Constraints on the minimum electron lorentz factor and matter content of jets for a sample of bright fermi blazars

Abstract

We fit (quasi-)simultaneous multi-waveband spectral energy distributions for a sample of low-synchrotron-peaked (LSP) blazars with a one-zone leptonic model. The seed photons that predominantly come from the broad line region (BLR) and infrared (IR) molecular torus are considered in the context of an external Compton process. We find that modeling with IR seed photons is systematically better than that with BLR photons based on a χ2 test, which suggests that γ-ray-emitting regions are most likely found outside the BLR. The minimum electron Lorentz factor, γ min, is constrained from the modeling of these LSP blazars with good soft X-ray data (ranging from 5 to 160 with a median value of 55), which plays a key role in jet power estimation. Assuming a one-to-one ratio of protons to electrons, we find that the jet power for LSP blazars is systematically higher than that of FR II radio galaxies at a 151 MHz radio luminosity, L 151 MHz even though FR IIs are regarded as the same as LSP blazars in a unification scheme except at the jet viewing angle. A possible reason for this is that there are some e ± pairs in the jets of these blazars. If this is the case, we find that the number density of e ± pairs should be several times higher than that of e --p pairs by assuming the jet power is the same for LSP blazars and FR IIs at the given L 151 MHz.