We present the discovery of an extremely bright and extended lensed source from the second Red Sequence Cluster Survey ( RCS2 ) .
RCSGA 032727-132609 is spectroscopically confirmed as a giant arc and counter-image of a background galaxy at z = 1.701 , strongly-lensed by the foreground galaxy cluster RCS2 032727-132623 at z = 0.564 .
The giant arc extends over \sim 38 ″and has an integrated r -band magnitude of 19.1 , making it \sim 20 times larger and \sim 3.5 times brighter than the prototypical lensed galaxy MS1512-cB58 .
This is the brightest distant lensed galaxy in the Universe known to date .
We have collected photometry in 9 bands , ranging from u to K _ { s } , which densely sample the rest-frame UV and optical light , including the age-sensitive 4000Å break .
A lens model is constructed for the system and results in a robust total magnification of 2.04 \pm 0.16 for the counter-image ; we estimate an average magnification of 17.2 \pm 1.4 for the giant arc based on the relative physical scales of the arc and counter-image on the sky .
Fits of single-component spectral energy distribution ( SED ) models to the photometry result in a moderately young age , t = 80 \pm 40 Myr , small amounts of dust , E ( B - V ) \leq 0.11 , and an exponentially declining star formation history with e -folding time \tau = 10 - 50 Myr .
After correcting for the lensing magnification , we find a stellar mass of M _ { * } \sim 10 ^ { 10 } M _ { \odot } and a current star formation rate SFR \leq 77 M _ { \odot } yr ^ { -1 } .
Allowing for episodic star formation , an underlying old burst could contain up to twice the mass inferred from single-component modeling .
RCSGA 032727-132609 is typical of the known population of star-forming galaxies near this redshift in terms of its age and stellar mass .
Its large magnification and spatial extent provide a unique opportunity to study the physical properties of an individual high-redshift star-forming galaxy in great detail , opening up a new window to the process of galaxy evolution between z = 1.7 and our local Universe .