On the Hadronic Origin of High Energy Emission of $\gamma$-ray Loud Narrow-Line Seyfert 1 PKS 1502+036

TL;DR

This paper investigates whether the high-energy emission of the gamma-ray loud NLS1 galaxy PKS 1502+036 is better explained by leptonic or hadronic processes, finding leptonic models more consistent with observations.

Contribution

The study compares leptonic and lepto-hadronic models for the SED of PKS 1502+036, concluding leptonic processes are favored for its high-energy emission.

Findings

Leptonic model reproduces the observed SED effectively.

Proton synchrotron can explain high-energy emission but requires extreme parameters.

pγ interactions and cascade processes cannot account for the SED.

Abstract

The radiation mechanism of Radio-Loud Narrow-Line Seyfert 1 (RL-NLS1) from X-ray to $\gamma$-ray bands remains an open question. While the leptonic model has been employed to explain the spectral energy distribution (SED), the hadronic process may potentially account for the high energy radiation of some $\gamma$-ray loud Narrow-Line Seyfert 1 (NLS1) as well. We study one of such RL-NLS1, PKS 1502+036, comparing the theoretical SEDs predicted by the leptonic model and the lepto-hadronic model to the observed one. For the hadronic processes, we take into account the proton synchrotron radiation and proton-photon interactions (including the Bethe-Heitler process and the photopion process) including the emission of pairs generated in the electromagnetic cascade initiated by these processes. Our results show that the leptonic model can reproduce the SED of this source, in which the X-ray to $\gamma$-ray radiation can be interpreted as the inverse Compton (IC) scattering. On the other hand, the proton synchrotron radiation can also explain the high energy component of SED although extreme parameters are needed. We also demonstrate that the $p\gamma$ interactions as well as the cascade process cannot explain SED. Our results imply that a leptonic origin is favored for the multi-wavelength emission of PKS 1502+036.