Program: GS-2019B-Q-233

From newborn stars and planets to supermassive black holes at the center of Galaxies, many astrophysical objects grow and evolve by accumulating mass through a disc. For these objects to grow, matter must lose angular momentum to flow inward, and avoid being removed from the system via outflows. However, our current understanding of the detailed physics governing angular momentum and mass transport in, and outflowing matter from, such discs is fragmented due to the limits of theoretical work and missing observational constraints. The recurring transient outbursts associated with matter flowing onto stellar-mass black holes in low-mass X-ray binaries (BH-LMXBs) provide us with strong test beds for constraining this poorly understood process of accretion. While these binary systems are far too small to be imaged directly, phase-resolved spectroscopy can provide a powerful diagnostic to study their highly complex, time-dependent accretion discs. Emission line profiles from these discs, observed in the optical and near-infrared (NIR) bands, encode within them a projection of the gas in the disc itself along the line of sight. Much like a CAT-scan uses X-ray images, taken at different angles, to reproduce a picture of complex structures inside the human body, through Doppler tomography, a 2- dimensional spectral data set can be used to draw a velocity-resolved ``blueprint'' of the line emission over an entire accretion disc, effectively creating an ``image'' of the disc on micro-arcsecond scales. The goal of this proposal is to combine (i) 17 hrs of phase-resolved spectroscopy of an outbursting BH-LMXB from Gemini/GMOS with (ii) modern Doppler tomography techniques, to understand the geometry and structure of the gas making up an outbursting BH-LMXB accretion disc.