Breaking the rules at z0.45: the rebel case of RBS 1055

A. Marinucci, G. Vietri, E. Piconcelli, S. Bianchi, M. Guainazzi, G. Lanzuisi, D. Stern, C. Vignali

Submitted on 4 September 2022


We report on a long (250 ks) NuSTAR observation of the bright quasar RBS 1055 performed in March 2021, and archival XMM-Newton pointings (185 ks) taken in July 2014. An optical spectrum of the source taken with the Double Spectrograph at the Palomar Observatory, quasi-simultaneous with the NuSTAR observations, is also analyzed. We find that the two-coronae model, in which a warm and hot corona coexist, well reproduces its broad band spectrum, with temperatures kTe=0.120.03+0.08 keV, kTe=3010+40 keV and Thomson optical depths τ=3010+15 and τ=3.01.4+1.0 for the former and the latter component, respectively. We confirm the presence of an intense Fe Kα emission line (EW=55±6 eV) and, when a toroidal model is considered for reproducing the Compton reflection, a Compton-thin solution with NH=(3.20.8+0.9)×1023 cm2 for the circumnuclear reflector is found. The analysis of the optical spectrum reveals a likely peculiar configuration of our line of sight with respect to the nucleus, and the presence of a broad [O III] component, tracing outflows in the NLR, with a velocity shift v=1500±100 km s1, leading to a mass outflow rate M˙out=25.4±1.5 M yr1 and outflow kinetic power E˙kin/LBol 0.33%. We estimate the BH mass to be in the range 2.8×108-1.2×109 M, according to different BLR emission lines, with an average value of <MBH>=6.5×108 M. With an Fe Kα which is 3σ above the value predicted from the EW-L210 keV relation and an extreme source brightness at 2 keV (a factor 10-15 higher than the one expected from the optical/UV), RBS 1055 confirms to be an outlier in the X-rays, compared to other objects in the same luminosity and redshift range.


Comment: 11 pages, 10 figures, 4 tables. Accepted for publication in Astronomy & Astrophysics

Subjects: Astrophysics - High Energy Astrophysical Phenomena; Astrophysics - Astrophysics of Galaxies