1WGA J2223.7-0206: a Narrow–Line Quasi–Stellar Object in the XMM-Newton field of view of 3C445⋆

We report the discovery of a Narrow Line QSO located at about 1.3 from the Broad Line Radio Galaxy 3C445. The source, 1WGA J2223.7-0206 , although already revealed by ROSAT, has never been optically identified previously. An XMM-Newton observation of 3C445 has allowed, for the first time, an accurate X-ray spectral study of 1WGA J2223.7-0206 , revealing an ultra-soft spectrum and fast flux variations typical of Narrow Line AGN. The 0.2-10 keV spectrum is well represented by a power law (Γ = 2.5) plus a black body component (kT = 117 eV) absorbed by Galactic NH . About 80% of the X-ray flux (F0.2−10 keV ∼ 3× 10 −13 erg cm s) is emitted below 2 keV. The 0.2− 2 keV flux is observed to decrease by about a factor 1.6 in about 5000 s. The optical observations, triggered by the X-ray study, confirm the Narrow Line AGN nature of this source. The continuum is blue with typical AGN emission lines, pointing to a redshift z = 0.46. The full width half maximum of Hβ is 2000 km s −1 and the flux ratio [O iii]/Hβ = 0.21. The optical luminosity (MR = −23.2) and the point-like appearance in the optical images identify 1WGA J2223.7-0206 as a Narrow Line QSO. From the optical–UV–X–ray Spectral Energy Distribution we obtain a lower limit of the bolometric luminosity of 1WGA J2223.7-0206 (Lbol ≥ 3× 10 45 erg s) implying, for accretion rates close to the Eddington limit, a black hole mass MBH ≥ 2.4× 10 7 M⊙.