Role of magnetically dominated disc-outflow symbiosis on bright hard-state black hole sources: ultra-luminous X-ray sources to quasars

Abstract

ABSTRACTWe present optically thin solutions for magnetized, advective disc-outflow symbiosis around black holes (BHs). The main objective is to explain the bright, hard-state observations of accreting systems with stellar mass-to-supermassive BHs. We include the effects of magnetic fields and radiation counterpart in entropy gradient based on the first law of thermodynamics to represent energy advection. The cooling process includes bremsstrahlung, synchrotron radiation, and inverse Comptonization process. One of our main ventures is to explain some long-standing issues of ultra-luminous X-ray sources (ULXs). The existing physical scenarios to explain their unusual high luminosity are either the existence of the missing class of intermediate-mass BH (IMBH) or super-Eddington accretion around a stellar-mass BH. However, most ULXs with steep power-law spectrum can be well explained through super-Eddington accretion, while the existence of IMBH is indeed disputed extensively. Nevertheless, the interpretation of ULXs with a hard power-law-dominated state remains mysterious. Here we show that our magnetically dominated disc-outflow symbiosis around rapidly spinning stellar-mass BHs can achieve such large luminosity even for sub-Eddington accretion rate. The magnetic field at the outer zone of the advective flow is more than the corresponding Eddington limit. Such a field becomes dynamically dominant near the BH through continuous accretion process due to flux freezing, but maintaining its Eddington limit. This unique field configuration enhances the synchrotron and synchrotron self-Comptonization process to achieve very large luminosity. Through the same mechanism, our solutions for supermassive BHs can explain the unusual large luminosity of ultra-luminous quasars.