The ionizing source of the nucleus of NGC 1097

Abstract

We present new observations in X-ray and optical/ultraviolet of the nucleus of NGC 1097 known for the abrupt appearance of broad, double-peaked Balmer lines in its spectrum in 1991. These new observations are used to construct the spectral energy distribution (SED) of the central engine. From the SED we infer that this AGN is radio-loud and has a bolometric luminosity $L_{\rm Bol} \sim 10^{42} \: \textrm{erg s}^{-1}$, implying a low Eddington ratio of $L_{\rm Bol}/L_{\rm Edd} \sim 10^{-4}$. These results suggest that the central ionizing source is an advection-dominated accretion flow (ADAF) in the form of an ellevated structure which photoionizes an outer thin disk. We fit a simplified ADAF model to the SED and obtain limits on the values of the mass accretion rate $\dot{M}$ and accretion efficiency η, namely $\dot{M}/{\dot{M}_{\rm Edd}} \gtrsim 10^{-3}$ and $\eta \lesssim 10^{-2}$. We identify an ‘energy budget’ problem: if the central photoionizing source is isotropic, the covering factor of the line-emitting portion of the thin accretion disk is ≈6, i. e. the central source accounts for only 20% of the energy emitted in the double-peaked Balmer lines.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html