We present a \gamma -ray photon flux and spectral variability study of the flat-spectrum radio quasar 3C 273 over a rapid flaring activity period between September 2009 to April 2010 .
Five major flares are observed in the source during this period .
The most rapid flare observed in the source has a flux doubling time of 1.1 hr .
The rapid \gamma -ray flares allow us to constrain the location and size of the \gamma -ray emission region in the source .
The \gamma \gamma -opacity constrains the Doppler factor , \delta _ { \gamma } \geq 10 for the highest energy ( 15 GeV ) photon observed by the Fermi -Large Area Telescope ( LAT ) .
Causality arguments constrain the size of the emission region to 1.6 \times 10 ^ { 15 } cm .
The \gamma -ray spectra measured over this period show clear deviations from a simple power law with a break in 1-2 GeV energy range .
We discuss possible explanations for the origin of the \gamma -ray spectral breaks .
Our study suggests that the \gamma -ray emission region in 3C 273 is located within the broad line region ( < 1.6 pc ) .
The spectral behavior and temporal characteristics of the individual flares indicate the presence of multiple shock scenarios at the base of the jet .