Turbulence and Magnetic Field Amplification in Supernova Remnants: Interactions Between a Strong Shock Wave and Multiphase Interstellar Medium

Abstract

We examine MHD simulations of the propagation of a strong shock wave through the interstellar two-phase medium composed of small-scale cloudlets and diffuse warm neutral medium in two-dimensional geometry. The pre-shock two-phase medium is provided as a natural consequence of the thermal instability that is expected to be ubiquitous in the interstellar medium. We show that the shock-compressed shell becomes turbulent owing to the preshock density inhomogeneity and magnetic field amplification takes place in the shell. The maximum field strength is determined by the condition that plasma β ∼ 1, which gives the field strength on the order of 1 mG in the case of shock velocity ∼ 10 3 km s −1 . The strongly magnetized region shows filamentary and knot-like structures in two-dimensional simulations. The spatial scale of the regions with magnetic field of ∼1 mG in our simulation is roughly 0.05 pc which is comparable to the spatial scale of the X-ray hot spots recently discovered in supernova remnants where the magnetic field strength is indicated to be amplified up to the order of 1 mG. This result may also suggest that the turbulent region with locally strong magnetic field is expected to be spread out in the region with frequent supernova explosions, such as in the Galactic center and starburst galaxies.

Diffusive Shock Acceleration Simulations of Radio Relics

“…Theoretical studies have shown that efficient magnetic field amplification via resonant and nonresonant wave-particle interactions is an integral part of DSA at strong shocks (Lucek & Bell 2000;Bell 2004). In addition, magnetic fields can be amplified by turbulent motions behind shocks (Giacalone & Jokipii 2007;Inoue et al 2009). Yet, these plasma processes are complex and their roles are not yet entirely certain, especially at weak shocks.…”

On the structure of the turbulent interstellar clouds

“…This includes 1D calculations (Hennebelle & Pérault 1999;Koyama & Inutsuka 2000;Sánchez-Salcedo et al 2002;Inoue et al 2006), 2D calculations (Koyama & Inutsuka 2002;Audit & Hennebelle 2005;Heitsch et al 2005Heitsch et al , 2006 and 3D calculations (Kritsuk & Norman 2002;Gazol et al 2005;Vázquez-Semadeni et al 2006). The influence of the magnetic field on the dynamics of a thermally bistable flow has been investigated by Hennebelle & Pérault (2000), Piontek & Ostriker (2004, de Avillez & Breitschwerdt (2005), Hennebelle & Passot (2006), and more recently by Inoue & Inutsuka (2008), , Heitsch et al (2009), Inoue et al (2009) and Gazol et al (2009).…”

Magnetic Field Amplification in Supernova Remnants

“…More generally, turbulence is believed to be an efficient agent to amplify magnetic fields via the turbulent dynamo (Kazantsev 1968;Kulsrud & Anderson 1992), which has also been invoked for explaining both the preshock (Beresnyak, Jones, & Lazarian 2009, hereafter BJL09;Drury & Downes 2012;del Valle et al 2016) and postshock (Balsara et al 2001;Giacalone & Jokipii 2007;Inoue et al 2009;Guo et al 2012;Fraschetti 2013;Ji et al 2016) magnetic fields. As turbulence is induced by the interaction between SNR shocks and interstellar turbulent density fluctuations, the turbulent dynamo is inevitable in SNRs with the turbulent kinetic energy dominating over the pre-existing magnetic energy.…”