Recently, the GeV–sub-PeV spectrum of supernova remnant (SNR) Cassiopeia A (Cas A), one of the youngest and most well-studied SNRs in our Galaxy, has been updated by observations from Fermi-LAT and LHAASO. We revisit Cas A with our previous shell-plus-jet asymmetric model and investigate its particle acceleration ability. The broadband fitting results suggest that the double-peaked gamma-ray spectrum can be well attributed to proton-proton (PP) collisions and inverse Compton scattering within the SNR shell, while the synchrotron emission from a jet component with velocity of $\sim 0.1c$ can account for the hard x-ray emission up to 220 keV. Furthermore, the PP collisions in the jet can produce a sub-PeV emission, but constrained by the LHAASO-KM2A limit to a flux below $\sim 1\times {10}^{-14}\mathrm{erg}/({\mathrm{cm}}^2\mathrm{s})$ at 100 TeV. The energy of accelerated protons in the jet of Cas A could be up to $5\times {10}^{47}\mathrm{erg}$, which, assuming that the PeV cosmic ray distribution is clumpy in the Galaxy with the clump size comparable to the thickness of the Galactic plane, derives a proton flux consistent with the observed one at 1 PeV, implying that the Cas A-like SNRs can still be PeVatrons in the Galaxy. It is encouraging for LHAASO and future telescopes to detect or constrain the Cas A spectrum above 100 TeV more precisely.

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• Cosmic ray acceleration
• Cosmic ray sources
• Cosmic rays & astroparticles
• Supernova remnants