We report on our study of the high-energy \gamma - ray emission from the FR I radio galaxy NGC 1275 , based on two years of observations with the Fermi -LAT detector .
Previous Fermi studies of NGC 1275 had found evidence for spectral and flux variability on monthly timescales during the first year of Fermi -LAT observations .
This variability is also seen in the larger two year data set , during which we observe a large \gamma - ray flare ( June-August 2010 ) .
The increased photon statistics from this large flare have allowed the discovery of flux variability from NGC 1275 on the timescales of days .
The largest flux variation observed during this flare being a factor of \sim 3 from one day to the next and a resultant e -folding risetime of 1.51 \pm 0.2 days .
The two year averaged E > 100 MeV \gamma - ray spectrum is adequately described by a power-law spectrum , with a photon index , \Gamma , of 2.09 \pm 0.02 , and a resultant integrated flux of F _ { \gamma } = ( 2.2 \pm 0.1 ) \times 10 ^ { -7 } ph cm ^ { -2 } s ^ { -1 } .
While no hysteresis was observed in the photon index - flux ( \Gamma _ { \gamma } vs F _ { \gamma } ) parameter space , there was obvious ‘ harder-when-brighter ’ behaviour observed during the large \gamma - ray flare .
Furthermore , during this large flare , NGC 1275 appeared to migrate from the FR I radio galaxy to the BL Lac object region of the photon index - luminosity ( \Gamma _ { \gamma } vs L _ { \gamma } ) paramater space .
In this paper we present details of our Fermi -LAT analysis of NGC 1275 , including a brief discussion on its implications for \gamma - ray blazar sources .