High Energy Gamma Rays from Protons Hitting Compact Objects

TL;DR

This paper models gamma ray production from protons hitting compact objects, predicting a characteristic spectral dip below 70 MeV and explaining observed galactic center gamma rays.

Contribution

It generalizes previous positron spectrum calculations to include gamma rays from pi0 decay, linking gamma spectra to high-energy proton spectra for various compact objects.

Findings

Gamma ray spectrum shows a dip below 70 MeV.

Spectrum largely independent of the compact object’s mass.

Model explains gamma rays observed at the galactic center.

Abstract

In a previous paper the spectrum of positrons produced by matter initially at rest falling onto a massive compact object was calculated. In this paper this calculation is generalized to obtain both the spectrum of in-flight positron annihilation and pi0 decay gamma rays produced when protons with a cosmic ray-like spectrum hit the surface. The resulting pi0 decay gamma ray spectrum reflects the high energy proton energy spectrum, and is largely independent of the mass of the compact object. One notable prediction for all compact objects is a dip in the spectrum below 70 MeV. As applied to the 10^6 solar mass massive compact object near to the center of our galaxy, our theory shows promise for explaining the gamma rays coming from the galactic center as observed by both the Compton satellite and HESS ground based array.