CCA Colloquium: P. Chris Fragile

Title: The Luminous, Hard State Can’t Be MAD

Abstract: I will present a straightforward argument for why the luminous, hard state of black hole X-ray binaries (BHXRBs) cannot always be associated with a magnetically arrested accretion disc (MAD). This is significant as MADs are often invoked to explain the hard state and are becoming the preferred model by many numericists. My argument relies on three core premises: (1) that the type-C quasi-periodic oscillation (QPO) is best explained by Lense–Thirring (LT) precession of a tilted, inner, hot flow; (2) that observed optical and infrared (IR) QPOs with the same or lower frequency as the type-C QPO suggest the jet, too, must precess in these systems; and (3) that numerical simulations of MADs show that their strong magnetic fields promote alignment of the disc with the black hole and, thereby, suppress LT precession. In my talk, I will present supporting evidence for all three premises. In the end, if we accept them all as true, then, at least whenever the optical and IR QPOs are observed alongside the type-C QPO, these systems cannot be in the MAD state. Extending the argument further, if the type-C QPO is always associated with LT precession, then it would rule out MADs anytime this timing feature is seen, which covers nearly all BHXRBs when they are in the luminous, hard and hard-intermediate states. At the end of my talk, I will discuss possible alternatives to my conclusions.

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