Gamma Rays from the Tycho Supernova Remnant: Leptonic or Hadronic?

TL;DR

This paper investigates whether gamma-ray emissions from the Tycho supernova remnant are caused by leptonic processes involving electrons or hadronic processes involving protons, using spectral data and modeling.

Contribution

It demonstrates that a two-zone leptonic model can explain Tycho's gamma-ray spectrum and suggests how to confirm hadronic origins through future spectral measurements.

Findings

Leptonic model explains Tycho's gamma-ray spectrum.

Hadronic model also fits the data.

Future observations can distinguish the origin.

Abstract

Recent Fermi and VERITAS observations of the prototypical Type Ia supernova remnant (SNR) Tycho have discovered gamma-rays with energies E in the range from ~0.4 GeV to 10 TeV. Crucial for the theory of Galactic cosmic-ray origin is whether the gamma-rays from SNRs are produced by accelerated hadrons (protons and ions), or by relativistic electrons. Here we show that the broadband radiation spectrum of Tycho can be explained within the framework of a two-zone leptonic model, which is likely to apply to every SNR. A model with hadrons can also fit the radiation spectrum. The hadronic origin of gamma-rays can be confirmed by Fermi spectral measurements of Tycho and other SNRs at energies below ~300 MeV.