Kim, Junhan, Marrone, Daniel P., Roy, Alan L., Wagner, Jan, Asada, Keiichi, Beaudoin, Christopher, Blanchard, Jay, Carlstrom, John E., Chen, Ming-Tang, Crawford, Thomas M., Crew, Geoffrey B., Doeleman, Sheperd S., Fish, Vincent L., Greer, Christopher H., Gurwell, Mark A., Henning, Jason W., Inoue, Makoto, Keisler, Ryan, Krichbaum, Thomas P., Lu, Ru-Sen, Muders, Dirk, Müller, Cornelia, Nguyen, Chi H., Ros, Eduardo, SooHoo, Jason et al. 2018. "The 1.4 mm Core of Centaurus A: First VLBI Results with the South Pole Telescope." The Astrophysical Journal 861:129. https://doi.org/10.3847/1538-4357/aac7c6
Centaurus A (Cen A) is a bright radio source associated with the nearby galaxy NGC 5128 where high-resolution radio observations can probe the jet at scales of less than a light day. The South Pole Telescope (SPT) and the Atacama Pathfinder Experiment performed a single-baseline very-long-baseline interferometry (VLBI) observation of Cen A in 2015 January as part of VLBI receiver deployment for the SPT. We measure the correlated flux density of Cen A at a wavelength of 1.4 mm on a ~7000 km (5 Glambda) baseline. Ascribing this correlated flux density to the core, and with the use of a contemporaneous short-baseline flux density from a Submillimeter Array observation, we infer a core brightness temperature of 1.4 × 1011 K. This is close to the equipartition brightness temperature, where the magnetic and relativistic particle energy densities are equal. Under the assumption of a circular Gaussian core component, we derive an upper limit to the core size varphi = 34.0 ± 1.8 muas, corresponding to 120 Schwarzschild radii for a black hole mass of 5.5 × 107 M &sun;.