Article Dans Une Revue Astronomy & Astrophysics - A&A Année : 2010

X-ray and multiwavelength view of NGC 4278. A LINER-Seyfert connection?

Résumé

Based on UV to X-ray and radio to UV flux ratios, some argue that low ionization emission line regions (LINERs) and low luminosity AGN (LLAGN) are a scaled-down version of their more luminous predecessors Seyfert galaxies. Others, based on the lack of X-ray short (hours) time-scale variability, the non-detection of an iron line at 6.4 keV, and the faint UV emission, suggest the truncation of the classical thin accretion disk in the inner regions of the AGN where a radiatively inefficient accretion flow (RIAF) structure forms. We investigate the LINER-Seyfert connection by studying the unabsorbed, AGN powered, LINER galaxy NGC 4278. We analyzed one XMM-Newton and seven Chandra X-ray observations of NGC 4278 spread over a three year period. We detected a flux increase by a factor of ~3 on a ~3 months time-scale and by a factor of 5 between the faintest and the brightest observation separated by ~3 years. During only the XMM-Newton observation, where the highest flux level is detected, we found a 10% flux increase on a ~1 hour time-scale. A combination of an absorbed power law (N(H)~1020 cm-2, Gamma~2.2) plus a thermal component (kT~0.6 keV) were able to fit the Chandra spectra. The XMM-Newton spectra, where the highest X-ray flux is detected, are well fitted with a single absorbed power-law. No Fe K(alpha) emission line is detected at 6.4 keV. We constructed SEDs based on simultaneous or quasi simultaneous observations and compared them to LINER, radio-loud, and radio-quiet quasar SEDs. We find that at a low X-ray flux the NGC 4278 SED resembles that of typical LINER sources where the radio to X-ray emission can be considered as originating from a jet and/or RIAF, whereas at a high X-ray flux, NGC 4278 SED is more like a low luminosity Seyfert SED. Consequently, NGC 4278 could exhibit both LINER and Seyfert nuclear activity depending on the strength of its X-ray emission
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hal-02333963 , version 1 (17-01-2025)

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G. Younes, D. Porquet, B. Sabra, N. Grosso, J. Reeves, et al.. X-ray and multiwavelength view of NGC 4278. A LINER-Seyfert connection?. Astronomy & Astrophysics - A&A, 2010, 517, pp.A33. ⟨10.1051/0004-6361/201014371⟩. ⟨hal-02333963⟩
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