Leptonic and Hadronic Modeling of Fermi-LAT Hard Spectrum Quasars and Predictions for High-Energy Polarization

Understand

We present the results of a study of the time-averaged spectral energy distributions (SEDs) of eight flat spectrum radio quasars (FSRQs) present in the second catalog of high energy sources detected beyond 50 GeV by the {\it Fermi}-Large Area Telescope (2FHL).

• Both leptonic and hadronic scenarios are adopted to explain the multi-wavelength SEDs and we find them to be marginally consistent with the 2FHL spectra above 50 GeV.
• We derive the expected degree of X-ray and $\gamma$-ray polarizations both for the average and elevated activity states and note that: (i) a hadronic radiative model consistently predicts a higher degree of high energy polarization compared to leptonic ones, and (ii) the X-ray polarization degree is higher than the $\gamma$-ray polarization in the leptonic scenario, but similar to the $\gamma$-ray polarization if the observed radiation is powered by hadronic processes.
• From the leptonic modeling, the location of the $\gamma$-ray emitting region is found to be at the outer edge of the broad line region (BLR) and is consistent with the $\gamma\gamma$ opacity estimates for the $\gamma$-ray absorption by the BLR.