I present a study of the high-energy \gamma -ray properties of the flat spectrum radio quasar , PKS 1510-089 , based on 3.75 years of observations with the Large Area Telescope ( LAT ) detector on-board the Fermi \gamma -ray Space Telescope .
Throughout the observing period , the 0.1 GeV < E _ { \gamma } < 300 GeV \gamma -ray flux was highly variable , undergoing several flaring events where the daily flux exceeded 10 ^ { -5 } photons cm ^ { -2 } s ^ { -1 } on 3 separate occasions .
The increased photon statistics of these large flares allowed the observations to be re-analysed in 6 and 3 hour intervals , revealing flux doubling timescales as small as 1.3 \pm 0.12 hours during the flare rise time , and flux halving timescales of 1.21 \pm 0.15 hours during the flare decay .
These are the smallest variability timescales measured to date at MeV - GeV energies for the Flat Spectrum Quasar class of Active Galactic Nuclei .

The > 10 ^ { -5 } photons cm ^ { -2 } s ^ { -1 } flare events were also studied in more detail in an attempt to uncover evidence for the location of PKS 1510-089 ’ s \gamma -ray emission region .
In particular , two approaches were used : ( i ) searching for an energy dependence to the cooling timescales , and ( ii ) searching for evidence of a spectral cut-off .
The combined results of these two approaches , along with the confirmation of \geq 20 GeV photon flux from PKS 1510-089 , suggest the presence of multiple \gamma -ray emission regions being located in both the broad line region and molecular torus region of PKS 1510-089 .

An analysis of the highest photon events within the 3.75 year data set finds PKS 1510-089 to be a source of \geq 20 GeV \gamma -rays at the 13.5 \sigma confidence level ; a observational property which is difficult to explain in the traditional view that \gamma -ray emission from Active Galactic Nuclei originates from the base of the relativistic jet .
This gives further weight to the argument that there are multiple , simultaneously active \gamma -ray emission regions located along the relativistic jet of Active Galactic Nuclei .