1.3 mm Wavelength VLBI of Sagittarius A*: Detection of Time-variable Emission on Event Horizon Scales

Citation:

Vincent L. Fish, Sheperd S. Doeleman, Christopher Beaudoin, Ray Blundell, David E. Bolin, Geoffrey C. Bower, Richard Chamberlin, Robert Freund, Per Friberg, Mark A. Gurwell, Mareki Honma, Makoto Inoue, Thomas P. Krichbaum, James Lamb, Daniel P. Marrone, James M. Moran, Tomoaki Oyama, Richard Plambeck, Rurik Primiani, Alan E. E. Rogers, Daniel L. Smythe, Jason SooHoo, Peter Strittmatter, Remo P. J. Tilanus, Michael Titus, Jonathan Weintroub, Melvyn Wright, David Woody, Ken H. Young, and Lucy M. Ziurys. 2011. “1.3 mm Wavelength VLBI of Sagittarius A*: Detection of Time-variable Emission on Event Horizon Scales.” The Astrophysical Journal Letters, 727.

Abstract:

Sagittarius A*, the ~4 × 106 M sun blackhole candidate at the Galactic center, can be studied on Schwarzschildradius scales with (sub)millimeter wavelength very long baselineinterferometry (VLBI). We report on 1.3 mm wavelength observations ofSgr A* using a VLBI array consisting of the JCMT on Mauna Kea, theArizona Radio Observatory's Submillimeter Telescope on Mt. Graham inArizona, and two telescopes of the CARMA array at Cedar Flat inCalifornia. Both Sgr A* and the quasar calibrator 1924-292 were observedover three consecutive nights, and both sources were clearly detected onall baselines. For the first time, we are able to extract 1.3 mm VLBIinterferometer phase information on Sgr A* through measurement ofclosure phase on the triangle of baselines. On the third night ofobserving, the correlated flux density of Sgr A* on all VLBI baselinesincreased relative to the first two nights, providing strong evidencefor time-variable change on scales of a few Schwarzschild radii. Theseresults suggest that future VLBI observations with greater sensitivityand additional baselines will play a valuable role in determining thestructure of emission near the event horizon of Sgr A*.