Nuclear de-excitation line spectrum of Cassiopeia A

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.

4 pages, 1 figure, accepted for publication by A&A

References in corpus (4)

• The Cassiopeia A Supernova was of Type IIB
• The Expansion Asymmetry and Age of the Cassiopeia A Supernova Remnant
• Characterizing the non-thermal emission of Cas A
• The Kinematic and Plasma Properties of X-ray Knots in Cassiopeia A from the Chandra HETGS

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• Constraining the low-energy cosmic ray flux in the central molecular zone from MeV nuclear deexcitation line observations