The Spectrum of a Fast Shock Breakout from a Stellar Wind

Abstract

The breakout of a fast ($>0.1c$), yet sub-relativistic shock from a thick stellar wind is expected to produce a pulse of X-rays with a rise time of seconds to hours. Here, we construct a semi-analytic model for the breakout of a sub-relativistic, radiation-mediated shock from a thick stellar wind, and use it to compute the spectrum of the breakout emission. The model incorporates photon escape through the finite optical depth wind, assuming a diffusion approximation and a quasi-steady evolution of the shock structure during the breakout phase. We find that in sufficiently fast shocks, for which the breakout velocity exceeds about $0.1c$, the time-integrated spectrum of the breakout pulse is non-thermal, and the time-resolved temperature is expected to exhibit substantial decrease (roughly by one order of magnitude) during breakout, when the flux is still rising, because of the photon generation by the shock compression associated with the photon escape. We also derive a closure relation between the breakout duration, peak luminosity, and characteristic temperature that can be used to test whether an observed X-ray flare is consistent with being associated with a sub-relativistic shock breakout from a thick stellar wind or not. We also discuss implications of the spectral softening for a possible breakout event XRT 080109/SN 2008D.

8 pages, 8 figures, accepted for publication in MNRAS

References in corpus (14)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• Multi-messenger Observations of a Binary Neutron Star Merger
• Illuminating Gravitational Waves: A Concordant Picture of Photons from a Neutron Star Merger
• Confined Dense Circumstellar Material Surrounding a Regular Type II Supernova: The Unique Flash-Spectroscopy Event of SN 2013fs
• A Wolf-Rayet-like progenitor of supernova SN 2013cu from spectral observations of a wind
• From Shock Breakout to Peak and Beyond: Extensive Panchromatic Observations of the Type Ib Supernova 2008D associated with Swift X-ray Transient 080109
• The metamorphosis of Supernova SN2008D/XRF080109: a link between Supernovae and GRBs/Hypernovae
• A cocoon shock breakout as the origin of the $\gamma$-ray emission in GW170817
• The delay of shock breakout due to circumstellar material seen in most Type II Supernovae
• From $\gamma$ to Radio - The Electromagnetic Counterpart of GW 170817
• Nonthermal gamma-ray and X-ray flashes from shock breakout in gamma-ray bursts/supernovae
• SN 2008D: A Wolf-Rayet explosion through a thick wind
• Monte-Carlo simulations of relativistic radiation mediated shocks: I. photon rich regime
• X-rays, gamma-rays and neutrinos from collisoinless shocks in supernova wind breakouts

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• Monte-Carlo simulations of relativistic radiation mediated shocks: II. photon starved regime
• Plasma kinetic effects in relativistic radiation mediated shocks
• GW170817 event rules out general relativity in favor of vector gravity
• Cocoon shock breakout emission from binary neutron star mergers
• An unexplored regime of shock breakout with a distinct spectral signature
• Radiation-mediated shocks in gamma-ray bursts: spectral evolution