On the Origin of X‐Ray Emission in Some FR I Galaxies: ADAF or Jet?

Abstract

We investigate the origin of X-ray emission in FR I galaxies using radio, submillimeter, optical, and Chandra X-ray data for a small sample of eight FR I sources. These sources are very dim, with X-ray luminosities L X /L Edd $ 10 À4 to 10 À8 (with L X the X-ray luminosity between 2 and 10 keV ). We try to fit the multi-wave-band spectra using a coupled accretion-jet model. In this model, the accretion is described by an advection-dominated accretion flow (ADAF ); in the innermost region of the ADAF, a fraction of the flow is transferred into the vertical direction and forms a jet. We find that X-ray emission in the source with the highest L X ($1.8 ; 10 À4 L Edd ) is from the ADAF. The results for the four sources with moderate L X (several times 10 À6 L Edd ) are complicated. Two are dominated by the ADAF, one by the jet, and the other by the sum of the jet and ADAF. The X-ray emission in the three least luminous sources (L X P 1.0 ; 10 À6 L Edd ) is mainly from the jet, although for one source it can also be interpreted as the ADAF, since the quality of the X-ray data is low. We conclude that these results roughly support the prediction of Yuan & Cui that when the X-ray luminosity of a system is below some critical value, the X-radiation will not be dominated by the emission from the ADAF any longer, but by the jet. We also investigate the fuel supply in these sources. We find that the accretion rate in four of the five sources for which we have good constraints must be higher than the Bondi rate. This implies that another fuel supply, such as gas released by the stellar population inside the Bondi radius, should be important.

Correlation between the photon index and X-ray luminosity of black hole X-ray binaries and active galactic nuclei: observations and interpretation

“…Therefore, when the luminosity is below a critical value L crit , we predict the Xray emission will be dominated by the synchrotron emission from the jet . This prediction has been confirmed for observations of the faint LLAGNs and the quiescent state of BHBs (e.g., Wu, Yuan & Cao 2007;Pellegrini et al 2007;Wrobel et al 2008;Pszota et al 2008;Yuan, Yu & Ho 2009;de Gasperin et al 2011;Younes et al 2012;Xie, Yang & Ma 2014).…”

Exploring the Accretion Model of M87 and 3c 84 With the Faraday Rotation Measure Observations

“…Detailed calculations show that when the 2−10 keV X-ray luminosity is lower than a critical value L X,crit given by log(L X,crit /L Edd ) ≈ −5.36 − 0.17log(M/M ⊙ ), the X-ray emission of the system should be dominated by the jet rather than the ADAF . The prediction is supported by later observations (e.g., Pellegrini et al 2007;Wu et al 2007;Wrobel et al 2008;Yuan et al 2009;de Gasperin et al 2011;Younes et al 2012). The X-ray luminosity of M87 is below this critical value and this is the physical base of the jet-dominated model.…”

Study of LINER sources with broad Hαemission

“…The trapped heat will expand the thin accretion disk into a pressure-supported thick disk with a very low radiative efficiency (see Quataert 2001;Yuan 2007;Narayan & McClintock 2008, for reviews). Such radiatively inefficient accretion flow (RIAF) models successfully explained the SED of a large number of LINER sources (Quataert et al 1999;Gammie et al 1999;Ptak et al 2004;Nemmen et al 2006;Wu et al 2007;Yu et al 2011).…”

“…Through synchrotron and synchrotron self-Compton processes, the jet could contribute to the broad-band emission of these low accreting sources, sometimes even dominating the accretion flow emission. Indeed, what is giving rise to the broad-band spectrum, especially the hard X-ray emission, is a highly debated subject, with some crediting completely the RIAF models, others leaning towards a jet origin (Falcke & Markoff 2000;Yuan et al 2002a,b;Wu et al 2007;Markoff et al 2008).…”