We report the discovery of a strongly lensed arc system around a field elliptical galaxy in Hubble Space Telescope ( HST ) Advanced Camera for Surveys ( ACS ) images of a parallel field observed during NICMOS observations of the HST Ultra-Deep Field .
The ACS parallel data comprise deep imaging in the F435W , F606W , F775W , and F850LP bandpasses .
The main arc is at a radius of 1 \farcs 6 from the galaxy center and subtends about 120 ^ { \circ } .
Spectroscopic follow-up at Magellan Observatory yields a redshift z = 0.6174 for the lensing galaxy , and we photometrically estimate z _ { phot } = 2.4 \pm 0.3 for the arc .
We also identify a likely counter-arc at a radius of 0 \farcs 6 , which shows structure similar to that seen in the main arc .
We model this system and find a good fit to an elliptical isothermal potential of velocity dispersion \sigma \approx 300 km s ^ { -1 } , the value expected from the fundamental plane , and some external shear .
Several other galaxies in the field have colors similar to the lensing galaxy and likely make up a small group .