Cosmic ray acceleration in magnetic circumstellar bubbles

Abstract

We consider the diffusive shock acceleration in interstellar bubbles created by powerful stellar winds of supernova progenitors. Under the moderate stellar wind magnetization the bubbles are filled by the strongly magnetized low density gas. It is shown that the maximum energy of particles accelerated in this environment can exceed the "knee" energy in the observable cosmic ray spectrum.

Wind nebulae and supernova remnants of very massive stars

“…A number of numerical simulations calculating the acceleration and diffusion of cosmic rays in static stellar-wind/bow-shock environments of massive stars have been performed (del Valle et al 2013(del Valle et al , 2015del Valle & Pohl 2018), and speculative predictions were announced for the Bubble nebula, a runaway OB star moving through dense molecular gas (Green et al 2019). Particle acceleration and the production of non-thermal emission in the surroundings of pre-supernova (runaway) massive stars are expected to arise from processes similar to those operating in young supernova remnants (Reynolds 2011), albeit with smaller efficiency (Voelk & Forman 1982;Zirakashvili & Ptuskin 2018). Per object, circumstellar cosmic-ray feedback of high-mass stars is of lower importance in the Galactic energy budget compare to other non-thermal-emitting objects such as supernova remnants (Seo et al 2018;Rangelov et al 2019) or colliding winds in binaries (Benaglia & Romero 2003;De Becker et al 2006;Reimer et al 2006;De Becker & Raucq 2013).…”

Revealing a peculiar supernova remnant G106.3+2.7 as a petaelectronvolt proton accelerator with X-ray observations

“…This scenario is corroborated by the presence of a dense molecular cloud that spatially coincides with both the tail region and the centroid of the gamma-ray emissions. On the other hand, from a theoretical point of view, SNRs expanding in stellar wind cavities have been suggested as promising accelerators of PeV protons 42 , 43 because a quasi-perpendicular SNR shock may form in this environment, with an acceleration efficiency comparable with that in the Bohm limit (i.e., ). These various arguments consistently support that the tail region of SNR G106.3+2.7 is likely a Galactic proton PeVatron.…”

Role of the radiative stage for cosmic ray acceleration in SNRs

“…So the maximum energies determined by CR streaming instability are not higher than 100 TeV in SNRs considered. Higher energies can be reached for SNRs shocks propagating in rarefied bubbles created by Type Ib/c supernova progenitors where the medium is prepared for the efficient DSA (Zirakashvili & Ptuskin 2018b or in dense progenitor winds of IIn Type SNRs (Zirakashvili & Ptuskin 2016b).…”