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We investigate the X-ray origin in FR Is using the radio, submillimetre,optical, and {\em Chandra} X-ray data of a small sample consisting of eight FRI sources. These sources are very dim, with X-ray luminosities $L_{\rmX}/L_{\rm Edd} \sim 10^{-4}-10^{-8}$ ($L_{\rm X}$ is the X-ray luminositybetween 2-10 keV). We try to fit the multiwaveband spectrum using a coupledaccretion-jet model. In this model, the accretion flow is described by anadvection-dominated accretion flow (ADAF) while in the innermost region of ADAFa fraction of accretion flow is transferred into the vertical direction andforms a jet. We find that X-ray emission in the source with the highest $L_{\rmX}$ ($\sim 1.8 \times 10^{-4}L_{\rm Edd}$) is from the ADAF. The results forthe four sources with moderate $L_{\rm X}$ ($\sim$ several $\times10^{-6}L_{\rm Edd}$) are complicated. Two are mainly from the ADAFs, one fromthe jet, and the other from the sum of the jet and ADAF. The X-ray emission inthe three least luminous sources ($L_{\rm X} \lesssim 1.0\times 10^{-6}L_{\rmEdd}$) is dominated by the jet although for one source it can also beinterpreted by the ADAF since the quality of X-ray data is low. We concludethat these results roughly support the predictions of Yuan & Cui (2005) wherethey predict that when the X-ray luminosity of the system is below a criticalvalue, the X-radiation will not be dominated by the emission from the ADAF anylonger, but by the jet. We also investigate the fuel supply in these sources.We find that the accretion rates in four sources among the five in which we canhave good constraints to their accretion rates must be higher than the Bondirates. This implies that other fuel supply, such as the gas released by thestellar population inside the Bondi radius, should be important.

On the origin of X-ray emission in some FR Is: ADAF or jet?