Spectral Mapping of Black Hole Accretion Disks at Critical, Fast Timescales
Abstract
Galactic X-ray binaries are the brightest available laboratories for studying strong gravity. Crucially, X-ray binaries are also dynamic systems, with a typical transient binary exhibiting months-long outbursts interspersed with decades of quiescence. During outburst, a typical X-ray binary evolves through a range of accretion states and luminosities, reaching its Eddington limit. The importance of monitoring these brightest systems has been most readily demonstrated through the paradigmatic advancments achieved with spectral-timing breakthrough mission RXTE, which now set the foundation by which X-ray binary systems are understood. This spectral-timing legacy is being advanced through the ongoing NICER and ASTROSAT missions. As two prominent and salient examples of the scientific gains associated with advancements in spectral-timing capabilities, continuum spectral models of the brightest X-ray binary systems have been used to produce constraints on neutron-star equation of state and measurements of black hole spin. A generational successor spectral-timing instrument such as STROBE-X, will revolutionize our understanding of the accretion process as dramatically as did RXTE. Through its large collecting area and high time resolution, our ability to fully mine the wealth of information carried by our Galactic sources by reaching the last remaining critical timescales, can be achieved. At the limits of current capabilities, we are now able to spectrally probe the viscous timescale at the innermost edge of the accretion disk; a generational advance will reach thermal and dynamical timescales! Reachign these high count rates will enable direct spectral study of the structural changes which occur over cycles of quasi-periodic oscillations (QPOs), for even the fastest QPOs. This is essential in order to reveal the physical driving mechanisms of these oscillations, and of particular importance given the widely-held expectation that high-frequency QPOs in stellar-mass black holes (at hundreds of Hz) should be the highest precision markers of black-hole spin.
- Publication:
-
AAS/High Energy Astrophysics Division
- Pub Date:
- March 2019
- Bibcode:
- 2019HEAD...1720503S