Accretion disc–jet couplings in X-ray binaries

Abstract

When the matter from a companion star is accreted towards the central compact accretor, i.e. a black hole (BH) or a neutron star (NS), an accretion disc and a jet outflow will form, providing bight X-ray and radio emission, which is known as X-ray binaries (XRBs). In the low/hard state, there exist disc–jet couplings in XRBs, but it remains uncertain whether the jet power comes from the disc or the central accretor. Moreover, black hole X-ray binaries (BHXRBs) have different properties compared with neutron star X-ray binaries (NSXRBs): quiescent BHXRBs are typically two to three orders of magnitude less luminous than NSXRBs in X-ray, whereas BHXRBs are more radio loud than NSXRBs. In observations, an empirical correlation has been established between radio and X-ray luminosity, $L_{\rm R} \propto L_{\rm X}^b$, where b ∼ 0.7 for BHXRBs and b ∼ 1.4 for non-pulsating NSXRBs. However, there are some outliers of BHXRBs showing unusually steep correlation as NSXRBs at higher luminosities. In this work, under the assumption that the origin of jet power is related to the internal energy of the inner disc, we apply our magnetized, radiatively efficient thin disc model and the well-known radiatively inefficient accretion flow model to NSXRBs and BHXRBs. We find that the observed radio/X-ray correlations in XRBs can be well understood by the disc–jet couplings.

Explaining the ‘Outliers’ Track in Black Hole X-ray Binaries with a BZ-Jet and Inner-Disk Coupling

“…It is generally believed that the standard track in BHXBs is caused by the hot accretion flow (e.g., [10,12,60]). As shown in Section 3, the typical 'outliers' track is possibly caused by the BZ-jet at approximately the MAD state.…”

Black Hole Accretion with Saturated Magnetic Pressure and Disk Wind

“…In order to account for outflows in the analytical model, Blandford & Begelman (1999) assumed that the accretion rate has a power-law dependence on radius. Based on this assumption, many works have been carried out to study the structure and cooling mechanisms of the accretion disk with outflows (e.g., Gu 2015;Ghoreyshi & Shadmehri 2020;Shen & Gu 2020;Wu et al 2022). Recently, 2D analytical models revealed that the mass accretion rate indeed follows a power-law form (Xie & Yuan 2008;Dotan & Shaviv 2011;Gu 2012;Cao & Gu 2015;Kumar & Gu 2018;Feng et al 2019;Mosallanezhad et al 2021;Zeraatgari et al 2021).…”