Towards an informed quest for accretion disc winds in quasars: the intriguing case of Ton 28

Abstract

We report on the detection of a blueshifted Fe K absorption feature in two consecutive XMM-Newton observations of the luminous blue quasar Ton 28, at the 4$\sigma$ cumulative significance. The rest energy of 9.2 keV implies the presence of an accretion disc wind with bulk outflow velocity of $\sim$0.28$c$, while the kinetic power is most likely a few per cent of the quasar luminosity. Remarkably, Ton 28 had been specifically selected as an optimal target to reveal an ultra-fast X-ray wind based on its total luminosity ($L_{\mathrm{bol}}>10^{46}$ erg s${}^{-1}$) and [OIII] $\lambda$5007Å equivalent width (EW < 6 Å), suggestive of high accretion rate and low inclination, respectively. Other peculiar optical/UV emission-line properties include narrow H$\beta$, strong FeII and blueshifted CIV. These are key parameters in the Eigenvector 1 formalism, and are frequently found in active galaxies with ongoing accretion disc winds, hinting at a common physical explanation. Provided that the effectiveness of our selection method is confirmed with similar sources, this result could represent the first step towards the characterization of black-hole winds through multiwavelength indicators in the absence of high-quality X-ray spectra.

Accepted for publication in MNRAS Letters (4 figures, 2 tables)