We report the first direct X-ray evidence that an AGN is hidden in the center
of IRAS12393+3520. An ASCA observation of this target unveiled a bright (0.5-10
keV luminosity 3.9 x 10^42 erg/s) and variable source, with minimum observed
doubling/halving time scale comprised in the range 30-75 ks. A model composed
by a simple power-law, with photon index ~1.8 and an absorption edge, whose
threshold energy is consistent with K-shell photoionization of OVII, provides
an adequate fit of the spectrum. This suggests that we are observing the
emission from the nuclear region through a warm absorber of N_H a few
10^{21}/cm/cm. If it has internal dust with Galactic gas-to-dust ratio, it
could explain the lack of broad Hbeta emission, even in the episodic presence
of a broad Halpha emission line. Optical spectra obtained over several years
show indeed variations in the strength of this broad Halpha component. A
distribution of dusty, optically thick matter on spatial scales a few hundreds
parsec, which does not intercept the line of sight towards the nucleus, is
probably required to account simultaneously for the relative [OIII] luminosity
deficit in comparison to the X-rays. The high IR to X-ray luminosity ratio is
most likely due to intense star formation in the circumnuclear region.
IRAS12393+3520 might thus exhibit simultaneously nuclear activity and
remarkable star formation.Comment: 9 Latex pages, 8 figures, Accepted for publication in Astronomy &
Astrophysic
