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“Radio Observations of Quiescent Black Hole X-Ray Binary Systems” Dr. James Miller-Jones NRAO |
| Black hole X-ray binary systems spend most of their time in a low-luminosity (L_x < 10^33.5 erg/s) `quiescent' state. In this state, and in the `hard' X-ray state seen at slightly higher luminosities, the radio and X-ray emission are seen to be well correlated, making such quiescent systems persistent, albeit faint, radio sources. The dynamics of the accretion flow at low mass accretion rates, and the importance of jets in carrying away the liberated accretion energy in such low-luminosity systems, are not yet well understood. Collimated, partially self-absorbed outflows are inferred to exist at higher mass accretion rates in the `hard' X-ray state, and have been directly imaged in two sources, GRS 1915+105 and Cygnus X-1. By studying the radio emission from quiescent systems, we can probe whether these jets persist and remain well-collimated at lower luminosities. Furthermore, since any such jets are weak, quiescent black hole X-ray binaries are persistent, core-dominated radio-emitting systems, which are good candidates for astrometric observations to measure their parallaxes and proper motions. In this talk, I will first give an overview of previous radio observations of quiescent black hole systems and what we have learned from them. I will then go on to present recent High Sensitivity Array (HSA) observations of the brightest quiescent black hole X-ray binary, V404 Cyg, which constrain the size and nature of the outflow in this system, with implications for the nature of the quiescent state. Using the HSA astrometric position, together with archival data, we were able to measure the proper motion of V404 Cyg. Taken together with the known position, radial velocity, and distance of the source, this can be used to infer its full three-dimensional space velocity, and its peculiar velocity with respect to its local standard of rest, allowing us to probe the formation mechanism of the black hole in this system. |