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X-ray binaries in outburst typically show two canonical X-ray spectralstates, i.e. hard and soft states, in which the physical properties of theaccretion flow and of the jet are known to change. Recently, the JED-SADparadigm has been proposed for black hole X-ray binaries, aimed to address theaccretion-ejection interplay in these systems. According to this model, theaccretion flow is composed by an outer standard Shakura-Sunyaev disk (SAD) andan inner hot Jet Emitting Disk (JED). The JED produces both the hard X-rayemission, effectively playing the role of the hot corona, and the radio jets.In this paper, we use the JED-SAD model to describe the evolution of theaccretion flow in the black hole transient MAXI J1820+070 during its hard andhard-intermediate states. Contrarily to the previous applications of thismodel, the Compton reflection component has been taken into account. We useeight broadband X-rays spectra, including NuSTAR, NICER and Swift data,providing a total spectral coverage of 0.8-190 keV. The data were directlyfitted with the JED-SAD model. Our results suggest that the optically thickdisk (i.e. the SAD) does not extend down to the ISCO in any of the consideredepochs. In particular, as the system evolves towards the hard/intermediatestate, we find that the inner radius decreases from $\sim$60 R$_{\rm G}$ in thefirst observation down to $\sim$30 R$_{\rm G}$ in the last one. This trend isaccompanied by an increase of the mass-accretion rate. In all hard-intermediatestate observations, two reflection components, characterized by differentvalues of ionization, are required to adequately explain the data. Thesecomponents likely originate from different regions of the SAD. We show that aflared outer disk could, in principle, explain the double reflection component.

Tracking the evolution of the accretion flow in MAXI J1820+070 during its hard state with the JED-SAD model