Nuclear de-excitation line spectrum of Cassiopeia A

TL;DR

This paper predicts nuclear de-excitation line fluxes from Cassiopeia A based on hadronic cosmic ray interactions, comparing the results with COMPTEL measurements to understand the origin of gamma-ray emissions.

Contribution

It provides the first detailed prediction of nuclear line spectra from Cassiopeia A assuming a hadronic origin, connecting cosmic ray spectra with gamma-ray observations.

Findings

Predicted nuclear line fluxes are near COMPTEL sensitivity levels.

Results support a hadronic origin for high-energy gamma rays in Cassiopeia A.

Predictions align with existing upper limits from observations.

Abstract

The supernova remnant Cassiopeia A is a prime candidate for accelerating cosmic ray protons and ions. Gamma rays have been observed at GeV and TeV energies, which indicates hadronic interactions, but they could also be caused by inverse-Compton scattering of low-energy photons by accelerated electrons. We seek to predict the flux of nuclear de-excitation lines from Cas A through lower-energy cosmic rays and to compare it with COMPTEL measurements. Assuming a hadronic origin of the high-energy emission, we extrapolate the cosmic ray spectrum down to energies of 10 MeV, taking into account an equilibrium power-law momentum spectrum with a constant slope. We then calculate the nuclear line spectrum of Cassiopeia A, considering the most prominent chemical elements in the MeV band and their abundances as determined by X-ray spectroscopy. We show that the predicted line spectrum is close to the level of the COMPTEL sensitivity and agrees with conservative upper limits.