Speaker
Description
We present an analysis of 8 years of Fermi-LAT γ-ray data obtained for NGC 1275. By examining the changes in its flux and spectral shape over the entire dataset, we found that its spectral behavior changed around 2011 February. The γ-ray spectra at the early times evolves largely at high energies, while the photon indices were unchanged in the latter despite rather large flux variations. To explain these observations, we suggest the flux changes in the early times were caused by injection of high-energy electrons into the jet, while later, the γ-ray flares were caused by a changing Doppler factor. To demonstrate the viability of these scenarios, we fit the broad-band spectral energy distribution data with a one-zone synchrotron self-Compton (SSC) model for flaring and quiescent intervals before and after 2011 February. To explain the γ-ray spectral behavior, the maximum electron Lorentz factor would have changed from γmax = 2.5 × 10^5 (quiescence) to γmax = 3.5 × 10^5 (flare) in the early times, while a modest change in the Doppler factor from δ = 2.7 to δ = 3.6 adequately fits the quiescent and flaring state γ-ray spectra in the later times.
