Interstellar medium structure and the slope of the radio Σ–Drelation of supernova remnants

Abstract

We analyze the influence of fractal structure of the interstellar matter (ISM) density on the parameter values for the radio surface brightness to diameter (Σ − D) relation for supernovae remnants (SNRs). We model a dense ISM as a molecular cloud with fractal density structure. SNRs are modelled as spheres of different radius scattered in the modelled ISM. The surface brightness of the SNRs is calculated from the simple relation Σ ∝ ρ 0.5 D −3.5 and also from the parametrized more general form Σ ∝ ρ η D −β0 . Our results demonstrate that empirical Σ − D slopes that are steeper than the ones derived from theory, might be partly explained with the fractal structure of the ambient medium into which SNRs expand. The slope of the Σ − D relation steepens if the density of the regions where SNRs are formed is higher. The simple geometrical effects combined with the fractal structure of the ISM can contribute to a steeper empirical Σ − D slopes, especially for older remnants, and this is more pronounced if Σ has a stronger dependence on ambient density.

Statistical Analysis of Supernova Remnants in the Large Magellanic Cloud

“…As described in Vukotić et al (2014) this has many advantages compared to the standard fit parameters based analysis since all the information from the data sample is preserved and not just projected onto the parameters of the fit line. We calculated the Σ − D PDF using kernel density smoothing described in Sec- Kostić et al 2016). Further analysis and theoretical work is required on this matter in addition to thorough surveys.…”

“…Consequently, depending on the progenitor type (ambient density), SNRs should form a broad band corresponding to evolutionary tracks in Σ − D plane. The dependence of Σ − D evolution on ambient density is further explored in Kostić et al (2016). Under the assumption that SNRs expanding in an ambient medium of higher density have higher Σ, they argued in favour of the dependence of the slope of the Σ − D relation on the fractal properties of the ISM density distribution in the areas crowded with molecular clouds.…”

Discovery of a new supernova remnant G21.8−3.0

“…Note that distances estimated from the Σ-D relation have an uncertainty as large as 35% or more due to several facts, e.g. the intrinsic properties of SNRs, the environments where SNRs evolve, and the selection effects of the calibration sample (Green 1984;Pavlović et al 2013;Kostić et al 2016). We therefore emphasise that the distance of G21.8−3.0 is still an open issue, which may be settled by new CO/H i data with higher angular resolution and sensitivity or future finding of 1720-MHz OH masers due to SNR-MC interactions, or even using red clump stars or dust extinction (e.g.…”

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

“…Apart from the uniform medium, the SNR simulations will be run in inhomogeneous medium that resembles the molecular clouds. Here, we present a model of such medium which is based on the work of Elmegreen (1997) and developed for application on SNRs in Kostić et al (2016). As the researches from past few decades indicate, the interstellar medium, especially molecular clouds, show some kind of fractal structure (Elmegreen and Falgarone 1996, Stutzki et al 1998, Blitz and Williams 1999).…”

“…where D f is called the fractal dimension. This quantity, and its possible influence on hydrodynamical evolution of supernova remnants, is discussed in more details in Kostić et al (2016) and references therein. Shortly, it is a measure of fractal object's space-filling ability and characterizes the scaling ratio between the structure and its substructures.…”