The nature of gamma-ray emission of Tycho's supernova remnant

TL;DR

This paper models the gamma-ray emission of Tycho's supernova remnant using nonlinear cosmic ray acceleration theory, explaining the observed spectrum as a superposition from different interstellar medium phases, and confirms efficient cosmic ray production.

Contribution

It introduces a model accounting for clumpy interstellar medium effects on gamma-ray emission, providing a comprehensive explanation for Tycho's SNR observations and cosmic ray acceleration efficiency.

Findings

Gamma-ray spectrum explained by two ISM phases

Efficient cosmic ray production confirmed in Tycho's SNR

Excess GeV emission due to cloud contribution

Abstract

The nature of the recently detected HE and VHE gamma-ray emission of Tycho's supernova remnant (SNR) is studied. A nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) is employed to investigate the properties of Tycho's SNR and their correspondence to the existing experimental data, taking into account that the ambient interstellar medium (ISM) is expected to be clumpy. It is demonstrated that the overall steep gamma-ray spectrum observed can be interpreted as the superposition of two spectra produced by the CR proton component in two different ISM phases: The first gamma-ray component, extending up to about $10^{14}$ eV, originates in the diluted warm ISM, whereas the second component, extending up to 100 GeV, comes from numerous dense, small-scale clouds embedded in this warm ISM. Given the consistency between acceleration theory and the observed properties of the nonthermal emission of Tycho's SNR, a very efficient production of nuclear CRs in Tycho's SNR is established. The excess of the GeV gamma-ray emission due to the clouds' contribution above the level expected in the case of a purely homogeneous ISM, is inevitably expected in the case of type Ia SNe.