Cosmic-Ray Acceleration from Supernova Ejecta in Superbubbles

Abstract

We suggest that the cosmic rays are accelerated primarily out of the supernova ejecta-enriched matter in the interiors of superbubbles. These hot, low-density superbubbles, which reach dimensions of several hundred parsecs, are generated by the winds and ejecta of supernova explosions of massive stars formed in giant molecular cloud OB associations that last for tens of megayears. Since these bubbles expand with shell velocities that are much faster than the dispersion velocities of the O and B star progenitors of the supernovae that power the bubbles, the bulk of the supernovae occur in their cores. The expanding remnants of each of these supernovae fill only less than 1% of this core before they have slowed to sonic velocities. Thus, the bulk of these supernovae remnants, together with their metal-rich grain and gas ejecta and their cosmic-ray-accelerating shocks, are well confined within the cores of superbubbles. These cores can thus provide a source of cosmic-ray matter of essentially constant metallicity throughout the age of the Galaxy, which is required to account for the constancy of cosmicray-produced Be relative to supernova-produced Fe observed in halo stars formed in the early Galaxy. The interactions of the grains and gas in metal-rich superbubbles, with recurrent supernova shocks every ∼ 5 3 # 10 yr, also reconcile the requirement of a supernova ejecta source of cosmic rays with the recent observations that require a greater than 10 5 yr delay between nucleosynthesis and acceleration for the cosmic-ray metals. Supernovaenriched bubble metallicity may also explain the X-ray emission from the interiors of superbubbles in the Large Magellanic Cloud.

OB Associations, Wolf–Rayet Stars, and the Origin of Galactic Cosmic Rays

“…shown that the 59 Ni, which decays only by electron-capture, has completely decayed, within the measurement uncertainties, to 59 Co (Wiedenbeck et al 1999 The average time between SN events within superbubbles is ~3 × 10 5 years, depending upon the number of massive stars in the OB association (Higdon, et al 1998). In Binns et al (2005) we stated that this gives sufficient time between events for the 59 Ni, which is synthesized in the SN explosions, to decay before its daughter product, 59 Co, is accelerated to cosmic ray energies.…”

Nonthermal particles and photons in starburst regions and superbubbles

“…spectra of MHD fluctuations in a tenuous plasma with frozen-in magnetic fields. The collective effect of multiple SNRs and strong winds of young massive stars in a superbubble may be able to re-energize CR particles (see Montmerle 1979, Cesarsky and Montmerle 1983, Bykov and Fleishman 1992, Axford 1994, Higdon et al 1998, Klepach et al 2000, Bykov and Toptygin 2001, Bykov 2001, Ramaty et al 2001, Parizot et al 2004, Marcowith et al 2005, Ferrand and Marcowith 2010 and even to extend the spectrum of accelerated particles to energies well beyond the Knee (Bykov and Toptygin 2001).…”

On the optical and X-ray afterglows of gamma ray bursts

“…An analysis of historical SNe in the Galaxy (e.g. Higdon & Lingenfelter 1980), of SNe in the LMC (e.g., Dune et al 2001) and of SNe in late-type galaxies (Kennicut et al 1989;van Dyke et al 1996;Higdon et al 1998) indicates that 85 ± 10% of SNe occur in superbubbles (e.g., Lingenfelter et al 2001). These are spaces of typical size 0.1 to 0.5 kpc, surrounding star-formation regions, that extend all the way into the galactic halo, and from which the ISM has been swept away by massive-star winds and previous SNe, resulting in an ISM with a low density (n ∼ 10 −2 to 10 −3 cm −3 ) comparable to that in a galactic halo.…”