X-ray Spectra From Weakly Magnetized Accretion Flows

In this paper, we expand upon previous work that argued for the possibility of a sub-equipartition magnetic field in the accretion flow of a black hole binary system. Using X-ray observations of the three well-known sources A0620-00, XTE J1118+480 and V404 Cyg during the quiescent state, we compare the theoretically expected spectral shape with the observed data in order to verify that the parameters of the sub-equipartition model are plausible. In all three cases, we find that it is possible to reproduce the spectral shape of the X-ray observations with a sub-equipartition flow. These findings support the idea that the quiescent state spectrum of X-ray binary systems is produced by a weakly-magnetized accretion flow. A sub-equipartition flow would pose a significant challenge to our current understanding of jet-launching, which relies on the presence of a strong magnetic field to power the jet.