Non-linear model of particle acceleration at colliding shock flows

Abstract

Powerful stellar winds and supernova explosions with intense energy release in the form of strong shock waves can convert a sizeable part of the kinetic energy release into energetic particles. The starforming regions are argued as a favorable site of energetic particle acceleration and could be efficient sources of nonthermal emission. We present here a non-linear time-dependent model of particle acceleration in the vicinity of two closely approaching fast magnetohydrodynamic (MHD) shocks. Such MHD flows are expected to occur in rich young stellar cluster where a supernova is exploding in the vicinity of a strong stellar wind of a nearby massive star. We find that the spectrum of the high energy particles accelerated at the stage of two closely approaching shocks can be harder than that formed at a forward shock of an isolated supernova remnant. The presented method can be applied to model particle acceleration in a variety of systems with colliding MHD flows.

Nonthermal particles and photons in starburst regions and superbubbles

“…Other possible PeV neutrino sources were proposed recently including semirelativistic hypernova remnants by Liu et al (2014) and shock acceleration of PeV CR particles in massive galaxy mergers or collisions by Kashiyama and Mészáros (2014). In the case of massive galaxy mergers/collisions CR acceleration in colliding shock flows modeled by Bykov et al (2013b) may play a role.…”

“…On the other hand, they found that a model with proton acceleration in the cluster's supernova explosion(s) with subsequent interaction with the surrounding molecular material may explain both the GeV and TeV emission, but requires a very high energy input in protons and rather a slow diffusion. In §6.3 we shall discuss in some detail another potentially very fast and efficient mechanism of particle acceleration in colliding shock flows suggested by Bykov et al (2013b). The colliding shock flow occurs in a compact cluster where a strong expanding supernova shock is approaching a fast wind of a nearby massive star or collides with the supersonic wind produced by the compact cluster.…”

“…It is instructive to note that the simulated system at some evolutional stage (of about some thousands of years duration) may become a very efficient accelerator of energetic particles. It may transfer about a half of the kinetic ram pressure into the energetic non-thermal particles as demonstrated within the one-dimensional non-linear kinetic model of Bykov et al (2013b). A 2D hydrodynamical model of the temporal evolution of an aspherical circumstellar bubble created by two massive stars of 25 M and 40 M separated by 16 pc in a cold 20 cm −3 medium, which included the stage of supernova explosion was presented by van Marle et al (2012).…”

“…Such particles are subject to Fermi I acceleration. Right Panel: The spatial distribution (gray scale) and differential spectra Φ(p) = dN/dp(p) of the accelerated high energy particles taken at different evolution stages simulated with a non-linear kinetic model by Bykov et al (2013b). The panels from top to bottom are corresponding to four different distances between the approaching shocks 0.6, 0.5, 0.3, 0.1 pc respectively.…”

“…9 shows the results of non-linear time-dependent modeling of energetic particle distribution in the vicinity of two closely approaching fast plane-parallel MHD shocks at different distances between the shocks (from the top to bottom) as it was simulated by Bykov et al (2013b). The gray scale panels in Fig.…”