Looking to the future: using IR interferometry to study microquasars

Infrared interferometry is currently in a rapid development phase, with new instrumentation soon achieving milliarcsecond spatial resolutions for faint sources and astrometry on the order of 10 microarcseconds. For jet studies in particular, the next generation of instruments will bring us closer to the event horizon of supermassive black holes such as Sgr A*, and the region where jet launching must occur. But a new possibility to study microquasars in general and jet physics in particular may also arise, using techniques similar to those employed for finding faint exoplanets around stars. The compact, steady jets observed in the hard state of X-ray binaries display a flat/inverted spectrum from the lower radio wavelengths up through at least the far-IR band. Somewhere above this band, a turnover is predicted where the jets become optically thin, revealing a power-law spectrum. This break may have been observed directly in GX339-4, but in most sources such a feature is likely hidden under bright emission from the stellar companion or accretion disk components. Detecting the exact location of this break would provide a new constraint on our models of jet physics, since the break frequency is dependent on the total power, as well as internal density and magnetic field. Furthermore, knowing the break location combined with the spectral index of the power-law would help constrain the amount of synchrotron emission contributed by the jets to the X-ray bands. Along with a summary of some potential observations requiring less optimal instrumental specifications, I will discuss a technique which may enable us to discern the jet break, and the chances of success based on theoretical models applied to some potential target sources.