Effects of non-continuous inverse Compton cooling in blazars

Abstract

Flaring states of blazars are ideally suited to study the extreme physics of relativistic outflows. A thorough understanding of particle acceleration and cooling mechanisms operating in blazar jets can be achieved via physical modeling of varying multi-band flaring emission from the radio up to the gamma-ray range. The majority of the numerical codes developed for this task use a simplified continuous-loss description for the inverse Compton particle cooling. Such an approximation is however no longer valid in the Klein-Nishina (KN) regime, as particles suffer large relative jumps in energy. In our study, we explore the importance of non-continuous (discrete) Compton cooling losses and their effect on the blazar electron spectrum and broad-band spectral energy distribution (SED) for typical physical conditions during blazar gamma-ray flares. We solve numerically the full transport equation that takes into account large relative jumps in energy, and simulate the time-dependent electron spectrum and SED for the conditions of extreme flares of the Flat Spectrum Radio Quasar (FSRQ) 3C 279. We find that non-continuous cooling can significantly modify the shape of the electron spectrum, resulting in notable differences up to ~35 - 40% in the corresponding SED during extreme flaring states.