Compton-induced HE -- VHE $γ$-rays from pair cascade emissions in the SEDs of radio galaxies: NGC 1275

Abstract: In the scheme of active galactic nuclei (AGNi), the blazar subclass is particularly bright in $γ$-rays. This is because of their emissions being beamed into our line of sight, as opposed to their misaligned parent population, radio galaxies. This work presents results of a Monte-Carlo code that propagates jet-collimated $γ$-rays through the magnetized AGN environment, leading to secondary cascade emissions from relativistic electron-positron pairs. The resulting multi-wavelength emissions are used to fit the broadband spectral energy distribution (SED) of the radio galaxy NGC 1275. Using known physical parameters of NGC 1275 from the literature, we find that cascade emissions from stochastic processes have the potential to reproduce the broadband SEDs of radio galaxies. We also find that the interplay between accretion disk and broad-line region (BLR) photons may provide insights into the production region(s) of $γ$-rays in AGNi. While dense accretion disk and BLR radiation fields are vital to the development of cascades, excessive densities lead to the suppression of cascade synchrotron emission and attenuation of \,TeV $γ$-rays. Furthermore, the magnetic field is important in shaping the cascade $γ$-ray spectrum.