Mon. Not. R. Astron. Soc., 408, 551-564 (2010/October-2)
Evidence for a truncated accretion disc in the low-luminosity Seyfert galaxy, NGC 7213 ?
LOBBAN A.P., REEVES J.N., PORQUET D., BRAITO V., MARKOWITZ A., MILLER L. and TURNER T.J.
Abstract (from CDS):
We present the broad-band 0.6-150keV Suzaku and Swift BAT spectra of the low-luminosity Seyfert galaxy, NGC 7213. The time-averaged continuum emission is well fitted by a single power law of photon index Γ = 1.75, and from consideration of the Fermi flux limit we constrain the high-energy cut-off to be 350keV < Ecut< 25MeV. Line emission from both near-neutral iron Kα at 6.39keV and highly ionized iron, from Fexxv and Fexxvi, is strongly detected in the Suzaku spectrum, further confirming the results of previous observations with Chandra and XMM-Newton. We find the centroid energies for the emission from Fexxv and Fexxvi to be 6.60 and 6.95keV respectively, with the latter appearing to be resolved in the Suzaku spectrum. From modelling, we show that the Fexxv and Fexxvi emission can result from a highly photoionized plasma, with a column density of NH∼ 3x1023/cm2. A Compton reflection component, e.g. originating from an optically thick accretion disc or a Compton-thick torus, appears either very weak or absent in this active galactic nucleus (AGN), subtending <1sr to the X-ray source, consistent with previous findings. Indeed, the absence of Compton reflection from either neutral or ionized material coupled with the lack of any relativistic Fe K signatures in the spectrum suggests that an inner, optically thick accretion disc is absent in this source. Instead, the accretion disc could be truncated with the inner regions perhaps replaced by a Compton-thin radiatively inefficient accretion flow (RIAF). Thus, the Fexxv and Fexxvi emission could both originate in ionized material perhaps at the transition region between the hot, inner flow and the cold, truncated accretion disc on the order of 103-104 gravitational radii from the black hole. The origin for the unresolved neutral FeKα emission is then likely to be further out, perhaps originating in the optical broad-line region or a Compton-thin pc-scale torus.
© 2010 The Authors. Journal compilation © 2010 RAS
accretion, accretion discs - atomic processes - galaxies: active - galaxies: Seyfert - X-rays: galaxies
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