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The flat spectrum radio quasar CTA 102 entered an extended period of activityfrom 2016 to 2017 during which several strong $\gamma$-ray flares wereobserved. Using Fermi large area telescope data a detailed investigation of\gray spectra of CTA 102 during the flaring period is performed. In severalperiods the \gray spectrum is not consistent with a simple power-law, having ahard photon index with an index of $\sim(1.8-2.0)$ that shows a spectral cutoffaround an observed photon energy of $\sim(9-16)$ GeV. The internal $\gamma$-rayabsorption via photon-photon pair production on the broad-line-region-reflectedphotons cannot account for the observed cut-off/break even if the emittingregion is very close to the central source. This cut-off/break is likely due toa similar intrinsic break in the energy distribution of emitting particles. Theorigin of the spectral break is investigated through the multiwavelengthmodeling of the spectral energy distribution, considering a different locationfor the emitting region. The observed X-ray and $\gamma$-ray data is modeled asinverse Compton scattering of synchrotron and/or external photons on theelectron population that produce the radio-to-optical emission which allowed toconstrain the power-law index and cut-off energy in the electron energydistribution. The obtained results are discussed in the context of a diffusiveacceleration of electrons in the CTA 102 jet.

Investigation of the Gamma-ray Spectrum of CTA 102 During the Exceptional Flaring State in 2016-2017