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 interactingwith circumstellar material. The dense layer behind high Mach number M ≫ 1 radiative shocks is susceptible to thin-shell instabilities, creating a 'corrugated' shock interface. We present 2D and 3D hydrodynamical simulations of optically thin radiative shocks to study their thermal radiation and acceleration of non-thermal relativistic ions.We employ amoving-mesh code and a specialized numerical technique to eliminate artificial heat conduction across grid cells. The fraction of the shock's luminosity Ltot radiated at X-ray temperatures kTsh ≈ (3/16)μmpv2sh expected from a 1D analysis is suppressed by a factor L(> Tsh/3)/Ltot ≈ 4.5/M4/3 for M ≈ 4-36. This suppression results in part from weak shocks driven into underpressured 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 εnth ~ 0.005-0.02 for M ≈ 12-36, in agreement with modelling of the gamma-ray nova ASASSN-16ma.
Bibliographical noteFunding Information:
ES and BDM are supported through the NSF grant AST-1615084, NASA Fermi Guest Investigator Program grants NNX16AR73G and 80NSSC17K0501; and through Hubble Space Telescope Guest Investigator Program grant HST-AR-15041.001-A. We thank Dami-ano Caprioli, John Raymond, and Lorenzo Sironi for helpful comments and conversations. We acknowledge computing resources from Columbia University’s Shared Research Computing Facility project, which is supported by NIH Research Facility Improvement Grant 1G20RR030893-01, and associated funds from the New York State Empire State Development, Division of Science Technology and Innovation Contract C090171, both awarded 2010 April 15.
© 2018 The Author(s). Published by Oxford University Press on behalf of The Royal Astronomical Society.
- Radiation: dynamics
- Shock waves
- Stars: novae
- Stars: supernovae: general
- X-rays: bursts