Monte-Carlo simulations of relativistic radiation mediated shocks: II. photon starved regime

Abstract

Radiation mediated shocks (RMS) play a key role in shaping the early emission observed in many transients. In most cases, e.g., shock breakout in supernovae, llGRBs and neutron star mergers, the upstream plasma is devoid of radiation, and the photons that ultimately reach the observer are generated predominantly inside and downstream of the shock. Predicting the observed spectrum requires detailed calculations of the shock structure and thermodynamic state that account properly for the shock microphysics. We present results of self-consistent Monte-Carlo simulations of photon-starved RMS, that yield the shock structure and emission for a broad range of shock velocities, from sub-relativistic (${\beta }_{sh}=0.1$) to highly relativistic (${\Gamma }_{sh}=20$). Our simulations confirm that in relativistic RMS the immediate downstream temperature is regulated by exponential pair creation, ranging from $50$ keV at ${\beta }_{sh}=0.5$ to $200$ keV at ${\Gamma }_{sh}=20$. At lower velocities the temperature becomes sensitive to the shock velocity, with $kT\sim 0.5$ keV at ${\beta }_{sh}=0.1$. We also confirm that in relativistic shocks the opacity is completely dominated by newly created pairs, which has important implications for the breakout physics. We find the transition to pair dominance to occur at ${\beta }_{sh}=0.5$ roughly. In all cases examined, the spectrum below the $\nu F_{\nu }$ peak has been found to be substantially softer than the Planck distribution. This has important implications for the optical emission in fast and relativistic breakouts, and their detection. The applications to GRB 060218 and GRB 170817A are discussed.

12 pages, 11 figures, accepted for publication in MNRAS

References in corpus (9)

• Illuminating Gravitational Waves: A Concordant Picture of Photons from a Neutron Star Merger
• Quasi-blackbody component and radiative efficiency of the prompt emission of gamma-ray bursts
• Very high efficiency photospheric emission in long duration gamma-ray bursts
• A unified picture for low-luminosity and long gamma-ray bursts based on the extended progenitor of llgrb 060218/SN 2006aj
• GRB170817A associated with GW170817: multifrequency observations and modeling of prompt gamma-ray emission
• Relativistic Radiation Mediated Shocks
• Shock Breakout in Type Ibc Supernovae and Application to GRB 060218/SN 2006aj
• Relativistic Photon Mediated Shocks
• Monte-Carlo simulations of relativistic radiation mediated shocks: I. photon rich regime

Cited by in corpus (10)

• Black hole to breakout: 3D GRMHD simulations of collapsar jets reveal a wide range of transients
• Blasts from the Past: Supernova Shock Breakouts among X-Ray Transients in the XMM-Newton Archive
• A global numerical model of the prompt emission in short gamma-ray bursts
• Monte-Carlo simulations of fast Newtonian and mildly relativistic shock breakout from a stellar wind
• Plasma kinetic effects in relativistic radiation mediated shocks
• The role of plasma instabilities in relativistic radiation mediated shocks: stability analysis and particle-in-cell simulations
• Cocoon shock breakout emission from binary neutron star mergers
• Magnetically driven coupling in relativistic radiation-mediated shocks
• An unexplored regime of shock breakout with a distinct spectral signature
• Anomalous coupling in radiation mediated shocks}