Suzaku observation of the LINER NGC4102

• Published in: Astronomy and astrophysics (Berlin) Vol. 527
• Main Authors: GONZALEZ-MARTIN, O, PAPADAKIS, I, O'BRIEN, P, TUELLER, J, WARWICK, R. S, WATSON, M. G, BRAITO, V, MASEGOSA, J, MARQUEZ, I, MATEOS, S, ACOSTA-PULIDO, J. A, MARTINEZ, M. A, EBRERO, J, ESQUEJ, P
• Format: Journal Article
• Language: English
• Published: Les Ulis EDP Sciences 01.03.2011
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; X-ray: galaxies; galaxies: Seyfert; X-ray galaxies; Accretion rate; Variability; Spectral energy distribution; Cosmic x-ray sources; Luminosity; Emission line galaxies; Supermassive black hole; galaxies: individual: NGC 4102; Continuum; Seyfert galaxies; Near infrared spectrum; galaxies: active; Active galaxy nuclei; Classification; Galaxy nuclei; Emission line; galaxies: nuclei; Accretion; X-ray spectra; Spectral analysis; Active galaxies; Ionization; Tori; Cosmology; Spectral index; Optical extinction; Neutral line
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201016097

Context. 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. Aims. We investigate the broad band X-ray spectrum of NGC  4102, one of the most luminous LINERs in the Swift/BAT survey. Methods. We studied a 80 ks Suzaku spectrum of NGC  4102, together with archival Chandra and Swift/BAT observations. We also studied the optical (3.5 m/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. Results. There is strong evidence that NGC  4102 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 sub(XXV) emission lines in the Suzaku spectrum of the source. NGC  4102 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. Conclusions. All the signatures described in this paper strongly suggest that NGC  4102 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 2 pc away from the nuclear source, inside the torus and perpendicular to the disc. The bolometric luminosity (L sub(bol) = 1.4 × 10 super(43) erg s super(-1)) and accretion rate (ṁ sub(Edd) = 5.4 × 10 super(-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.