English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Giant radio relics in the outskirts of galaxy clusters are known to be lit upby the relativistic electrons produced via diffusive shock acceleration (DSA)in shocks with low sonic Mach numbers, $M_{\rm s}\lesssim3$. The particleacceleration at these collisionless shocks critically depends on the kineticplasma processes that govern the injection to DSA. Here, we study thepreacceleration of suprathermal electrons in weak, quasi-perpendicular($Q_\perp$) shocks in the hot, high-$\beta$ ($\beta = P_{\rm gas}/P_{\rm B}$)intracluster medium (ICM) through two-dimensional particle-in-cell simulations.\citet{guo2014a,guo2014b} showed that in high-$\beta$ $Q_\perp$-shocks, some ofincoming electrons could be reflected upstream and gain energy via shock driftacceleration (SDA). The temperature anisotropy due to the SDA-energizedelectrons then induces the electron firehose instability (EFI), and obliquewaves are generated, leading to a Fermi-like process and multiple cycles of SDAin the preshock region. We find that such electron preacceleration is effectiveonly in shocks above a critical Mach number $M_{\rm ef}^*\approx2.3$. Thismeans that in ICM plasmas, $Q_\perp$-shocks with $M_{\rm s}\lesssim2.3$ may notefficiently accelerate electrons. We also find that even in $Q_\perp$-shockswith $M_{\rm s}\gtrsim2.3$, electrons may not reach high enough energies to beinjected to the full Fermi-I process of DSA, because long-wavelength waves arenot developed via the EFI alone. Our results indicate that additional electronpreaccelerations are required for DSA in ICM shocks, and the presence of fossilrelativistic electrons in the shock upstream region may be necessary to explainobserved radio relics.

Electron Preacceleration in Weak Quasi-perpendicular Shocks in High-beta Intracluster Medium