We briefly discuss models of energetic particle acceleration by supernova shock in active starforming regions at different stages of their evolution. Strong shocks may strongly amplify magnetic fields due to cosmic ray driven instabilities. We discuss the magnetic field amplification emphasizing the role of the long-wavelength instabilities. Supernova shock propagating in the vicinity of a powerful stellar wind in a young stellar cluster is argued to increase the maximal CR energies at a given evolution stage of supernova remnant (SNR) and can convert a sizeable fraction of the kinetic energy release into energetic particles.
The observed spectra of Galactic cosmic rays (CRs) are shaped by two basic processesthe acceleration in the sources and the subsequent propagation in cosmic magnetic fields and radiation fields. A transition from galactic to extragalactic cosmic rays is expected to occur somewhere between 10 17 eV and 10 19 eV (e.g. Hillas, 2005;Aharonian et al., 2011). A preponderance of evidence suggests that the particle acceleration mechanism most likely responsible is diffusive shock acceleration (DSA) (e.g., Blandford & Eichler, 1987;Jones & Ellison, 1991;Malkov & Drury, 2001).
An important question for DSA and CR origin has always centered around the maximum particle energy a given shock can produce. For a shock of a given size, age, and magnetic field geometry, the maximum CR Send offprint requests to: A.M. Bykov energy depends mainly on the power in the longest wavelength turbulence. The weakly anisotropic distribution of accelerated particles, i.e., CRs is considered in § 2 as an agent producing this turbulence in a symbiotic relationship where the magnetic turbulence required to accelerate the CRs is created by the accelerated CRs themselves.
Other important issue of the high energy CR acceleration models is the environment where the supernova exploded. Some models of CRs acceleration by SNRs in active star forming regions are briefly discussed in § 3. OB-associations and young globular clusters are observed both in the Milky Way and LMC. The study of the stellar content of the galactic object Cygnus OB2 by Knödlseder (2000) have revealed that the number of OB member stars can be estimated as large as 2600 ± 400, while the number of O stars amounts to 120 ± 20. The high number of stellar X-ray sources detected with Chandra by Wright & Drake (2009) confirmed the status of Cygnus OB2 as one of the most massive SFRs in the Milky Way. Given the apparently compact size of Cygnus OB2 one may expect a number of massive stars with strong winds to be in a close proximity with less than 10 pc separation in addition to the well known colliding-wind binaries that are expected to be particle accelerators (e.g. Eichler & Usov, 1993). Another very compact young stellar cluster Westerlund 2 containing more than dozen O stars was found in the Carina region with estimated age to be younger than 4 Myrs, so the most massive stars are expected to explode there within the next few Myrs. OB associations with supernova explosions are creating superbubbles (SBs). Bamba et al. (2004) discovered both thermal and nonthermal X-rays from the shells of the SB 30 Dor C in the LMC. The X-ray morphology was reported as a nearly circular shell with a radius of 40 pc, which is bright on the northern and western sides. Maddox et al. (2009) analyzed Suzaku observations of the SB around the OB association LH9 in the HII complex N11 in the Large Magellanic Cloud. Their X-ray spectral analysis revealed that the hard X-ray emission (> 2 keV) requires a hard nonthermal power-law component. The energy budget analysis for N11 using the known stellar content of LH9 indicated that the observed thermal and kinetic energy in the SB is only half of the expected mechanical energy injected by stars, consistent with the expectation of SB models with efficient CR acceleration (e.g. Bykov, 2001;Butt & Bykov, 2008). Diffuse X-ray emission was detected from many sites of massive star formation: the Carina Nebula, M17, 30 Doradus, NGC 3576, NGC 3603, and others (e.g. Townsley et al., 2011). The H.E.S.S. telescope detected highenergy gamma rays from starburst galaxy NGC 253 supporting the ideas of efficient CR acceleration in active starforming regions (Acero, 2009).
Fast and efficient CR acceleration by Fermi mechanism requires that particles are multi-ply scattered by magnetic fluctuations in the acceleration source (e.g. shock). The magnitude of the required magnetic fluctuations is substantially higher than the ambient magnetic turbulence forcing a bootstrap scenario where the accelerated particles amplify the turbulence required for their acceleration. The study of turbulence generation associated with CRs and DSA has a long history. Magnetic field amplification due to the resonant cosmic-ray streaming instability was studied in the context of galactic cosmic-ray origin and propagation since the 1960s (see e.g. Kulsrud & Cesarsky, 1971;Wentzel, 1974;Achterberg, 1981;Berezinskii et al., 1990;Zweibel, 2003).
It was proposed by Bell (1978) as a source of magnetic turbulence in the test particle DSA scenario, and nonlinear models of DSA including CR-driven instabilities and magnetic field amplification were investigated by Bell (2004); Amato & Blasi (2006); Zirakashvili & Ptuskin (2008), Vladimirov et al. (2008Vladimirov et al. ( , 2009) ) and Reville et al. (2009).
It is instructive to summarize the growth rates for magnetic instabilities that the quasilinear theory predicts for weakly anisotropic CR distributions of the form
where θ -particle pitch-angle, µ = co
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