Disc winds and jets are ubiquitous among accreting systems on all scales, from active galactic nuclei (AGN) down to young stellar objects. They represent a key mechanism through which these systems interact with their environment (“feedback") and may be responsible for triggering the mysterious state changes observed in X-ray binary stars (XRBs).
Transient low-mass X-ray binaries (LMXBs), harbouring a black hole or a neutron star, provide us with a natural laboratory for studying the connection(s) between accretion discs, jets and winds. These systems undergo outbursts, during which they brighten dramatically across the whole electromagnetic spectrum. The outbursts typically last hundreds of days, recur on timescales of decades, and reflect a sudden increase in the accretion rate onto the compact object. Over the course of an outburst, LMXBs exhibit two distinct spectral states. These spectral states are thought to be a consequence of different accretion geometries close to the central object.
Remarkably, the two distinct accretion states also appear to produce two distinct types of outflows. Steady compact radio jets are only seen in the hard state, whereas evidence of disc winds originally came in the form of blue-shifted X-ray absorption lines associated with Fe ions detected only during the soft state. However, recent observations of disc winds in the far-UV, optical and NIR lines reveal a multiphase nature of these outflows that may be present across the entire outburst.
I will discuss the current status of disc winds in LMXBs with special emphasis in the latest results from far-UV spectroscopy obtained with the Hubble Space Telescope.