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Astron. Astrophys. 355, 121-127 (2000)

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A hard medium survey with ASCA

III. a Type 2 AGN revealed from X-ray spectroscopy *

R. Della Ceca 1, T. Maccacaro 1, P. Rosati 2 and V. Braito 1

1 Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy
2 European Southern Observatory, 85748 Garching bei München, Germany

Received 12 November 1999 / Accepted 17 December 1999


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 - AXJ2254+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 AXJ2254+1146 is best described by a model consisting of an unresolved Gaussian line at [FORMULA] keV plus the so called "leaky-absorber" continua having an intrinsic power law photon index of [FORMULA] = [FORMULA] (1 [FORMULA] confidence interval). The best fit values of the absorbing column density ([FORMULA] = [FORMULA] cm-2), of the line equivalent width ([FORMULA] keV) and of the scattering fraction ([FORMULA]), 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 ([FORMULA]) that, even on positional ground considerations alone, is the most likely optical counterpart of AXJ2254+1146. Subsequent optical spectroscopy of UGC 12237 has confirmed its Seyfert 2 optical nature.

Key words: X-rays: galaxies – galaxies: Seyfert – cosmology: observations

* Based on observations performed at the European Southern Observatory, Paranal, Chile

© European Southern Observatory (ESO) 2000

Online publication: March 17, 2000