X-ray excess compared to other RQ quasars. The whole time averaged spectrum is fit very well either by X-ray ionized reflection from the accretion disk surface, by a warm absorber-emitter plus power-law, or by a smeared absorption/emission from a relativistic outflow. While no constant narrow Fe K line at 6.4 keV is observed, we find the possible presence of two non-simultaneous transient iron lines: a redshifted narrow iron line at about 5.5 keV (96.4% confidence level according to multi-trial Monte-Carlo simulations) at the beginning of this observation and the appearance of a line at 6.3–6.4 keV (99.1% c.l.) at the end of the observation. These variable lines could be generated by discrete hot-spots on the accretion disk surface.