Does the X-ray emission of the luminous quasar RBS 1124 originate in a mildly relativistic outflowing corona?

TL;DR

This study analyzes Suzaku X-ray observations of the luminous quasar RBS 1124, revealing a rapidly spinning black hole with a mildly relativistic outflowing corona that explains its spectral features and low reflection fraction.

Contribution

It provides evidence that the X-ray corona in RBS 1124 is outflowing at mildly relativistic speeds, affecting the observed reflection and luminosity, which is a novel interpretation for this quasar.

Findings

Detection of a broad iron line and soft X-ray excess.

Black hole spin inferred to be high (a >= 0.6).

Corona likely outflowing at mildly relativistic speeds.

Abstract

We have observed the luminous (L_x ~ 6x10^44 erg/s) radio-quiet quasar RBS 1124 (z=0.208) with Suzaku. We report the detection of a moderately broad iron (Fe) line and of a weak soft X-ray excess. The X-ray data are very well described by a simple model comprising a power law X-ray continuum plus its reflection off the accretion disc. If the inner disc radius we measure (<=3.8 gravitational radii) is identified with the innermost stable circular orbit of the black hole spacetime, we infer that the black hole powering RBS 1124 is rotating rapidly with spin a>= 0.6. The soft excess contribution in the 0.5-2 keV band is ~15%, about half than that typically observed in unobscured Seyfert 1 galaxies and quasars, in line with the low disc reflection fraction we measure (R_disc ~0.4). The low reflection fraction cannot be driven by disc truncation which is at odds not only with the small inner disc radius we infer but, most importantly, with the radiatively efficient nature of the source (L_Bol / L_Edd ~1). A plausible explanation is that the X-ray corona is the base of a failed jet (RBS 1124 being radio-quiet) and actually outflowing at mildly relativistic speeds. Aberration reduces the irradiation of the disc, thus forcing a lower than standard reflection fraction, and halves the inferred source intrinsic luminosity, reducing the derived Eddington ratio from ~1to ~0.5. [abridged]