2004A&A...418..907G

We report the discovery of a Narrow Line QSO located at about 1.3' from the Broad Line Radio Galaxy 3C 445. The source, 1WGA J2223.7-0206, although already revealed by ROSAT, has never been optically identified previously. An XMM-Newton observation of 3C 445 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 0.2-10keV spectrum is well represented by a power law (Γ=2.5) plus a black body component (kT=117eV) absorbed by Galactic N_H. About 80% of the X-ray flux (F_0.2–10keV∼3x10^–13erg/cm/s) is emitted below 2keV. The 0.2-2keV flux is observed to decrease by about a factor 1.6 in about 5000s. 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 H_β and the flux ratio [O III]/H_β are 2000km/s and 0.21, respectively. The optical luminosity (M_R=-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 (L_bol≥3x10⁴⁵erg/s) implying, for accretion rates close to the Eddington limit, a black hole mass M_BH≥2x10⁷M_☉.