Laboratory Observation of Radiative Shock Deceleration and Application to SN 1987A

Abstract

The first laboratory evidence of a radiative shock (RS) decelerating during its free expansion phase in an optically thick medium is presented. A shock is generated in a multilayer solid target under the irradiation of a high-power laser at the GEKKO XII laser facility. The rear surface of the target is connected to a gas cell filled with Xe. Upon breakout, an RS, characterized by low Boltzmann number Bo ≪ 1 and Mihalas number R ≈ 10, is generated. Experimental results reveal that radiative losses through the radiative precursor cause the shock to lose energy and decelerate. A model is developed that describes the shock propagation as a function of time. The model is in agreement with both numerical simulations and experimental results. These results have tremendous consequences for astrophysical systems, such as SN 1987A, where radiative deceleration may play a role in the formation of the observed hotspots in the circumstellar ring.

Calculating the temperature of strongly radiative shocks

“…The conditions considered here can be thought of as those encountered upon the formation of the radiative shock, on timescales shorter than those associated with the growth of any instabilities. Previous experiments in the field show that said shocks may safely be considered stable on the timescale of several nanoseconds 26,30 .…”

“…Radiative effects such as the existence of shock precursor regions 27,28 as well as velocity domain oscillations 29 have been observed. Recent experiments, with larger radiation energies, have shown other effects, less thoroughly discussed in the literature, such as the deceleration due to radiative losses 30 . However, there is still uncertainty surrounding the temperature of radiative shocks in such experiments due to the paucity of directly experimentally measured data (see for example the most recent experiments in the field 30,31 which do not make any attempt to measure this parameter).…”

“…Recent experiments, with larger radiation energies, have shown other effects, less thoroughly discussed in the literature, such as the deceleration due to radiative losses 30 . However, there is still uncertainty surrounding the temperature of radiative shocks in such experiments due to the paucity of directly experimentally measured data (see for example the most recent experiments in the field 30,31 which do not make any attempt to measure this parameter). This represents a significant problem, as the temperature of a radiative shock is of prime importance in determining the extent to which the shock is in fact radiative.…”

“…This method therefore cannot be used to determine the temperature of shocks, one might suspect to be radiative in nature. Indeed, laboratory experiments have already showed that radiation has a significant impact on shock speed and that a modified version of the Rankine-Hugoniot jump conditions are necessary 30 , and this comes as no surprise.…”

First radiative shock experiments on the SG-II laser

“…Radiative effects increase with the shock speed due to stronger post-shock heating and, in a first approximation for typical experimental conditions, shocks [3] and applications to astrophysics [4] . In particular, recent experiments have looked at the interaction of a pistondriven shock with an obstacle [5,6] . However, several issues have led to difficulties making a complete bridge between simulations and experiments, for instance, the question of opacity for heavy gases (e.g., xenon) or the nature of the rise of instabilities and the role played by radiation.…”