Time-Dependent Spectra of Cosmic Rays Escaping from Type Ia and Core-Collapse Supernova Remnants

摘要

Supernova Remnants (SNRs) are thought to be the main sources of Galactic cosmic rays (CRs) up to the ”knee”. The soft CR spectrum observed at Earth, and also soft gamma-ray spectra observed from a number of SNRs interacting with molecular clouds (MCs), challenge current theories of non-linear particle acceleration that predict harder slopes. However, one should keep in mind that the CRs at Earth as well as the CRs producing gamma-rays by interaction with MCs surrounding SNRs are actually particles that escaped from the parent SNRs. During the SNR evolution the bulk of the CRs is confined within the SNR shell. The highest-energy particles leave the system continuously, while the rest of the adiabatically cooled particles are released when the SNR has sufficiently expanded and slowed down to the point that the magnetic field (MF) at the shock is no longer able to confine them. We study how the spectrum of escaped particles depends on the time-dependent acceleration history in young type-Ia and core-collapse SNRs by combining numerical simulations of SNR evolution with a solution of the CR transport equation in test-particle mode. Having explored the significance of particles accelerated at the reverse shock (RS) for the emission from the SNR, we calculate the time-dependent gamma-ray spectra from MCs illuminated by the escaping CRs.