Radiative shocks , behind which gas cools faster than the dynamical time , play a key role in many astrophysical transients , including classical novae and young supernovae interacting with circumstellar material .
The dense layer behind high Mach number \mathcal { M } \gg 1 radiative shocks is susceptible to thin-shell instabilities , creating a ‘ ‘ corrugated '' shock interface .
We present two and three-dimensional hydrodynamical simulations of optically-thin radiative shocks to study their thermal radiation and acceleration of non-thermal relativistic ions .
We employ a moving-mesh code and a specialized numerical technique to eliminate artificial heat conduction across grid cells .
The fraction of the shock ’ s luminosity L _ { tot } radiated at X-ray temperatures kT _ { sh } \approx ( 3 / 16 ) \mu m _ { p } v _ { sh } ^ { 2 } expected from a one-dimensional analysis is suppressed by a factor L ( > T _ { sh } / 3 ) / L _ { tot } \approx 4.5 / \mathcal { M } ^ { 4 / 3 } for \mathcal { M } \approx 4 - 36 .
This suppression results in part from weak shocks driven into under-pressured cold filaments by hot shocked gas , which sap thermal energy from the latter faster than it is radiated .
Combining particle-in-cell simulation results for diffusive shock acceleration with the inclination angle distribution across the shock ( relative to an upstream magnetic field in the shock plane - the expected geometry for transient outflows ) , we predict the efficiency and energy spectrum of ion acceleration .
Though negligible acceleration is predicted for adiabatic shocks , the corrugated shock front enables local regions to satisfy the quasi-parallel magnetic field geometry required for efficient acceleration , resulting in an average acceleration efficiency of \epsilon _ { nth } \sim 0.005 - 0.02 for \mathcal { M } \approx 12 - 36 , in agreement with modeling of the gamma-ray nova ASASSN-16ma .