SIMBAD references

The broad-band spectral energy distributions (SEDs) of blazars exhibit two broad spectral components which in leptonic emission models are attributed to synchrotron radiation and synchrotron self-Compton (SSC) radiation of relativistic electrons. During high-state phases, the high-frequency SSC component dominates over the low-frequency synchrotron component implying that the inverse Compton SSC losses of electrons are at least equal or greater than the synchrotron losses of electrons. The linear synchrotron cooling, included routinely in radiation models of blazars, then has to be replaced by the SSC cooling. It is shown that the SSC energy-loss rate of electrons calculated in the Thomson limit (SST cooling) depends on an energy integral of the actual electron spectrum, reflecting the dependence of the energy density of the target synchrotron photons on the differential electron energy spectrum. The dependence of the SST loss rate on the initial kinetic energy of injected electrons is a collective effect completely different from the linear synchrotron cooling case. For the illustrative case of instantaneous injection of monoenergetic particles, we solve the non-linear kinetic equation for the intrinsic temporal evolution of the relativistic particles under SST cooling and compare the solution with the standard linear synchrotron cooling solution. For standard blazar emission region parameters, we find that under SST cooling electrons cool much more rapidly than in linear synchrotron cooling. The different cooling behaviour of electrons implies differences for the optically thin synchrotron and SSC radiation intensity and fluence energy spectra. The first difference concerns the duration of the SSC flare at different scattered photon energies. At large SSC photon energies, the SST cooled duration time is much smaller than the synchrotron cooled duration time, whereas at small SSC photon energies the SST cooled flare lasts much longer than the synchrotron cooled flare. Secondly, strong differences in the spectral behaviour of the total SSC fluence occur. At low scattered photon energies, the synchrotron cooled total SSC fluence exhibits a flatter (∝ k^–1/4_s) power-law behaviour than the SST cooled total SSC fluence (∝ k^–3/4_s). Thirdly, the SST cooled total synchrotron fluence exhibits a steeper (by Δα = 1) power-law behaviour [F_T(ε) ∝ ε^–3/2] than the synchrotron cooled total synchrotron fluence [F_S(ε) ∝ ε^–1/2] below the same exponential cut-off energy. These predictions of spectral behaviour with time and frequency provide conclusive tests for the presence or absence of linear synchrotron cooling or non-linear SST cooling in flaring non-thermal sources.