Princeton University Astroplasmas Seminar

Abstract 1: The electron heating physics in collisionless shocks imprints upon micro-scale dissipation and waves seen in situ by heliospheric spacecraft, as well as X-ray emission from supernova remnants and galaxy clusters. How much do electrons heat, and how do they heat? We model low-beta heliospheric shocks with 1D and 2D fully-kinetic particle-in-cell simulations, taking fast Mach number 1–4 and total plasma beta 0.25. In the parameter space of quasi-perpendicular shocks (pre-shock magnetic field angles ~55–90 deg. from shock normal), we explore two regimes. For field angles near 90 deg., electrons are advected downstream by the magnetic field. Here, the parallel electric field of ion-scale oblique whistler waves—only captured in 2D—accelerates electrons into streams along the field, which then relax via two-stream-like instability. At more oblique field angles, subsonic electrons stream easily in and out of the shock. Here, electrons can gain energy from a cross-shock parallel electric potential jump and a secular potential rise along an oblique whistler wave train traveling just ahead of the shock. Post-shock electrons are colder than ions (Te/Ti ~ 0.1–1) in both regimes.

Abstract 2: The first photons from a supernova explosion emerge when the supernova’s radiation-mediated shock breaks out of the stellar surface, heralding an energetic transient event. These early shock-breakout photons carry invaluable information about the progenitor’s properties, its immediate environment, and the explosion mechanism. I will discuss this phenomenon in the context of weak stellar explosions (with explosion energy much smaller than the star's binding energy), and explain how the radiative dissipation of a blast wave sets a minimal energy scale below which shock acceleration cannot unbind any mass from the stellar envelope, and comment on implications regarding pre-supernova eruptions and early supernovae light curves. I will then present recent results regarding the bolometric light curve expected from the breakout of aspherical stellar explosions, and discuss the prospects of their discovery and characterization.