Jet-dominated quiescent state in black hole X-ray binaries: the cases of A0620--00 and XTE J1118+480

TL;DR

This study shows that in the quiescent state of black hole X-ray binaries, most emission is jet-dominated, with hot accretion flows and outer cold discs contributing minimally, based on spectral analysis of two sources.

Contribution

It demonstrates that the quiescent state in these systems is primarily jet-dominated, supported by spectral modeling of two specific black hole X-ray binaries.

Findings

Most emission from radio to X-ray comes from the jet.

Hot accretion flow emission is negligible except in mid-infrared.

Outer cold disc emission is only visible in UV.

Abstract

The radiative mechanism of the black hole X-ray transients (BHXTs) in their quiescent states (defined as the 2-10 keV X-ray luminosity $\le 10^{34}{\rm \,erg\,s^{-1}}$) remains unclear. In this work, we investigate the quasi-simultaneous quiescent state spectrum (including radio, infrared, optical, ultraviolet and X-ray) of two BHXTs, A0620--00 and XTE J1118+480. We find that, these two sources can be well described by a coupled accretion -- jet model. More specifically, most of the emission (radio up-to infrared, and the X-ray waveband) comes from the collimated relativistic jet. Emission from hot accretion flow is totally insignificant, and it can only be observed in mid-infrared (the synchrotron peak). Emission from the outer cold disc is only evident in UV band. These results are consistent with our previous investigation on the quiescent state of V404 Cyg, and confirm that the quiescent state is jet-dominated.