Origin of the X-ray Emission in the Nuclei of FR Is

TL;DR

This study analyzes the origin of X-ray emissions in FR I galaxy nuclei, revealing that low-luminosity sources are jet-dominated, supporting models predicting a shift from accretion flow to jet dominance at low luminosities.

Contribution

It provides multi-waveband spectral analysis of eight FR I sources, confirming the transition from ADAF to jet dominance in X-ray emission at low luminosities.

Findings

X-ray emission in high L_X source from ADAF

X-ray emission in low L_X sources dominated by jets

Accretion rates exceed Bondi estimates, indicating additional fuel sources

Abstract

We investigate the X-ray origin in FRIs using the multi-waveband high resolution data of eight FR I sources, which have very low Eddington ratios. We fit their multi-waveband spectrum using a coupled accretion-jet model. We find that X-ray emission in the source with the highest L_X (~1.8*10^-4 L_Edd) is from the advection-dominated accretion flow (ADAF). Four sources with moderate L_X(~several*10^-6 L_Edd) are complicated. The X-ray emission of one FR I is from the jet, and the other three is from the sum of the jet and ADAF. The X-ray emission in the three least luminous sources (L_X<1.0*10^-6L_Edd) is dominated by the jet. These results roughly support the predictions of Yuan and Cui(2005) where they predict that when the X-ray luminosity of the system is below a critical value, the X-radiation will not be dominated by the emission from the ADAF any longer, but by the jet. We also find that the accretion rates in four sources must be higher than the Bondi rates, which implies that other fuel supply (e.g., stellar winds) inside the Bondi radius should be important.