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Title: The spectrum of a fast shock breakout from a stellar wind
Authors: Ioka, Kunihito  kyouindb  KAKEN_id  orcid (unconfirmed)
Levinson, Amir
Nakar, Ehud
Author's alias: 井岡, 邦仁
Keywords: radiation: dynamics
shock waves
gamma-ray burst: general
supernovae: general
stars: Wolf–Rayet
Issue Date: Apr-2019
Publisher: Oxford University Press (OUP)
Journal title: Monthly Notices of the Royal Astronomical Society
Volume: 484
Issue: 3
Start page: 3502
End page: 3509
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.
Rights: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2019 Kunihito Ioka, Amir Levinson, Ehud Nakar. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
DOI(Published Version): 10.1093/mnras/stz270
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