We present new z \sim 8 galaxy candidates from a search over \sim 95 arcmin ^ { 2 } of WFC3/IR data , tripling the previous search area for bright z \sim 8 galaxies .
Our analysis uses newly acquired WFC3/IR imaging data from the CANDELS Multi-Cycle Treasury program over the GOODS South field .
These new data are combined with existing deep optical ACS imaging to search for relatively bright ( M _ { UV } < -19.5 mag ) z \sim 8 galaxy candidates using the Lyman Break technique .
These new candidates are used to determine the bright end of the UV luminosity function ( LF ) of star-forming galaxies at z \sim 7.2 - 8.7 , i.e .
a cosmic age of 600 \pm 80 Myr .
To minimize contamination from lower redshift galaxies , we make full use of all optical ACS data and impose strict non-detection criteria based on an optical \chi ^ { 2 } _ { opt } flux measurement .
In the whole search area we identify 16 candidate z \sim 8 galaxies , spanning a magnitude range H _ { 160 ,AB } = 25.7 - 27.9 mag .
The new data show that the UV LF is a factor \sim 1.7 lower at M _ { UV } < -19.5 mag than determined from the HUDF09 and ERS data alone .
Combining this new sample with the previous candidates from the HUDF09 and ERS data allows us to perform the most accurate measurement of the z \sim 8 UV LF yet .
Schechter function fits to the combined data result in a best-fit characteristic magnitude of M _ { * } ( z = 8 ) = -20.04 \pm 0.46 mag .
The faint-end slope is very steep , though quite uncertain , with \alpha = -2.06 \pm 0.32 .
A combination of wide area data with additional ultra-deep imaging will be required to significantly reduce the uncertainties on these parameters in the future .