Shock waves produce relativistic particles via the diffusive shock acceleration (DSA) mechanism. Among various circumstances, fast acceleration has been expected for perpendicular shocks. We investigate the acceleration time and the energy spectrum of particles accelerated at a perpendicular shock. In our model, the upstream perpendicular magnetic field has no fluctuation, and the downstream region is highly turbulent. Then, the particle motion is the gyration in the upstream region and Bohm-like diffusion downstream. Under this situation, we derive an analytical form of the acceleration time. Using test particle simulations, the validity of our formula is verified. In addition, the energy spectrum of particles is the same as those predicted by standard DSA. Therefore, the presently proposed mechanism simultaneously realizes the rapid acceleration and the canonical spectrum, dN/dp ∝ p −2, even if there is no upstream magnetic amplification.

No abstract

We investigate the maximum energy limited by the escape from a perpendicular shock region of a spherical shock in the interstellar medium (ISM), and the size of the rapid acceleration region. The perpendicular shock of supernova remnants (SNRs) has been expected to be PeVatrons without a magnetic field amplification in the upstream region. We perform test particle simulations, showing that the escape-limited maximum energy in the perpendicular shock is about a few 10 TeV for the typical type Ia SNRs. In addition, we show that, in the free expansion phase, the rapid perpendicular shock acceleration realizes in about 20% area of the whole shock surface, which is much larger than the superluminal shock region.

No abstract

We investigate the acceleration process of particles in core-collapse supernova remnants (SNRs) propagating in the circumstellar medium with the Parker-spiral magnetic field, current sheet, and wind termination shock (WTS). Wolf-Rayet (WR) stars are considered in this work as progenitors of supernovae. Test particle simulations are performed to reveal the particle motion between the SNR shock and WTS and attainable maximum energy without magnetic field amplification in the upstream region, where the magnetic field strength and rotation period expected from observations of WR stars are used. We show that particles can experience the cyclic motion between the SNR shock and WTS until the SNR shock collides with the WTS. Particles are accelerated at the SNR shock and WTS again and again and the attainable maximum energy can exceed the maximum energy limited by escape from core-collapse SNRs.