  We report the discovery using Hubble Space Telescope imaging and Keck
spectroscopy of a very bright, highly magnified (~30*) Lyman Break Galaxy (LBG)
at z=3.07 in the field of the massive z=0.33 cluster MACSJ2135.2-0102. The
system comprises two high-surface brightness arcs with a maximum extent of 3",
bracketing a central object which we identify as a massive early-type galaxy at
z=0.73. We construct a lens model which reproduces the main features of the
system using a combination of a galaxy-scale lens and the foreground cluster.
We show that the morphological, spectral and photometric properties of the arcs
are consistent with them arising from the lensing of a single ~L* LBG. The most
important feature of this system is that the lensing magnification results in
an apparent magnitude of r=20.3, making this one of the brightest LBGs known.
Such a high magnification provides the opportunity of obtaining very high
signal to noise (and potentially spatially resolved) spectroscopy of a high
redshift galaxy to study its physical properties. We present initial imaging
and spectroscopy demonstrating the basic properties of the system and discuss
the opportunities for future observations.
