Relativistic shock breakout from a stellar wind

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Abstract

We construct an analytic model for the breakout of a relativistic radiation mediated shock from a stellar wind, and exploit it to calculate the observational diagnostics of the breakout signal. The model accounts for photon escape through the finite optical depth wind, and treats the fraction of downstream photons escaping to infinity as an adiabatic parameter that evolves in a quasi-steady manner. It is shown that the shock is mediated by radiation even when a large fraction of the downstream photons escape, owing to self-generation and adjustment of opacity through accelerated pair creation. Relativistic breakout occurs at radii at which the total optical depth of the wind ahead of the shock is ~(me/mpsh, provided that the local shock Lorentz factor Γsh exceeds unity at this location. Otherwise the breakout occurs in the Newtonian regime. A relativistic breakout is expected in a highly energetic spherical explosion (1052-1053 erg) of aWolf-Rayet star, or in cases where a smaller amount of energy (~1051 erg) is deposited by a jet in the outer layers of the star. The properties of the emission observed in such explosions during the relativistic breakout are derived. We find that for typical parameters about 1048 ergs are radiated in the form of MeV gamma-rays over a duration that can range from a fraction of a second to an hour. Such a signal may be detectable out to 10-100 Mpc by current gamma-ray satellites.

Original languageEnglish
Pages (from-to)5453-5463
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Volume476
Issue number4
DOIs
StatePublished - 1 Jun 2018

Keywords

  • Gamma-ray burst: general
  • Radiation: dynamics
  • Relativistic processes
  • Shock waves
  • Supernovae: general

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