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We present preliminary results of our analysis of the {\it Fermi}-LAT datafrom the direction of NGC 4151. We find a new gamma-ray source with astatistical significance sigma > 5, shifted by 0.5degr from the position of NGC4151. Apparently, the source was bright only during a 1.5-year period betweenDecember 2011 and June 2013 and it strongly contaminated the signal from NGC4151. Therefore, we neglect this period in our analysis. We find twoadditional, persistent gamma-ray sources with high sigma, shifted from NGC 4151by ~1.5degr and 5degr, whose presence has been recently confirmed in the ThirdFermi Catalog. After subtracting the above sources, we still see a weakresidual, with sigma ~< 3, at the position of NGC 4151. We derive an upperlimit (UL) for the gamma-ray flux from NGC 4151 and we compare it withpredictions of the ADAF model which can explain the X-ray observations of thisobject. We find that the Fermi UL strongly constrains non-thermal accelerationprocesses in hot flows as well as the values of some crucial parameters. Herewe present the comparison with the hot flow models in which heating ofelectrons is dominated by Coulomb interactions with hot protons. In such aversion of the model, the gamma-ray UL, combined with the X-ray data,constrains the energy content in the non-thermal component of protondistribution to at most a few per cent, rules out a weak (sub-equipartition)magnetic field and favors a rapid rotation of the supermassive black hole.

Fermi-LAT Upper Limit for NGC 4151 and its Implications for Physics of Hot Accretion Flow