2011A&A...527A.142G

Low-ionisation, nuclear emission-line region (LINER) nuclei are said to be different from other active galactic nuclei (AGN) due to the presence of complex absorbing structures along the line-of-sight and/or an inefficient mode of accretion onto the supermassive black hole. However, this is still open. We investigate the broad band X-ray spectrum of NGC4102, one of the most luminous LINERs in the Swift/BAT survey. We studied a 80ks Suzaku spectrum of NGC4102, together with archival Chandra and Swift/BAT observations. We also studied the optical (3.5m/TWIN at Calar Alto observatory) and near-infrared (WHT/LIRIS at Observatorio Roque los Muchachos) spectra that were taken at the same time as the Suzaku data. There is strong evidence that NGC4102 is a Compton-thick AGN, as suggested by the Swift/BAT detected intrinsic continuum and the presence of a strong narrow, neutral FeKα emission line. We have also detected ionised Fe_XXV emission lines in the Suzaku spectrum of the source. NGC4102 shows a variable soft excess found at a significantly higher flux state at the time of Suzaku observations when compared to Chandra observations. Finally, a complex structure of absorbers is seen with at least two absorbers besides the Compton-thick one, derived from the X-ray spectral analysis and the optical extinction. All the signatures described in this paper strongly suggest that NGC4102 is a Compton-thick Type-2 AGN from the X-ray point of view. The ``soft excess'', the electron scattered continuum component, and the ionised iron emission line might arise from Compton-thin material photoionised by the AGN. From variability and geometrical arguments, this material should be located somewhere between 0.4 and 2pc away from the nuclear source, inside the torus and perpendicular to the disc. The bolometric luminosity (L_bol=1.4x10⁴³erg/s) and accretion rate ({dot}(m)_Edd=5.4x10^–3) are consistent with other low-luminosity AGN. However, the optical and near infrared spectra correspond to that of a LINER source. We suggest that the LINER classification might be due a different spectral energy distribution according to its steeper spectral index.