Numerical Simulations of Supernova Remnant Evolution in a Cloudy Interstellar Medium

Abstract

The mixed morphology class of supernova remnants has centrally peaked X-ray emission along with a shell-like morphology in radio emission. White & Long proposed that these remnants are evolving in a cloudy medium wherein the clouds are evaporated via thermal conduction once being overrun by the expanding shock. Their analytical model made detailed predictions regarding temperature, density and emission profiles as well as shock evolution. We present numerical hydrodynamical models in 2D and 3D including thermal conduction, testing the White & Long model and presenting results for the evolution and emission from remnants evolving in a cloudy medium. We find that, while certain general results of the White & Long model hold, such as the way the remnants expand and the flattening of the X-ray surface brightness distribution, in detail there are substantial differences. In particular we find that the X-ray luminosity is dominated by emission from shocked cloud gas early on, leading to a bright peak which then declines and flattens as evaporation becomes more important. In addition, the effects of thermal conduction on the intercloud gas, which is not included in the White & Long model, are important and lead to further flattening of the X-ray brightness profile as well as lower X-ray emission temperatures.

A new numerical code for hydrodynamical 3D simulations of supernova remnants

“…It causes the density of hot gas to increase by the mass loss from clumps, as the thermal conduction effectively smooths out the temperature and density inhomogeneities. Slavin et al (2017) included thermal conduction in their simulations and conclude that (a) the evaporation does not affect the Sedov expansion law R ∝ t 2/5 and (b) the evaporation timescale increases proportionally to the remnant age. This means that the clumps far away from the SNR center will not be efficiently evaporated, as pointed out also by McKee and Ostriker (1977).…”

“…A better understanding of the SNR-ISM interaction will enable the use of SNRs as proxies for the ISM structure. For recent studies in this direction see Orlando et al (2019), Zhang and Chevalier (2019), Yu et al (2015) and Slavin et al (2017).…”

“…The simulations of SNRs are carried out in both uniform and inhomogeneous medium. In the case of uniform medium, the density is set to ρ 0 = 0.25 H cm −3 with a temperature T 0 = 10 4 K. These numbers are typical values for warm ISM and are also used in Slavin et al (2017) who simulated supernova remnants in a cloudy environment. Since the medium is set to have no momentum and kinetic energy, all energy is the internal (pressure energy).…”

“…Since the medium is set to have no momentum and kinetic energy, all energy is the internal (pressure energy). Unlike Slavin et al (2017), who created a cloudy medium by randomly distributing the homogeneous spherical clumps of the same higher density (25 H cm −3 ), but of different sizes, we model the molecular cloud by distributing the density as a hierarchical structure, creating the smooth fractal distribution of very different densities. Another way of modeling the inhomogeneous medium is given in Yu et al (2015) in an MHD study of SNR expanding in a turbulent plasma with a relatively small amplitude of turbulence.…”

Eigenvalue Method for NEI Unit in FLASH Code

“…6). The simulation is set to be a SNR explosion going through some spherical dense clouds (in 2D; Slavin et al 2017). The ionization and recombination appear in the shock front and around the clouds.…”