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We present results of spectrometric studies based on the observations of very strong 3C 279 flares in high and very-high-energy bands and discuss their implications regarding the origin of radiation mechanisms. The FSRQ 3C 279 (z=0.536) is one of the most luminous gamma-ray emitting AGN. It shows variability on time scales down to minutes during strong flares detected by the Fermi-LAT. We have analyzed LAT and Swift-XRT data for the flaring periods in June 2015 and January 2018, when the flux above 100 MeV during hourly time intervals could exceed $3 \times 10^{-5}$ ph cm$^{-2}$ s$^{-1}$. The X-ray flux derived from Swift X-ray observations described by a very hard spectrum with photon index ~1.5 is typically explained by Inverse Compton scattering of low energy electrons and protons. Here we consider an alternative interpretation which describes the entire band from X-ray to very high energy as a results of synchrotron emission by ultra relativistic electrons or protons.

Gamma-ray spectrometry in the cutoff region as a key for the understanding of radiation processes in 3C 279