We use cookies to ensure that we give you the best experience on our website. You can change your cookie settings at any time. Otherwise, we'll assume you're OK to continue.

Durham University

Department of Physics

Staff profile

Publication details for Prof Chris Done

Jin, C., Done, C. & Ward, M. (2017). Super-Eddington QSO RX J0439.6−5311 – I. Origin of the soft X-ray excess and structure of the inner accretion flow. Monthly Notices of the Royal Astronomical Society 468(3): 3663-3681.

Author(s) from Durham


We report the results from a recent 133 ks XMM–Newton observation of a highly super-Eddington narrow-line Type-1 quasi-stellar object RX J0439.6−5311. This source has one of the steepest active galactic nuclei hard X-ray slopes, in addition to a prominent and smooth soft X-ray excess. Strong variations are found throughout the 0.3–10 keV energy range on all time-scales covered by the observation, with the soft excess mainly showing low-frequency (LF) variations below 0.1 mHz while the hard X-rays show stronger variability at higher frequencies. We perform a full set of spectral-timing analysis on the X-ray data, including a simultaneous modelling of the time-averaged spectra, frequency-dependent root-mean-square and covariance spectra, lag-frequency and lag-energy spectra. Especially, we find a significant time-lag signal in the LF band, which indicates that the soft X-rays lead the hard by ∼4 ks, with a broad continuum-like profile in the lag spectrum. Our analysis strongly supports the model where the soft X-ray excess is dominated by a separate low temperature, optically thick Comptonization component rather than relativistic reflection or a jet. This soft X-ray emitting region is several tens or hundreds of Rg away from the hot corona emitting hard X-rays, and is probably associated with a geometrically thick (‘puffed-up’) inner disc region.