2000A&A...355..121D

In this paper we report the discovery of a hard X-ray selected Type 2 Seyfert galaxy and we present and discuss its X-ray and optical spectrum together with the radio to X-ray energy distribution. The X-ray source - AX J2254+1146 - is part of the ASCA Hard Serendipitous Survey (HSS). What makes this discovery particularly noteworthy is the fact that the Type 2 classification of this Seyfert galaxy has resulted directly from the X-ray data and has been confirmed by optical spectroscopy only subsequently. The X-ray spectrum of AX J2254+1146 is best described by a model consisting of an unresolved Gaussian line at 6.43±0.1keV plus the so called ``leaky-absorber" continua having an intrinsic power law photon index of Γ=2.51^2.76_2.17 (1σ confidence interval). The best fit values of the absorbing column density (N_H=1.85^2.24_1.47x10²³cm^–2), of the line equivalent width (0.6^0.84_0.36keV) and of the scattering fraction (0.7^1.4_0.1%), lead us to classify it as a Type 2 AGN from an X-ray point of view. Inspection of the POSS II image reveals the presence, within the ASCA X-ray error circle, of the nearby Sbc spiral galaxy UGC 12237 (m_Bo=14.26) that, even on positional ground considerations alone, is the most likely optical counterpart of AX J2254+1146. Subsequent optical spectroscopy of UGC 12237 has confirmed its Seyfert 2 optical nature.