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
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 keV plus the so called "leaky-absorber" continua having an intrinsic power law photon index of = (1 confidence interval). The best fit values of the absorbing column density ( = cm-2), of the line equivalent width ( keV) and of the scattering fraction (), 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 () 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
© European Southern Observatory (ESO) 2000
Online publication: March 17, 2000